Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Use of Recycling-Reflection Color-Purity Enhancement Film to Improve Color Purity of Full-Color Micro-LEDs

Use of Recycling-Reflection Color-Purity Enhancement Film to Improve Color Purity of Full-Color... A common full‑ color method involves combining micro‑light ‑ emitting diodes (LEDs) chips with color conversion materials such as quantum dots (QDs) to achieve full color. However, during color conversion between micro‑LEDs and QDs, QDs cannot completely absorb incident wavelengths cause the emission wavelengths that including incident wavelengths and converted wavelength through QDs, which compromises color purity. The present paper proposes the use of a recycling‑reflection color ‑purity‑ enhancement film (RCPEF) to reflect the incident wavelength multiple times and, consequently, prevent wavelength mixing after QDs conversion. This RCPEF only allows the light of a specific wavelength to pass through it, exciting blue light is reflected back to the red and green QDs layer. The prototype experiment indicated that with an excitation light source wavelength of 445.5 nm, the use of green QDs and RCPEFs increased color purity from 77.2% to 97.49% and light conversion efficiency by 1.97 times and the use of red QDs and RCPEFs increased color purity to 94.68% and light conversion efficiency by 1.46 times. Thus, high effi‑ ciency and color purity were achieved for micro‑LEDs displays. Keywords: Micro‑LEDs, Quantum dots, Color purity, Recycling‑reflection color ‑purity‑ enhancement film, Light conversion efficiency Introduction are required [4, 5]. CCFL backlight elements contain Displays change human reading habits and reduce the "mercury (Hg)" toxic substances, the LEDs (light emitting use of a lot of paper. All people and every industry need diodes) have just solved the shortcomings of CCFL back- a monitor. Billboards, TV screens, mobile phones, house- light elements and have become the current mainstream hold appliances, and car dashboards all use display liquid crystal backlight [6, 7]. Light-emitting diodes applications. Thus, display technical specifications are (LEDs) backlights utilize three types of light sources, with continually improved through research [1, 2]. The earli - white LEDs (WLEDs) currently used in most displays. est display screens used cathode ray tubes (CRTs), with To achieve thinness and lightness, edge-lit backlights are large size and high power consumption being major often used. When the light guide plate is of poor quality, drawbacks [3]. Liquid–crystal displays (LCDs), which hot spots tend to appear, causing problems relating to low largely replaced CRTs, are thin and light. However, LCD light uniformity and light extraction efficiency [8 , 9]. The screens cannot emit light, and thus, the use of backlight second type of light source is a direct-lit backlight, which and the emission of full-color pixels through color filters uses WLEDs and provides more advantages in terms of contrast, brightness, and cost-effectiveness relative to edge-lit backlights [10]. The third light source uses red, green, and blue (RGB) LEDs, but the varying attenuation *Correspondence: imezty@ccu.edu.tw Department of Mechanical Engineering, Advanced Institute rates of this light source cause color shift, increase pro- of Manufacturing with High‑Tech Innovations, National Chung Cheng duction cost, and impose a high technical threshold [11, University, 168, University Rd., Min‑Hsiung, Chia‑Yi 62102, Taiwan © The Author(s) 2021. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Ye and Wu Nanoscale Research Letters (2022) 17:1 Page 2 of 10 12]. The LCD is still the current mainstream display, but LEDs is a complicated and time-consuming task [30, 31]. its lack of self-luminosity leads to poor overall control Moreover, compared with blue and green LED chips, red efficiency with respect to the interaction of the backlight LED chips are prone to generating excessive heat due to with the liquid crystal through the color filter and two their material absorption properties, resulting in poor polarizers. This drawback has attracted much criticism photoelectric conversion efficiency and low EQE. Con - [13]. In contrast to LCDs, organic LEDs (OLEDs) display sequently, they cannot meet display requirements [32]. technology does not require a backlight and instead uses Chen et  al. applied directional control over RGB micro- a thin coating of organic light-emitting materials. The LEDs made on a 4-in patterned sapphire substrate to material of the light-emitting layer allows for the three achieve a wide color gamut of 114.4% (National Television primary colors of red, green, and blue to be produced System Committee, NTSC) and 85.4% (Rec. 2020) [33]. [14, 15]. Multiple studies have examined OLEDs display Qi et al. built a micro-LEDs array on a 0.55-in (400 × 240) technology. Ai et al. proposed an OLEDs display technol- gallium nitride substrate with a pixel density of 848 PPI ogy based on a combination of perovskite and LEDs, and and full width at half maximum (FWHM) of 18.2  nm to at an excitation wavelength of 710 nm, its external quan- produce a high-brightness, high-resolution micro-LEDs tum efficiency (EQE) reached 27% [16]. Chen et  al. pro - display [34]. The aforementioned findings indicate that posed a high-efficiency red OLEDs display with an EQE of combining blue micro-LEDs with QDs is currently the 25.2% at a peak excitation wavelength of 680 nm [17]. Hu best solution for achieving full color. Micro-LEDs have proposed a full-color blue organic LEDs with a patterned the advantages of high contrast, low power consumption, red–green quantum dots (QDs) color conversion layer long life, and fast response time, but they can be improved and achieved a color gamut standard (BT.2020) of 95% further [35]. Zhang et  al. proposed the use of pure blue with a 6.6-in full-color display [18]. In contrast to LCDs, double-shell InP/(ZnS) QDs with an emission wavelength OLEDs can emit light and do not require a backlight mod- of 468 nm and a quantum yield of 45%, and they managed ule. However, due to the characteristics of organic materi- to increase EQE by 2.8 times [36]. Yang Li et al. proposed als, a static image is prone to burn-in after a long period the application of microfluidic technology combined of use. This is the current problem that affects OLEDs with a red–green perovskite QDs color conversion layer [19, 20]. QLEDs (quantum dots light-emitting diodes) for use in micro-LEDs displays and achieved a wide color utilize QDs display technology. QDs are characterized by gamut (NTSC) of 131% [37]. Yin et al. combined CsPbBr3 wide absorption and narrow emission [21, 22]. Backlight perovskite and CdSe QDs to develop a green–red color blue LEDs produce excellent red, green, and blue light conversion layer that achieved a color gamut standard through QDs films, which provide excellent color satura - (NTSC) of 129% [38]. Shih et  al. suggested the use of tion performance. However, this technology is classified QDs composite materials in place of color filters for full- as a non-self-luminous light source technology [23, 24]. color displays and achieved 86.16% conversion efficiency Su et  al. explored the use of red, green, and blue trans- through the implementation of a QDs color conversion parent QLEDs that are built on a flexible plastic substrate layer [39]. Furthermore, current displays add a color filter and vertically integrated with UV glue. They reported to improve color purity, which absorbs most of the wave- EQE levels of 12.0%, 8.5%, and 4.5% for red, green, and length band and only allows specific wavelengths to pass. blue transparent QLEDs, respectively, demonstrating the u Th s, light extraction efficiency is substantially compro - feasibility of individually controllable RGB QLEDs [25]. mised [40–42]. Few studies have focused on improving Another predecessor of micro-LEDs technology is mini the color purity of micro-LEDs hybrid QDs. Poor color LEDs technology. The advantage of mini LEDs is their purity results in poor color saturation and reduces the small size. Ye et al. proposed a modified package structure range of the color gamut that can be displayed by a moni- for optimizing the light field type of mini LEDs, which tor. Therefore, the enhancement of color purity is crucial. can be used as a backlight source for display and lighting The present paper proposes the use of an RCPEF that [26, 27]. The Scholars have recently conducted extensive combines red and green QDs and blue micro-LEDs. This research on extremely small RGB micro-LEDs, which RCPEF only allows the light of a specific wavelength to all use inorganic semiconductor materials. The mate - pass through it, excited blue light is reflected back to the rial properties of such LEDs grant them the advantages red and green QDs layer, and the corresponding red and of photoelectric conversion efficiency, high brightness, green lights are emitted after being absorbed by the QDs, high reliability, and fast response times [28, 29]. However, thereby improving color purity and reducing absorption their application in large panel screens leads to difficul - (which leads to substantial light loss). This proposed solu - ties in performing the mass transfer and technical prob- tion meets display requirements by enabling high conver- lems relating to maintenance. When black spots or color sion efficiency and high color saturation. shifts appear on the screen, the replacement of sporadic Y e and Wu Nanoscale Research Letters (2022) 17:1 Page 3 of 10 Definition of Light Conversion Efficiency Methods Conversion efficiency refers to the ratio of effective out - Definition of Color Purity put energy to input energy. Light conversion efficiency Color purity indicates how close the color of a sample is can be obtained using Eq. (2): to its dominant wavelength spectrum and is defined as the ratio of the distance between the chromaticity coor- Area (g, r) or (G, R) dinates of the measured object and CIE1931 center ver- Light conversion efficiency := × 100% Area + Area g, r or (G, R) ( ) sus the distance between the chromaticity coordinates (2) of the standard light source and CIE1931 center. Color where Area is the total radiated power in the red and purity can be calculated using Eq.  (1). (x , y ) are the (g, r) d d green bands without RCPEF, Ar ea is the total radi- coordinates for the main wavelength spectrum’s color (G, R) ated power in the red and green bands with a layer of light source, (x , y ) are the chromaticity coordinates s s RCPEF, and Area is the total radiated power in the blue of the measured object, and (x , y ) are the chromaticity i i band (all units are in mW). coordinates for the CIE1931 center. Preparation Process for Red and Green Quantum Dots (x − x ) + y − y s i s i Color purity =  × 100 The quantum dots used in this study are red and green (1) (x − x ) + y − y CdSe/ZnS, the main reaction materials are cadmium d i d i oxide (CdO), zinc oxide (ZnO), silicon (Se), trioctyl phosphine oxide (TOP), lauric acid (LA, C H O ), 12 24 2 and n-hexane (C H ). Hexadecylamine (HDA) is used 6 14 to prevent the agglomeration reaction of QDs, metha- nol (CH OH) is used to prevent the agglomeration reaction, and argon (Ar) is used throughout the pro- cess to ensure environmental vacuum. The first part of the production process involves mixing 0.0049  g CdO, 0.0308 g ZnO, and 1.7495 g LA in a three-necked flask, then pour argon and stir the mixture with a magnet and heat it to 230  °C. After reaching 230  °C, the mix- ture was naturally cooled to 30  °C. The cooling time is used to prepare the precursor. The preparation involves injecting 0.0948 g of Se into TOP and n-hexane to form a mixture, and then shaking to completely dissolve the Fig. 1 Samples of a red and b green QDs red CdSe/ZnS emission 0.9 green CdSe/ZnS emission 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 450475 500525 550575 600625 650675 700725 750 Wavelength(nm) Fig. 2 Schematic diagram of the normalized spectral radiance of red and green CdSe/ZnS Normalized intensity (a.u.) Ye and Wu Nanoscale Research Letters (2022) 17:1 Page 4 of 10 Table 1 Specifications of red and green CdSe/ZnS samples The normalization spectral of the red and green CdSe/ZnS quantum dots are shown in Fig. 2. The emis - Red CdSe/ZnS Green CdSe/ZnS sion wavelength and FWHM of the red CdSe/ZnS Wavelength (nm) 633.5 nm 531.5 nm quantum dots are 633.5 and 41.5  nm. The emission FWHM (nm) 41.5 nm 22 nm wavelength and FWHM of the green CdSe/ZnS quan- Concentration weight (wt%) 20 wt% 20 wt% tum dots are 531.5 and 22 nm. Particle diameters (nm) 4.4 nm 3.3 nm The specifications of the red and green CdSe/ZnS QDs samples are shown in Table  1. The measurement results of the photoluminescence (PL) spectrometer show that the emission wavelength and FWHM of the Se in TOP and n-hexane. Cool the main reactant to red CdSe/ZnS QDs are 633.5 and 41.5  nm, and the 30  °C, add 3.2505  g HDA, heat the mixture to 230  °C, emission wavelength and FWHM of the green CdSe/ and heat the red QDs to 300  °C, and the green QDs to ZnS QDs are 531.5 and 22  nm. The concentration of 320  °C. Then the prepared precursor is added and the the red and green CdSe/ZnS QDs samples is 20 wt%. By reaction time is controlled. The reaction time between controlling the reaction time of the main reactant CdO the red light quantum dots and the precursor is 60  s, and the precursor Se, the particle size of the red CdSe/ and the reaction time between the green light quantum ZnS QDs is 4.4  nm and the particle size of the green dots and the precursor is 3  s. After the reaction was CdSe/ZnS QDs is 3.3 nm. completed, the mixture was quickly cooled to 150  °C, and methanol heated to about 60  °C was added to ter- RCPEF Principle and Optimal Design minate the agglomeration reaction. Finally, centrifuge We propose the use of RCPEF to achieve high color at 5000 rpm for 10 min, pour out the methanol, and air purity. When the excited blue light wavelength emitted dry. Samples of red and green QDs are shown in Fig. 1. by an LEDs passes through red and green QDs, the ina- Figure 1a shows a red light CdSe/ZnS QDs sample, and bility of the QDs to completely absorb the incident wave- Fig. 1b shows a green light CdSe/ZnS QDs sample. Both length means that the total emission wavelength is the red and green QDs are mixed in n-hexane solution. Fig. 3 RCPEF color purity improvement principle: a no RCPEF light emission, b traditional color filter architecture, and c combined RCPEF light emission architecture Y e and Wu Nanoscale Research Letters (2022) 17:1 Page 5 of 10 In the present study, Essential Macleod (Thin Film Center Inc.) simulation software was used to design the recovery of reflected color purity to enhance the film. The optimal design was achieved using the formula Air/ (HL) /SUB of the membrane stack, where L is the low refractive index material SiO , H is the high refractive index material T iO , M is the constant (i.e., the power of the membrane stack), and SUB is the substrate mate- rial (i.e., glass). The optimization calculations indicated that when M = 12, the 500 nm waveband size ripple was large and the difference between an M of 13 and 14 was Fig. 4 RCPEF bandpass film simulation small. Therefore, better results can be obtained when M = 13. The overall physical thickness was 1442.02 nm. After optimization (Fig.  4), the wavelength band was emission wavelength of the incident wavelength of the less than 470  nm for the high reflection area with a mixed QDs (Fig. 3a), which leads to poor color purity and penetration rate less than 1%, and the wavelength band color cast problems. The traditional solution is to add a was greater than 510  nm for the high penetration area color filter (CF) layer and apply the principle of material with a penetration rate greater than 92%. absorption to absorb the blue light, such that the corre- sponding green and red pixels only emit green and red light, respectively. Although a higher color purity can be Structure of High‑Color‑Purity Full‑Color Micro‑LEDs obtained, a considerable amount of energy is lost due to The processing steps and structure of high-color- material absorption as presented in Fig.  3b. To address purity full-color micro-LEDs are shown in Fig.  5. Fig- this problem in the present study, a layer of RCPEF was ure  5a shows a flexible FR4 flexible substrate. (FR-4 added above the red-green QDs of the color conver- is a composite material made from a woven fiberglass sion layer. As shown in Fig. 3c, when part of the incident cloth and epoxy resin binder.) First, blue micro-LEDs wavelength (blue light) passed through the RCPEF, the were die-bonded onto the FR4 substrate (Fig.  5b). A RCPEF reflected the blue band back to the QDs color layer of CdSe red and green QDs was then applied on conversion layer, and the red and green QDs absorbed specific pixels through dispensation (Fig.  5c, d), and again to re-excite and re-emit red and green wavelengths. a layer of RCPEF was then added above the red and After several cycles, relatively pure RGB colors were green QDs pixels (Fig. 5e). obtained. Fig. 5 Structure of high‑ color‑purity full‑ color micro‑LEDs: a flexible FR4 substrate, b die ‑bonding of blue micro ‑LEDs on FR‑4, c dispensation of red‑light QDs layer, d dispensation of green‑light QDs layer, e and completion of high‑ color‑purity full‑ color micro‑LEDs with RCPEF Ye and Wu Nanoscale Research Letters (2022) 17:1 Page 6 of 10 Fig. 6 Images of micro‑LEDs obtained using a scanning electron microscope. a top and b bottom views The normalized spectrum of the light source of the blue micro-LEDs chip is shown in Fig. 7. The wavelength peak and FWHM were 445.5 and 16 nm, and the color purity was 98.23%. Measurement Data of RCPEF Figure 8 shows the RCPEF sample and presents its meas- urement data. Figure  8a shows the sample, which meas- ures 5  cm × 5  cm. Figure  8b presents the comparison of the simulated and measured data of the RCPEF, indicat- Fig. 7 Normalized spectrum of blue micro‑LEDs chip ing a high consistency between the simulated and meas- ured transmittance rates. RCPEF for Green QDs Results and Discussion The blue micro-LEDs were converted from green QDs Blue Micro‑LEDs Chip to green light. The normalized spectrum is shown in The blue LEDs chip had a flip-chip structure, and its Fig.  9. The peak emission of green light was 531.5  nm, length, width, and height were 140, 240, and 100  μm, and the FWHM was 22 nm. Most of the light emitted at respectively. Figure  6 shows the images of the micro- this point was radiant blue light. The green light conver - LEDs that were obtained using a scanning electron sion efficiency was only 27.08%, and the color purity was microscope. 77.2%. Notably, the color purity at this point was greatly Fig. 8 RCPEF sample: a prototype sample, b measured value of penetration rate of RCPEF Y e and Wu Nanoscale Research Letters (2022) 17:1 Page 7 of 10 300350 400450 500550 600650 700750 800 300350 400450 500550 600650 700750 800 Fig. 9 Normalized blue light without RCPEF conversion to green Fig. 12 Normalized blue light without RCPEF conversion to red spectrum by QDs spectrum by QDs 100 100 80 80 60 60 40 40 300350 400450 500550 600650 700750 800 Fig. 10 Conversion of normalized blue light to a green spectrum by Fig. 13 Conversion of normalized blue light to red light by QDs after QDs after addition of RCPEF addition of RCPEF than the light conversion efficiency that was observed when the RCPEF was not used. At this point, the color purity could be increased to 97.49%. The data for the blue-to-green light conversion are shown in Fig. 11. Figure 11a shows the color of the emit- ted light without RCPEF. Because most of the emitted light was in the incident blue wavelength band, the color of the emitted light was the color mixed by the green quantum mixing incident wavelength, which led to a color shift that was similar to cyan. The addition of the RCPEF changed the color of the emitted light (Fig.  11b). Fig. 11 Green QDs sample a before and b after addition of RCPEF The part of the incident wavelength that the QDs could not absorb was reflected by the RCPEF back to the QDs layer for reabsorption and re-excitation, and it was then affected by blue light, such that the color conversion effi - radiated as green light to obtain purer green light. At this ciency, color purity, and light conversion efficiency were point, the color purity could be increased to 97.49%. not ideal and a clear color shift was observed. After the addition of the RCPEF, a normalized blue-to- RCPEF for Red QDs green spectrum was achieved (Fig.  10). The light green Blue micro-LEDs were converted into red light through emission peak was 532 nm, and the FWHM was 21 nm. red QDs. The data for the conversion of normalized blue Some incident wavelengths that could not be absorbed by light to the red light spectrum are shown in Fig.  12. The the QDs were radiated again after being reflected to the peak of red light was 633.5  nm, and the FWHM was QDs layer by the RCPEF. The light conversion efficiency 41.5 nm. Most of the emitted light was incident light blue, of green light was 53.43%, which was 1.97 times higher Ye and Wu Nanoscale Research Letters (2022) 17:1 Page 8 of 10 After the addition of the RCPEF, a normalized blue- to-red spectrum was achieved (Fig. 13). The peak emis - sion of red light was 634  nm, and the FWHM was 40.5  nm. Some incident wavelengths that could not be absorbed by the QDs were reflected by the RCPEF to the QDs layer for reabsorption, re-excitation, and re- emission as red light. The light conversion efficiency of red light was increased to 31.77%, which was 1.46 times higher than light conversion efficiency that was observed before the addition of the RCPEF, and the Fig. 14 Red QDs sample a before and b after addition of RCPEF color purity was increased to 94.68%. Figure  14 presents a practical example of the con- version of blue light to red light. Figure  14a shows the color of the emitted light before the addition of the RCPEF. Because most of the emitted light was in the incident blue light band, the light conversion efficiency for red light was only 21.78%. Therefore, the color of the obtained emitted light was red converted by mix- ing the QDs with the incident wavelength, and its color shift was similar to a magenta color. After the addition of the RCPEF, the color of the emitted light shown in Fig.  14b was achieved. Some incident wavelengths that could not be absorbed by the QDs were reflected by the RCPEF to the QDs layer to be reabsorbed and radiated as red light after excitation. A purer red light could be obtained. The color purity was increased to 94.68%. Figure  15 shows the color purity of the micro-LEDs sample. The light emitted by the sample after the addi - tion of the RCPED is shown in Fig.  15b—compared with the image in Fig. 15a, the light color of the sample exhibits purer RGB colors. Red, green, and blue color purity were 94.68%, 97.49%, and 98.23%. Fig. 15 Micro‑LEDs colors a before and b after addition of RCPEF Table  2 presents the comparison of the color purity and light conversion efficiency of blue micro-LEDs with differing configurations (i.e., with or without RCPEF and at this point, the light conversion efficiency was only and with or without red or green QDs). After the addi- 21.78%. Moreover, the color purity value was not indica- tion of the RCPEF, the color purity of red and green QDs tive because most of the wavelength band that contrib- was increased to 94.68% and 97.49%. The light conver - uted to this value was the light emitted by the incident sion efficiency of red and green QDs was increased by light-blue light and not that of the red light. Therefore, 1.46 and 1.97 times. The experimental results indicated the resulting color purity and light conversion efficiency that the combination of the blue micro-LEDs with red were not ideal, and a clear color shift phenomenon was and green QDs and the RCPEF effectively improved color observed. purity and light conversion efficiency. Table 2 Comparison of blue micro‑LEDs with differing configurations Type Only blue micro‑LEDs Blue micro‑LEDs with G‑ QDs Blue micro‑LEDs with R‑ QDs RCPEF Without filter Without RCPEF With RCPEF Without RCPEF With RCPEF Light conversion efficiency (%) 100% 27.08% 53.43% 21.78% 31.77% Peak wavelength (nm) 445.5 nm 531.5 nm 532 nm 633.5 nm 634 nm FWHM (nm) 16 nm 22 nm 21 nm 41.5 nm 40.5 nm Y e and Wu Nanoscale Research Letters (2022) 17:1 Page 9 of 10 Received: 15 August 2021 Accepted: 16 December 2021 Conclusions This research suggests that combining blue micro- LEDs with red and green QDs and a layer of RCPEF can improve color purity and light conversion efficiency. The References incident blue-light wavelengths that cannot be com- 1. Chen HW, Lee JH, Lin BY, Chen S, Wu ST (2018) Liquid crystal display and pletely absorbed by the QDs are reflected to the color organic light‑ emitting diode display: present status and future perspec‑ tives. Light Sci Appl 7:17168. https:// doi. org/ 10. 1038/ lsa. 2017. 168 conversion layer. Subsequently, they are reabsorbed 2. Huang Y, Hsiang EL, Deng MY, Wu ST (2020) Mini‑LED, Micro ‑LED and by red and green QDs for re-excitation and radiation, OLED displays: present status and future perspectives. Light Sci Appl thereby achieving high color purity and high conversion 9:105. https:// doi. org/ 10. 1038/ s41377‑ 020‑ 0341‑9 3. Qi Y, Xiao X, Lu Y, Shu J, Wang J, Chen M (2019) Cathode ray tubes glass efficiency. Thus, the problem of poor color purity in color recycling: a review. Sci Total Environ 650(Pt 2):2842–2849. https:// doi. org/ conversions between micro-LEDs and QDs is alleviated. 10. 1016/j. scito tenv. 2018. 09. 383 Furthermore, because RCPEF is a type of feedback 4. Desroches L‑B, Ganeshalingam M (2015) The dynamics of incremental costs of efficient television display technologies. Technol Forecast Soc reflection, conversion efficiency can be improved. The Change 90:562–574. https:// doi. org/ 10. 1016/j. techf ore. 2014. 02. 016 prototype experimental data indicate that with the addi- 5. Lin C‑H (2006) Digital‑ dimming controller with current spikes elimination tion of an RCPEF layer, the color purity of the red and technique for LCD backlight electronic ballast. IEEE Trans Ind Electron 53(6):1881–1888. https:// doi. org/ 10. 1109/ tie. 2006. 885143 green quantum dots increased to 94.68% and 97.49%, 6. Hong T‑ Y, Chien C‑F (2020) A simulation‑based dynamic scheduling and respectively, and the light conversion efficiency of the red dispatching system with multi‑ criteria performance evaluation for Indus‑ and green quantum dots increased by 1.46 times and 1.97 try 3.5 and an empirical study for sustainable TFT‑LCD array manufactur ‑ ing. Int J Prod Res 58(24):7531–7547. https:// doi. org/ 10. 1080/ 00207 543. times, respectively. The addition of the RCPEF effectively 2020. 17773 42 improves the color purity and light conversion efficiency 7. Wu C, Wang X, Lin L, Guo H, Wang ZL (2016) Paper‑based triboelectric of light such that micro-LEDs displays can achieve higher nanogenerators made of stretchable interlocking Kirigami patterns. ACS Nano 10(4):4652–4659. https:// doi. org/ 10. 1021/ acsna no. 6b009 49 color saturation and light output efficiency, thus enhanc - 8. Yuan F, He P, Xi Z, Li X, Li Y, Zhong H, Fan L, Yang S (2019) Highly efficient ing their display specifications and commercial value. In and stable white LEDs based on pure red narrow bandwidth emission the future, the application of micro-patterning in ultra- triangular carbon quantum dots for wide‑ color gamut backlight displays. Nano Res 12(7):1669–1674. https:// doi. org/ 10. 1007/ s12274‑ 019‑ 2420‑x high-pixel micro-LEDs displays can be further examined. 9. Chen H, Zhu R, Tan G, Li MC, Lee SL, Wu ST (2017) Enlarging the color gamut of liquid crystal displays with a functional reflective polarizer. Opt Express 25(1):102–111. https:// doi. org/ 10. 1364/ OE. 25. 000102 Abbreviations 10. Lee TX, Chen BS (2016) High uniformity and tolerance design for direct‑lit B: Blue; CF: Color filter; CRT : Cathode ray tube; EQE: External quantum effi‑ LED backlight illumination using lagrange interpolation (in English). J ciency; FWHM: Full width at half maximum; G: Green; HDA: HEXADECYL amine; Disp Technol 12(11):1403–1410. https:// doi. org/ 10. 1109/ jdt. 2016. 26066 49 LA: Lauric acid; LCD: Liquid–crystal display; LEDs: Light‑ emitting diodes; NTSC: 11. Oh JH, Kang H, Ko M, Do YR (2015) Analysis of wide color gamut of green/ National television system committee; OLEDs: Organic light‑ emitting diode; red bilayered freestanding phosphor film‑ capped white LEDs for LCD QDs: Quantum dots; QDF: Quantum dots film; QLEDs: Quantum dots light ‑ backlight. Opt Express 23(15):A791‑804. https:// doi. org/ 10. 1364/ OE. 23. emitting diodes; R: Red; RCPEF: Reflection color purity enhancement film; SEM: 00A791 Scanning electron microscope; TOP: Trioctylphosphine; W: White. 12. Chen H‑ W, Zhu R‑D, He J, Duan W, Wei Hu, Yan‑ Qing Lu, Li M‑ C, Lee S‑L, Dong Y‑ J, Shin‑ Tson Wu (2017) Going beyond the limit of an LCD’s color Acknowledgements gamut. Light Sci Appl 6(9):e17043. https:// doi. org/ 10. 1038/ lsa. 2017. 43 This research was supported by the Ministry of Science and Technology, 13. Chen H, Zhu R, Li MC, Lee SL, Wu ST (2017) Pixel‑by‑pixel local dimming the Republic of China (Grant No. MOST 110‑2221‑E‑194‑036 and MOST for high‑ dynamic‑range liquid crystal displays. Opt Express 25(3):1973– 110‑2622‑E‑194‑007). 1984. https:// doi. org/ 10. 1364/ OE. 25. 001973 14. Song J, Lee H, Jeong EG, Choi KC, Yoo S (2020) Organic light‑ Authors’ Contributions emitting diodes: pushing toward the limits and beyond. Adv Mater ZTY designed the experiments. J‑ YW analyzed data. ZTY and J‑ YW discussed 32(35):e1907539. https:// doi. org/ 10. 1002/ adma. 20190 7539 the results and contributed to the writing of the manuscript. Both authors 15. Wang S, Zhang H, Zhang B, Xie Z, Wong W‑ Y (2020) Towards high‑power ‑ read and approved the final manuscript. efficiency solution‑processed OLEDs: material and device perspectives. Mater Sci Eng R Rep. https:// doi. org/ 10. 1016/j. mser. 2020. 100547 Funding 16. Ai X, Evans EW, Dong S, Gillett AJ, Guo H, Chen Y, Hele TJ, Friend RH, This work was financially/partially supported by the Advanced Institute of Li F (2018) Efficient radical‑based light ‑ emitting diodes with dou‑ Manufacturing with High‑ Tech Innovations from the Featured Areas Research blet emission. Nature 563(7732):536–540. https:// doi. org/ 10. 1038/ Center Program within the framework of the Higher Education Sprout Project s41586‑ 018‑ 0695‑9 by the Ministry of Education in Taiwan. 17. Chen JX, Tao WW, Chen WC, Xiao YF, Wang K, Cao C, Yu J, Li S, Geng FX, Adachi C, Lee CS (2019) Red/near‑infrared thermally activated delayed Available of Data and Materials fluorescence OLEDs with near 100% internal quantum efficiency. Angew The datasets supporting the conclusions of this article are available in the Chemie 131(41):14802–14807. https:// doi. org/ 10. 1002/ anie. 20190 6575 article. 18. Hu Z, Yin Y, Ali MU, Peng W, Zhang S, Li D, Zou T, Li Y, Jiao S, Chen SJ, Lee CY (2020) Inkjet printed uniform quantum dots as color conversion layers Declaration for full‑ color OLED displays. Nanoscale 12(3):2103–2110. https:// doi. org/ 10. 1039/ c9nr0 9086j Competing interests 19. Xu Z, Gu J, Qiao X, Qin A, Tang BZ, Ma D (2019) Highly efficient deep blue The authors declare that they have no competing interests. aggregation‑induced emission organic molecule: a promising multifunc‑ tional electroluminescence material for blue/green/orange/red/white Ye and Wu Nanoscale Research Letters (2022) 17:1 Page 10 of 10 OLEDs with superior efficiency and low roll‑ off. ACS Photon 6(3):767–778. 38. Yin Y, Hu Z, Ali MU, Duan M, Gao L, Liu M, Peng W, Geng J, Pan S, Wu https:// doi. org/ 10. 1021/ acsph otoni cs. 8b017 24 Y, Hou J (2020) Full‑ color micro‑LED display with CsPbBr 3 perovskite 20. Pang Z, Sun D, Zhang C, Baniya S, Kwon O, Vardeny ZV (2017) Manipula‑ and CdSe quantum dots as color conversion layers. Adv Mater Technol tion of emission colors based on intrinsic and extrinsic magneto‑ electro‑ 5(8):2000251. https:// doi. org/ 10. 1002/ admt. 20200 0251 luminescence from exciplex organic light‑ emitting diodes. ACS Photon 39. Shih YC, Shi FG (2017) Quantum dot based enhancement or elimina‑ 4(8):1899–1905. https:// doi. org/ 10. 1021/ acsph otoni cs. 7b005 67 tion of color filters for liquid crystal display. IEEE J Sel Top Quant Electron 21. Chen LC, Tien C‑H, Chen DF, Kuo HC, Ye ZT (2019) High‑uniformity 23(5):1–4. https:// doi. org/ 10. 1109/ jstqe. 2017. 27489 23 planar mini‑ chip‑scale packaged LEDs with quantum dots converter 40. Ma Y, Xin SJ, Liu X, Liu Y, Sun J, Wang X, Guo Q, Chigrinov VG (2020) for white light source. Nanoscale Res Lett. https:// doi. org/ 10. 1186/ Colour generation for optically driving liquid crystal display. Liq Crystals s11671‑ 019‑ 2993‑z 47(12):1729–1734. https:// doi. org/ 10. 1080/ 02678 292. 2020. 17215 80 22. Won Y‑H, Cho O, Kim T, Chung D ‑ Y, Kim T, Chung H, Jang H, Lee J, Kim D, 41. Itoh Y, Langlotz T, Iwai D, Kiyokawa K, Amano T (2019) Light attenuation Jang E (2019) Highly efficient and stable InP/ZnS/ZnS quantum dot light ‑ display: subtractive see‑through near ‑ eye display via spatial color filter ‑ emitting diodes. Nature 575(7784):634–638. https:// doi. org/ 10. 1038/ ing. IEEE Trans Vis Comput Graph 25(5):1951–1960. https:// doi. org/ 10. s41586‑ 019‑ 1771‑51109/ TVCG. 2019. 28992 29 23. Lan X, Chen M, Hudson MH, Kamysbayev V, Wang Y, Guyot‑Sionnest 42. Ji C, Lee KT, Xu T, Zhou J, Park HJ, Guo LJ (2017) Engineering light at the P, Talapin DV (2020) Quantum dot solids showing state‑resolved nanoscale: structural color filters and broadband perfect absorbers. Adv band‑like transport. Nat Mater 19(3):323–329. https:// doi. org/ 10. 1038/ Opt Mater. https:// doi. org/ 10. 1002/ adom. 20170 0368 s41563‑ 019‑ 0582‑2 24. Keum H, Jiang Y, Park JK, Flanagan JC, Shim M, Kim S (2018) Photoresist Publisher’s Note contact patterning of quantum dot films. ACS Nano 12(10):10024–10031. Springer Nature remains neutral with regard to jurisdictional claims in pub‑ https:// doi. org/ 10. 1021/ acsna no. 8b044 62 lished maps and institutional affiliations. 25. Su Q, Zhang H, Chen S (2021) Flexible and tandem quantum‑ dot light‑ emitting diodes with individually addressable red/green/blue emission. npj Flexible Electron. https:// doi. org/ 10. 1038/ s41528‑ 021‑ 00106‑y 26. Ye ZT, Ruan MJ, Kuo HC (2020) CSP‑leds combined with light guide with‑ out reflective matrix for antiglare design. IEEE Access 8:156718–156726. https:// doi. org/ 10. 1109/ access. 2020. 30193 14 27. Ye ZT, Chang C, Juan MC, Chen KJ (2020) luminous intensity field optimi‑ zation for antiglare LED desk lamp without second optical element. Appl Sci Basel 10(7):13. https:// doi. org/ 10. 3390/ app10 072607 28. Lee HE et al (2019) Wireless powered wearable micro light‑ emitting diodes. Nano Energy 55:454–462. https:// doi. org/ 10. 1016/j. nanoen. 2018. 11. 017 29. Kim K, Voroslakos M, Seymour JP, Wise KD, Buzsaki G, Yoon E (2020) Artifact‑free and high‑temporal‑resolution in vivo opto ‑ electrophysiology with microLED optoelectrodes. Nat Commun 11(1):2063. https:// doi. org/ 10. 1038/ s41467‑ 020‑ 15769‑w 30. Xuan T, Shi S, Wang L, Kuo HC, Xie RJ (2020) Inkjet‑printed quantum dot color conversion films for high‑resolution and full‑ color micro light‑ emitting diode displays. J Phys Chem Lett 11(13):5184–5191. https:// doi. org/ 10. 1021/ acs. jpcle tt. 0c014 51 31. Pan Z, Guo C, Wang X, Liu J, Cao R, Gong Y, Wang J, Liu N, Chen Z, Wang L, Ishikawa M (2020) Wafer‑scale micro ‑LEDs transferred onto an adhesive film for planar and flexible displays. Adv Mater Technol 5(12):200549. https:// doi. org/ 10. 1002/ admt. 20200 0549 32. Yuan Z, Shujie G, Xia Mao Gu, Simin ZY, Xianbo Wu, Jing W, Nan Z, Zhi Z (2019) Enhancing quantum efficiency and tuning photoluminescence properties in far‑red‑ emitting phosphor Ca14Ga10Zn6O35:Mn4+ based on chemical unit engineering. Chem Eng J 374:381–391. https:// doi. org/ 10. 1016/j. cej. 2019. 05. 201 33. Chen SW, Huang YM, Singh KJ, Hsu YC, Liou FJ, Song J, Choi J, Lee PT, Lin CC, Chen Z, Han J (2020) Full‑ color micro‑LED display with high color sta‑ bility using semipolar (20–21) InGaN LEDs and quantum‑ dot photoresist. Photon Res 8(5):630–636. https:// doi. org/ 10. 1364/ prj. 388958 34. Qi L, Zhang X, Chong WC, Li P, Lau KM (2021) 848 ppi high‑brightness active‑matrix micro ‑LED micro ‑ display using GaN‑ on‑Si epi‑ wafers towards mass production. Opt Express 29(7):10580–10591. https:// doi. org/ 10. 1364/ OE. 419877 35. Zhou X, Tian P, Sher CW, Wu J, Liu H, Liu R, Kuo HC (2020) Growth, transfer printing and colour conversion techniques towards full‑ colour micro‑LED display. Prog Quant Electron 1(71):100. https:// doi. org/ 10. 1016/j. pquan telec. 2020. 100263 36. Zhang W, Ding S, Zhuang W, Wu D, Liu P, Qu X, Liu H, Yang H, Wu Z, Wang K, Sun XW (2020) InP/ZnS/ZnS core/shell blue quantum dots for efficient light‑ emitting diodes. Adv Funct Mater 30(49):2005303. https:// doi. org/ 10. 1002/ adfm. 20200 5303 37. Li Y, Tao J, Wang Q, Zhao Y, Sun Y, Li P, Lv J, Qin Y, Wang W, Zeng Q, Liang J (2021) Microfluidics‑based quantum dot color conversion layers for full‑ color micro‑LED display. Appl Phys Lett 118(17):173501. https:// doi. org/ 10. 1063/5. 00478 54 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Nanoscale Research Letters Springer Journals

Use of Recycling-Reflection Color-Purity Enhancement Film to Improve Color Purity of Full-Color Micro-LEDs

Ye, Zhi Ting; Wu, Jun-Yi
Nanoscale Research Letters , Volume 17 (1) – Jan 3, 2022
Download PDF
10 pages

Loading next page...
 
/lp/springer-journals/use-of-recycling-reflection-color-purity-enhancement-film-to-improve-mPkQNI40Mp

References (45)

Publisher
Springer Journals
Copyright
Copyright © The Author(s) 2021
ISSN
1931-7573
eISSN
1556-276X
DOI
10.1186/s11671-021-03642-8
Publisher site
See Article on Publisher Site

Abstract

A common full‑ color method involves combining micro‑light ‑ emitting diodes (LEDs) chips with color conversion materials such as quantum dots (QDs) to achieve full color. However, during color conversion between micro‑LEDs and QDs, QDs cannot completely absorb incident wavelengths cause the emission wavelengths that including incident wavelengths and converted wavelength through QDs, which compromises color purity. The present paper proposes the use of a recycling‑reflection color ‑purity‑ enhancement film (RCPEF) to reflect the incident wavelength multiple times and, consequently, prevent wavelength mixing after QDs conversion. This RCPEF only allows the light of a specific wavelength to pass through it, exciting blue light is reflected back to the red and green QDs layer. The prototype experiment indicated that with an excitation light source wavelength of 445.5 nm, the use of green QDs and RCPEFs increased color purity from 77.2% to 97.49% and light conversion efficiency by 1.97 times and the use of red QDs and RCPEFs increased color purity to 94.68% and light conversion efficiency by 1.46 times. Thus, high effi‑ ciency and color purity were achieved for micro‑LEDs displays. Keywords: Micro‑LEDs, Quantum dots, Color purity, Recycling‑reflection color ‑purity‑ enhancement film, Light conversion efficiency Introduction are required [4, 5]. CCFL backlight elements contain Displays change human reading habits and reduce the "mercury (Hg)" toxic substances, the LEDs (light emitting use of a lot of paper. All people and every industry need diodes) have just solved the shortcomings of CCFL back- a monitor. Billboards, TV screens, mobile phones, house- light elements and have become the current mainstream hold appliances, and car dashboards all use display liquid crystal backlight [6, 7]. Light-emitting diodes applications. Thus, display technical specifications are (LEDs) backlights utilize three types of light sources, with continually improved through research [1, 2]. The earli - white LEDs (WLEDs) currently used in most displays. est display screens used cathode ray tubes (CRTs), with To achieve thinness and lightness, edge-lit backlights are large size and high power consumption being major often used. When the light guide plate is of poor quality, drawbacks [3]. Liquid–crystal displays (LCDs), which hot spots tend to appear, causing problems relating to low largely replaced CRTs, are thin and light. However, LCD light uniformity and light extraction efficiency [8 , 9]. The screens cannot emit light, and thus, the use of backlight second type of light source is a direct-lit backlight, which and the emission of full-color pixels through color filters uses WLEDs and provides more advantages in terms of contrast, brightness, and cost-effectiveness relative to edge-lit backlights [10]. The third light source uses red, green, and blue (RGB) LEDs, but the varying attenuation *Correspondence: imezty@ccu.edu.tw Department of Mechanical Engineering, Advanced Institute rates of this light source cause color shift, increase pro- of Manufacturing with High‑Tech Innovations, National Chung Cheng duction cost, and impose a high technical threshold [11, University, 168, University Rd., Min‑Hsiung, Chia‑Yi 62102, Taiwan © The Author(s) 2021. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Ye and Wu Nanoscale Research Letters (2022) 17:1 Page 2 of 10 12]. The LCD is still the current mainstream display, but LEDs is a complicated and time-consuming task [30, 31]. its lack of self-luminosity leads to poor overall control Moreover, compared with blue and green LED chips, red efficiency with respect to the interaction of the backlight LED chips are prone to generating excessive heat due to with the liquid crystal through the color filter and two their material absorption properties, resulting in poor polarizers. This drawback has attracted much criticism photoelectric conversion efficiency and low EQE. Con - [13]. In contrast to LCDs, organic LEDs (OLEDs) display sequently, they cannot meet display requirements [32]. technology does not require a backlight and instead uses Chen et  al. applied directional control over RGB micro- a thin coating of organic light-emitting materials. The LEDs made on a 4-in patterned sapphire substrate to material of the light-emitting layer allows for the three achieve a wide color gamut of 114.4% (National Television primary colors of red, green, and blue to be produced System Committee, NTSC) and 85.4% (Rec. 2020) [33]. [14, 15]. Multiple studies have examined OLEDs display Qi et al. built a micro-LEDs array on a 0.55-in (400 × 240) technology. Ai et al. proposed an OLEDs display technol- gallium nitride substrate with a pixel density of 848 PPI ogy based on a combination of perovskite and LEDs, and and full width at half maximum (FWHM) of 18.2  nm to at an excitation wavelength of 710 nm, its external quan- produce a high-brightness, high-resolution micro-LEDs tum efficiency (EQE) reached 27% [16]. Chen et  al. pro - display [34]. The aforementioned findings indicate that posed a high-efficiency red OLEDs display with an EQE of combining blue micro-LEDs with QDs is currently the 25.2% at a peak excitation wavelength of 680 nm [17]. Hu best solution for achieving full color. Micro-LEDs have proposed a full-color blue organic LEDs with a patterned the advantages of high contrast, low power consumption, red–green quantum dots (QDs) color conversion layer long life, and fast response time, but they can be improved and achieved a color gamut standard (BT.2020) of 95% further [35]. Zhang et  al. proposed the use of pure blue with a 6.6-in full-color display [18]. In contrast to LCDs, double-shell InP/(ZnS) QDs with an emission wavelength OLEDs can emit light and do not require a backlight mod- of 468 nm and a quantum yield of 45%, and they managed ule. However, due to the characteristics of organic materi- to increase EQE by 2.8 times [36]. Yang Li et al. proposed als, a static image is prone to burn-in after a long period the application of microfluidic technology combined of use. This is the current problem that affects OLEDs with a red–green perovskite QDs color conversion layer [19, 20]. QLEDs (quantum dots light-emitting diodes) for use in micro-LEDs displays and achieved a wide color utilize QDs display technology. QDs are characterized by gamut (NTSC) of 131% [37]. Yin et al. combined CsPbBr3 wide absorption and narrow emission [21, 22]. Backlight perovskite and CdSe QDs to develop a green–red color blue LEDs produce excellent red, green, and blue light conversion layer that achieved a color gamut standard through QDs films, which provide excellent color satura - (NTSC) of 129% [38]. Shih et  al. suggested the use of tion performance. However, this technology is classified QDs composite materials in place of color filters for full- as a non-self-luminous light source technology [23, 24]. color displays and achieved 86.16% conversion efficiency Su et  al. explored the use of red, green, and blue trans- through the implementation of a QDs color conversion parent QLEDs that are built on a flexible plastic substrate layer [39]. Furthermore, current displays add a color filter and vertically integrated with UV glue. They reported to improve color purity, which absorbs most of the wave- EQE levels of 12.0%, 8.5%, and 4.5% for red, green, and length band and only allows specific wavelengths to pass. blue transparent QLEDs, respectively, demonstrating the u Th s, light extraction efficiency is substantially compro - feasibility of individually controllable RGB QLEDs [25]. mised [40–42]. Few studies have focused on improving Another predecessor of micro-LEDs technology is mini the color purity of micro-LEDs hybrid QDs. Poor color LEDs technology. The advantage of mini LEDs is their purity results in poor color saturation and reduces the small size. Ye et al. proposed a modified package structure range of the color gamut that can be displayed by a moni- for optimizing the light field type of mini LEDs, which tor. Therefore, the enhancement of color purity is crucial. can be used as a backlight source for display and lighting The present paper proposes the use of an RCPEF that [26, 27]. The Scholars have recently conducted extensive combines red and green QDs and blue micro-LEDs. This research on extremely small RGB micro-LEDs, which RCPEF only allows the light of a specific wavelength to all use inorganic semiconductor materials. The mate - pass through it, excited blue light is reflected back to the rial properties of such LEDs grant them the advantages red and green QDs layer, and the corresponding red and of photoelectric conversion efficiency, high brightness, green lights are emitted after being absorbed by the QDs, high reliability, and fast response times [28, 29]. However, thereby improving color purity and reducing absorption their application in large panel screens leads to difficul - (which leads to substantial light loss). This proposed solu - ties in performing the mass transfer and technical prob- tion meets display requirements by enabling high conver- lems relating to maintenance. When black spots or color sion efficiency and high color saturation. shifts appear on the screen, the replacement of sporadic Y e and Wu Nanoscale Research Letters (2022) 17:1 Page 3 of 10 Definition of Light Conversion Efficiency Methods Conversion efficiency refers to the ratio of effective out - Definition of Color Purity put energy to input energy. Light conversion efficiency Color purity indicates how close the color of a sample is can be obtained using Eq. (2): to its dominant wavelength spectrum and is defined as the ratio of the distance between the chromaticity coor- Area (g, r) or (G, R) dinates of the measured object and CIE1931 center ver- Light conversion efficiency := × 100% Area + Area g, r or (G, R) ( ) sus the distance between the chromaticity coordinates (2) of the standard light source and CIE1931 center. Color where Area is the total radiated power in the red and purity can be calculated using Eq.  (1). (x , y ) are the (g, r) d d green bands without RCPEF, Ar ea is the total radi- coordinates for the main wavelength spectrum’s color (G, R) ated power in the red and green bands with a layer of light source, (x , y ) are the chromaticity coordinates s s RCPEF, and Area is the total radiated power in the blue of the measured object, and (x , y ) are the chromaticity i i band (all units are in mW). coordinates for the CIE1931 center. Preparation Process for Red and Green Quantum Dots (x − x ) + y − y s i s i Color purity =  × 100 The quantum dots used in this study are red and green (1) (x − x ) + y − y CdSe/ZnS, the main reaction materials are cadmium d i d i oxide (CdO), zinc oxide (ZnO), silicon (Se), trioctyl phosphine oxide (TOP), lauric acid (LA, C H O ), 12 24 2 and n-hexane (C H ). Hexadecylamine (HDA) is used 6 14 to prevent the agglomeration reaction of QDs, metha- nol (CH OH) is used to prevent the agglomeration reaction, and argon (Ar) is used throughout the pro- cess to ensure environmental vacuum. The first part of the production process involves mixing 0.0049  g CdO, 0.0308 g ZnO, and 1.7495 g LA in a three-necked flask, then pour argon and stir the mixture with a magnet and heat it to 230  °C. After reaching 230  °C, the mix- ture was naturally cooled to 30  °C. The cooling time is used to prepare the precursor. The preparation involves injecting 0.0948 g of Se into TOP and n-hexane to form a mixture, and then shaking to completely dissolve the Fig. 1 Samples of a red and b green QDs red CdSe/ZnS emission 0.9 green CdSe/ZnS emission 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 450475 500525 550575 600625 650675 700725 750 Wavelength(nm) Fig. 2 Schematic diagram of the normalized spectral radiance of red and green CdSe/ZnS Normalized intensity (a.u.) Ye and Wu Nanoscale Research Letters (2022) 17:1 Page 4 of 10 Table 1 Specifications of red and green CdSe/ZnS samples The normalization spectral of the red and green CdSe/ZnS quantum dots are shown in Fig. 2. The emis - Red CdSe/ZnS Green CdSe/ZnS sion wavelength and FWHM of the red CdSe/ZnS Wavelength (nm) 633.5 nm 531.5 nm quantum dots are 633.5 and 41.5  nm. The emission FWHM (nm) 41.5 nm 22 nm wavelength and FWHM of the green CdSe/ZnS quan- Concentration weight (wt%) 20 wt% 20 wt% tum dots are 531.5 and 22 nm. Particle diameters (nm) 4.4 nm 3.3 nm The specifications of the red and green CdSe/ZnS QDs samples are shown in Table  1. The measurement results of the photoluminescence (PL) spectrometer show that the emission wavelength and FWHM of the Se in TOP and n-hexane. Cool the main reactant to red CdSe/ZnS QDs are 633.5 and 41.5  nm, and the 30  °C, add 3.2505  g HDA, heat the mixture to 230  °C, emission wavelength and FWHM of the green CdSe/ and heat the red QDs to 300  °C, and the green QDs to ZnS QDs are 531.5 and 22  nm. The concentration of 320  °C. Then the prepared precursor is added and the the red and green CdSe/ZnS QDs samples is 20 wt%. By reaction time is controlled. The reaction time between controlling the reaction time of the main reactant CdO the red light quantum dots and the precursor is 60  s, and the precursor Se, the particle size of the red CdSe/ and the reaction time between the green light quantum ZnS QDs is 4.4  nm and the particle size of the green dots and the precursor is 3  s. After the reaction was CdSe/ZnS QDs is 3.3 nm. completed, the mixture was quickly cooled to 150  °C, and methanol heated to about 60  °C was added to ter- RCPEF Principle and Optimal Design minate the agglomeration reaction. Finally, centrifuge We propose the use of RCPEF to achieve high color at 5000 rpm for 10 min, pour out the methanol, and air purity. When the excited blue light wavelength emitted dry. Samples of red and green QDs are shown in Fig. 1. by an LEDs passes through red and green QDs, the ina- Figure 1a shows a red light CdSe/ZnS QDs sample, and bility of the QDs to completely absorb the incident wave- Fig. 1b shows a green light CdSe/ZnS QDs sample. Both length means that the total emission wavelength is the red and green QDs are mixed in n-hexane solution. Fig. 3 RCPEF color purity improvement principle: a no RCPEF light emission, b traditional color filter architecture, and c combined RCPEF light emission architecture Y e and Wu Nanoscale Research Letters (2022) 17:1 Page 5 of 10 In the present study, Essential Macleod (Thin Film Center Inc.) simulation software was used to design the recovery of reflected color purity to enhance the film. The optimal design was achieved using the formula Air/ (HL) /SUB of the membrane stack, where L is the low refractive index material SiO , H is the high refractive index material T iO , M is the constant (i.e., the power of the membrane stack), and SUB is the substrate mate- rial (i.e., glass). The optimization calculations indicated that when M = 12, the 500 nm waveband size ripple was large and the difference between an M of 13 and 14 was Fig. 4 RCPEF bandpass film simulation small. Therefore, better results can be obtained when M = 13. The overall physical thickness was 1442.02 nm. After optimization (Fig.  4), the wavelength band was emission wavelength of the incident wavelength of the less than 470  nm for the high reflection area with a mixed QDs (Fig. 3a), which leads to poor color purity and penetration rate less than 1%, and the wavelength band color cast problems. The traditional solution is to add a was greater than 510  nm for the high penetration area color filter (CF) layer and apply the principle of material with a penetration rate greater than 92%. absorption to absorb the blue light, such that the corre- sponding green and red pixels only emit green and red light, respectively. Although a higher color purity can be Structure of High‑Color‑Purity Full‑Color Micro‑LEDs obtained, a considerable amount of energy is lost due to The processing steps and structure of high-color- material absorption as presented in Fig.  3b. To address purity full-color micro-LEDs are shown in Fig.  5. Fig- this problem in the present study, a layer of RCPEF was ure  5a shows a flexible FR4 flexible substrate. (FR-4 added above the red-green QDs of the color conver- is a composite material made from a woven fiberglass sion layer. As shown in Fig. 3c, when part of the incident cloth and epoxy resin binder.) First, blue micro-LEDs wavelength (blue light) passed through the RCPEF, the were die-bonded onto the FR4 substrate (Fig.  5b). A RCPEF reflected the blue band back to the QDs color layer of CdSe red and green QDs was then applied on conversion layer, and the red and green QDs absorbed specific pixels through dispensation (Fig.  5c, d), and again to re-excite and re-emit red and green wavelengths. a layer of RCPEF was then added above the red and After several cycles, relatively pure RGB colors were green QDs pixels (Fig. 5e). obtained. Fig. 5 Structure of high‑ color‑purity full‑ color micro‑LEDs: a flexible FR4 substrate, b die ‑bonding of blue micro ‑LEDs on FR‑4, c dispensation of red‑light QDs layer, d dispensation of green‑light QDs layer, e and completion of high‑ color‑purity full‑ color micro‑LEDs with RCPEF Ye and Wu Nanoscale Research Letters (2022) 17:1 Page 6 of 10 Fig. 6 Images of micro‑LEDs obtained using a scanning electron microscope. a top and b bottom views The normalized spectrum of the light source of the blue micro-LEDs chip is shown in Fig. 7. The wavelength peak and FWHM were 445.5 and 16 nm, and the color purity was 98.23%. Measurement Data of RCPEF Figure 8 shows the RCPEF sample and presents its meas- urement data. Figure  8a shows the sample, which meas- ures 5  cm × 5  cm. Figure  8b presents the comparison of the simulated and measured data of the RCPEF, indicat- Fig. 7 Normalized spectrum of blue micro‑LEDs chip ing a high consistency between the simulated and meas- ured transmittance rates. RCPEF for Green QDs Results and Discussion The blue micro-LEDs were converted from green QDs Blue Micro‑LEDs Chip to green light. The normalized spectrum is shown in The blue LEDs chip had a flip-chip structure, and its Fig.  9. The peak emission of green light was 531.5  nm, length, width, and height were 140, 240, and 100  μm, and the FWHM was 22 nm. Most of the light emitted at respectively. Figure  6 shows the images of the micro- this point was radiant blue light. The green light conver - LEDs that were obtained using a scanning electron sion efficiency was only 27.08%, and the color purity was microscope. 77.2%. Notably, the color purity at this point was greatly Fig. 8 RCPEF sample: a prototype sample, b measured value of penetration rate of RCPEF Y e and Wu Nanoscale Research Letters (2022) 17:1 Page 7 of 10 300350 400450 500550 600650 700750 800 300350 400450 500550 600650 700750 800 Fig. 9 Normalized blue light without RCPEF conversion to green Fig. 12 Normalized blue light without RCPEF conversion to red spectrum by QDs spectrum by QDs 100 100 80 80 60 60 40 40 300350 400450 500550 600650 700750 800 Fig. 10 Conversion of normalized blue light to a green spectrum by Fig. 13 Conversion of normalized blue light to red light by QDs after QDs after addition of RCPEF addition of RCPEF than the light conversion efficiency that was observed when the RCPEF was not used. At this point, the color purity could be increased to 97.49%. The data for the blue-to-green light conversion are shown in Fig. 11. Figure 11a shows the color of the emit- ted light without RCPEF. Because most of the emitted light was in the incident blue wavelength band, the color of the emitted light was the color mixed by the green quantum mixing incident wavelength, which led to a color shift that was similar to cyan. The addition of the RCPEF changed the color of the emitted light (Fig.  11b). Fig. 11 Green QDs sample a before and b after addition of RCPEF The part of the incident wavelength that the QDs could not absorb was reflected by the RCPEF back to the QDs layer for reabsorption and re-excitation, and it was then affected by blue light, such that the color conversion effi - radiated as green light to obtain purer green light. At this ciency, color purity, and light conversion efficiency were point, the color purity could be increased to 97.49%. not ideal and a clear color shift was observed. After the addition of the RCPEF, a normalized blue-to- RCPEF for Red QDs green spectrum was achieved (Fig.  10). The light green Blue micro-LEDs were converted into red light through emission peak was 532 nm, and the FWHM was 21 nm. red QDs. The data for the conversion of normalized blue Some incident wavelengths that could not be absorbed by light to the red light spectrum are shown in Fig.  12. The the QDs were radiated again after being reflected to the peak of red light was 633.5  nm, and the FWHM was QDs layer by the RCPEF. The light conversion efficiency 41.5 nm. Most of the emitted light was incident light blue, of green light was 53.43%, which was 1.97 times higher Ye and Wu Nanoscale Research Letters (2022) 17:1 Page 8 of 10 After the addition of the RCPEF, a normalized blue- to-red spectrum was achieved (Fig. 13). The peak emis - sion of red light was 634  nm, and the FWHM was 40.5  nm. Some incident wavelengths that could not be absorbed by the QDs were reflected by the RCPEF to the QDs layer for reabsorption, re-excitation, and re- emission as red light. The light conversion efficiency of red light was increased to 31.77%, which was 1.46 times higher than light conversion efficiency that was observed before the addition of the RCPEF, and the Fig. 14 Red QDs sample a before and b after addition of RCPEF color purity was increased to 94.68%. Figure  14 presents a practical example of the con- version of blue light to red light. Figure  14a shows the color of the emitted light before the addition of the RCPEF. Because most of the emitted light was in the incident blue light band, the light conversion efficiency for red light was only 21.78%. Therefore, the color of the obtained emitted light was red converted by mix- ing the QDs with the incident wavelength, and its color shift was similar to a magenta color. After the addition of the RCPEF, the color of the emitted light shown in Fig.  14b was achieved. Some incident wavelengths that could not be absorbed by the QDs were reflected by the RCPEF to the QDs layer to be reabsorbed and radiated as red light after excitation. A purer red light could be obtained. The color purity was increased to 94.68%. Figure  15 shows the color purity of the micro-LEDs sample. The light emitted by the sample after the addi - tion of the RCPED is shown in Fig.  15b—compared with the image in Fig. 15a, the light color of the sample exhibits purer RGB colors. Red, green, and blue color purity were 94.68%, 97.49%, and 98.23%. Fig. 15 Micro‑LEDs colors a before and b after addition of RCPEF Table  2 presents the comparison of the color purity and light conversion efficiency of blue micro-LEDs with differing configurations (i.e., with or without RCPEF and at this point, the light conversion efficiency was only and with or without red or green QDs). After the addi- 21.78%. Moreover, the color purity value was not indica- tion of the RCPEF, the color purity of red and green QDs tive because most of the wavelength band that contrib- was increased to 94.68% and 97.49%. The light conver - uted to this value was the light emitted by the incident sion efficiency of red and green QDs was increased by light-blue light and not that of the red light. Therefore, 1.46 and 1.97 times. The experimental results indicated the resulting color purity and light conversion efficiency that the combination of the blue micro-LEDs with red were not ideal, and a clear color shift phenomenon was and green QDs and the RCPEF effectively improved color observed. purity and light conversion efficiency. Table 2 Comparison of blue micro‑LEDs with differing configurations Type Only blue micro‑LEDs Blue micro‑LEDs with G‑ QDs Blue micro‑LEDs with R‑ QDs RCPEF Without filter Without RCPEF With RCPEF Without RCPEF With RCPEF Light conversion efficiency (%) 100% 27.08% 53.43% 21.78% 31.77% Peak wavelength (nm) 445.5 nm 531.5 nm 532 nm 633.5 nm 634 nm FWHM (nm) 16 nm 22 nm 21 nm 41.5 nm 40.5 nm Y e and Wu Nanoscale Research Letters (2022) 17:1 Page 9 of 10 Received: 15 August 2021 Accepted: 16 December 2021 Conclusions This research suggests that combining blue micro- LEDs with red and green QDs and a layer of RCPEF can improve color purity and light conversion efficiency. The References incident blue-light wavelengths that cannot be com- 1. Chen HW, Lee JH, Lin BY, Chen S, Wu ST (2018) Liquid crystal display and pletely absorbed by the QDs are reflected to the color organic light‑ emitting diode display: present status and future perspec‑ tives. Light Sci Appl 7:17168. https:// doi. org/ 10. 1038/ lsa. 2017. 168 conversion layer. Subsequently, they are reabsorbed 2. Huang Y, Hsiang EL, Deng MY, Wu ST (2020) Mini‑LED, Micro ‑LED and by red and green QDs for re-excitation and radiation, OLED displays: present status and future perspectives. Light Sci Appl thereby achieving high color purity and high conversion 9:105. https:// doi. org/ 10. 1038/ s41377‑ 020‑ 0341‑9 3. Qi Y, Xiao X, Lu Y, Shu J, Wang J, Chen M (2019) Cathode ray tubes glass efficiency. Thus, the problem of poor color purity in color recycling: a review. Sci Total Environ 650(Pt 2):2842–2849. https:// doi. org/ conversions between micro-LEDs and QDs is alleviated. 10. 1016/j. scito tenv. 2018. 09. 383 Furthermore, because RCPEF is a type of feedback 4. Desroches L‑B, Ganeshalingam M (2015) The dynamics of incremental costs of efficient television display technologies. Technol Forecast Soc reflection, conversion efficiency can be improved. The Change 90:562–574. https:// doi. org/ 10. 1016/j. techf ore. 2014. 02. 016 prototype experimental data indicate that with the addi- 5. Lin C‑H (2006) Digital‑ dimming controller with current spikes elimination tion of an RCPEF layer, the color purity of the red and technique for LCD backlight electronic ballast. IEEE Trans Ind Electron 53(6):1881–1888. https:// doi. org/ 10. 1109/ tie. 2006. 885143 green quantum dots increased to 94.68% and 97.49%, 6. Hong T‑ Y, Chien C‑F (2020) A simulation‑based dynamic scheduling and respectively, and the light conversion efficiency of the red dispatching system with multi‑ criteria performance evaluation for Indus‑ and green quantum dots increased by 1.46 times and 1.97 try 3.5 and an empirical study for sustainable TFT‑LCD array manufactur ‑ ing. Int J Prod Res 58(24):7531–7547. https:// doi. org/ 10. 1080/ 00207 543. times, respectively. The addition of the RCPEF effectively 2020. 17773 42 improves the color purity and light conversion efficiency 7. Wu C, Wang X, Lin L, Guo H, Wang ZL (2016) Paper‑based triboelectric of light such that micro-LEDs displays can achieve higher nanogenerators made of stretchable interlocking Kirigami patterns. ACS Nano 10(4):4652–4659. https:// doi. org/ 10. 1021/ acsna no. 6b009 49 color saturation and light output efficiency, thus enhanc - 8. Yuan F, He P, Xi Z, Li X, Li Y, Zhong H, Fan L, Yang S (2019) Highly efficient ing their display specifications and commercial value. In and stable white LEDs based on pure red narrow bandwidth emission the future, the application of micro-patterning in ultra- triangular carbon quantum dots for wide‑ color gamut backlight displays. Nano Res 12(7):1669–1674. https:// doi. org/ 10. 1007/ s12274‑ 019‑ 2420‑x high-pixel micro-LEDs displays can be further examined. 9. Chen H, Zhu R, Tan G, Li MC, Lee SL, Wu ST (2017) Enlarging the color gamut of liquid crystal displays with a functional reflective polarizer. Opt Express 25(1):102–111. https:// doi. org/ 10. 1364/ OE. 25. 000102 Abbreviations 10. Lee TX, Chen BS (2016) High uniformity and tolerance design for direct‑lit B: Blue; CF: Color filter; CRT : Cathode ray tube; EQE: External quantum effi‑ LED backlight illumination using lagrange interpolation (in English). J ciency; FWHM: Full width at half maximum; G: Green; HDA: HEXADECYL amine; Disp Technol 12(11):1403–1410. https:// doi. org/ 10. 1109/ jdt. 2016. 26066 49 LA: Lauric acid; LCD: Liquid–crystal display; LEDs: Light‑ emitting diodes; NTSC: 11. Oh JH, Kang H, Ko M, Do YR (2015) Analysis of wide color gamut of green/ National television system committee; OLEDs: Organic light‑ emitting diode; red bilayered freestanding phosphor film‑ capped white LEDs for LCD QDs: Quantum dots; QDF: Quantum dots film; QLEDs: Quantum dots light ‑ backlight. Opt Express 23(15):A791‑804. https:// doi. org/ 10. 1364/ OE. 23. emitting diodes; R: Red; RCPEF: Reflection color purity enhancement film; SEM: 00A791 Scanning electron microscope; TOP: Trioctylphosphine; W: White. 12. Chen H‑ W, Zhu R‑D, He J, Duan W, Wei Hu, Yan‑ Qing Lu, Li M‑ C, Lee S‑L, Dong Y‑ J, Shin‑ Tson Wu (2017) Going beyond the limit of an LCD’s color Acknowledgements gamut. Light Sci Appl 6(9):e17043. https:// doi. org/ 10. 1038/ lsa. 2017. 43 This research was supported by the Ministry of Science and Technology, 13. Chen H, Zhu R, Li MC, Lee SL, Wu ST (2017) Pixel‑by‑pixel local dimming the Republic of China (Grant No. MOST 110‑2221‑E‑194‑036 and MOST for high‑ dynamic‑range liquid crystal displays. Opt Express 25(3):1973– 110‑2622‑E‑194‑007). 1984. https:// doi. org/ 10. 1364/ OE. 25. 001973 14. Song J, Lee H, Jeong EG, Choi KC, Yoo S (2020) Organic light‑ Authors’ Contributions emitting diodes: pushing toward the limits and beyond. Adv Mater ZTY designed the experiments. J‑ YW analyzed data. ZTY and J‑ YW discussed 32(35):e1907539. https:// doi. org/ 10. 1002/ adma. 20190 7539 the results and contributed to the writing of the manuscript. Both authors 15. Wang S, Zhang H, Zhang B, Xie Z, Wong W‑ Y (2020) Towards high‑power ‑ read and approved the final manuscript. efficiency solution‑processed OLEDs: material and device perspectives. Mater Sci Eng R Rep. https:// doi. org/ 10. 1016/j. mser. 2020. 100547 Funding 16. Ai X, Evans EW, Dong S, Gillett AJ, Guo H, Chen Y, Hele TJ, Friend RH, This work was financially/partially supported by the Advanced Institute of Li F (2018) Efficient radical‑based light ‑ emitting diodes with dou‑ Manufacturing with High‑ Tech Innovations from the Featured Areas Research blet emission. Nature 563(7732):536–540. https:// doi. org/ 10. 1038/ Center Program within the framework of the Higher Education Sprout Project s41586‑ 018‑ 0695‑9 by the Ministry of Education in Taiwan. 17. Chen JX, Tao WW, Chen WC, Xiao YF, Wang K, Cao C, Yu J, Li S, Geng FX, Adachi C, Lee CS (2019) Red/near‑infrared thermally activated delayed Available of Data and Materials fluorescence OLEDs with near 100% internal quantum efficiency. Angew The datasets supporting the conclusions of this article are available in the Chemie 131(41):14802–14807. https:// doi. org/ 10. 1002/ anie. 20190 6575 article. 18. Hu Z, Yin Y, Ali MU, Peng W, Zhang S, Li D, Zou T, Li Y, Jiao S, Chen SJ, Lee CY (2020) Inkjet printed uniform quantum dots as color conversion layers Declaration for full‑ color OLED displays. Nanoscale 12(3):2103–2110. https:// doi. org/ 10. 1039/ c9nr0 9086j Competing interests 19. Xu Z, Gu J, Qiao X, Qin A, Tang BZ, Ma D (2019) Highly efficient deep blue The authors declare that they have no competing interests. aggregation‑induced emission organic molecule: a promising multifunc‑ tional electroluminescence material for blue/green/orange/red/white Ye and Wu Nanoscale Research Letters (2022) 17:1 Page 10 of 10 OLEDs with superior efficiency and low roll‑ off. ACS Photon 6(3):767–778. 38. Yin Y, Hu Z, Ali MU, Duan M, Gao L, Liu M, Peng W, Geng J, Pan S, Wu https:// doi. org/ 10. 1021/ acsph otoni cs. 8b017 24 Y, Hou J (2020) Full‑ color micro‑LED display with CsPbBr 3 perovskite 20. Pang Z, Sun D, Zhang C, Baniya S, Kwon O, Vardeny ZV (2017) Manipula‑ and CdSe quantum dots as color conversion layers. Adv Mater Technol tion of emission colors based on intrinsic and extrinsic magneto‑ electro‑ 5(8):2000251. https:// doi. org/ 10. 1002/ admt. 20200 0251 luminescence from exciplex organic light‑ emitting diodes. ACS Photon 39. Shih YC, Shi FG (2017) Quantum dot based enhancement or elimina‑ 4(8):1899–1905. https:// doi. org/ 10. 1021/ acsph otoni cs. 7b005 67 tion of color filters for liquid crystal display. IEEE J Sel Top Quant Electron 21. Chen LC, Tien C‑H, Chen DF, Kuo HC, Ye ZT (2019) High‑uniformity 23(5):1–4. https:// doi. org/ 10. 1109/ jstqe. 2017. 27489 23 planar mini‑ chip‑scale packaged LEDs with quantum dots converter 40. Ma Y, Xin SJ, Liu X, Liu Y, Sun J, Wang X, Guo Q, Chigrinov VG (2020) for white light source. Nanoscale Res Lett. https:// doi. org/ 10. 1186/ Colour generation for optically driving liquid crystal display. Liq Crystals s11671‑ 019‑ 2993‑z 47(12):1729–1734. https:// doi. org/ 10. 1080/ 02678 292. 2020. 17215 80 22. Won Y‑H, Cho O, Kim T, Chung D ‑ Y, Kim T, Chung H, Jang H, Lee J, Kim D, 41. Itoh Y, Langlotz T, Iwai D, Kiyokawa K, Amano T (2019) Light attenuation Jang E (2019) Highly efficient and stable InP/ZnS/ZnS quantum dot light ‑ display: subtractive see‑through near ‑ eye display via spatial color filter ‑ emitting diodes. Nature 575(7784):634–638. https:// doi. org/ 10. 1038/ ing. IEEE Trans Vis Comput Graph 25(5):1951–1960. https:// doi. org/ 10. s41586‑ 019‑ 1771‑51109/ TVCG. 2019. 28992 29 23. Lan X, Chen M, Hudson MH, Kamysbayev V, Wang Y, Guyot‑Sionnest 42. Ji C, Lee KT, Xu T, Zhou J, Park HJ, Guo LJ (2017) Engineering light at the P, Talapin DV (2020) Quantum dot solids showing state‑resolved nanoscale: structural color filters and broadband perfect absorbers. Adv band‑like transport. Nat Mater 19(3):323–329. https:// doi. org/ 10. 1038/ Opt Mater. https:// doi. org/ 10. 1002/ adom. 20170 0368 s41563‑ 019‑ 0582‑2 24. Keum H, Jiang Y, Park JK, Flanagan JC, Shim M, Kim S (2018) Photoresist Publisher’s Note contact patterning of quantum dot films. ACS Nano 12(10):10024–10031. Springer Nature remains neutral with regard to jurisdictional claims in pub‑ https:// doi. org/ 10. 1021/ acsna no. 8b044 62 lished maps and institutional affiliations. 25. Su Q, Zhang H, Chen S (2021) Flexible and tandem quantum‑ dot light‑ emitting diodes with individually addressable red/green/blue emission. npj Flexible Electron. https:// doi. org/ 10. 1038/ s41528‑ 021‑ 00106‑y 26. Ye ZT, Ruan MJ, Kuo HC (2020) CSP‑leds combined with light guide with‑ out reflective matrix for antiglare design. IEEE Access 8:156718–156726. https:// doi. org/ 10. 1109/ access. 2020. 30193 14 27. Ye ZT, Chang C, Juan MC, Chen KJ (2020) luminous intensity field optimi‑ zation for antiglare LED desk lamp without second optical element. Appl Sci Basel 10(7):13. https:// doi. org/ 10. 3390/ app10 072607 28. Lee HE et al (2019) Wireless powered wearable micro light‑ emitting diodes. Nano Energy 55:454–462. https:// doi. org/ 10. 1016/j. nanoen. 2018. 11. 017 29. Kim K, Voroslakos M, Seymour JP, Wise KD, Buzsaki G, Yoon E (2020) Artifact‑free and high‑temporal‑resolution in vivo opto ‑ electrophysiology with microLED optoelectrodes. Nat Commun 11(1):2063. https:// doi. org/ 10. 1038/ s41467‑ 020‑ 15769‑w 30. Xuan T, Shi S, Wang L, Kuo HC, Xie RJ (2020) Inkjet‑printed quantum dot color conversion films for high‑resolution and full‑ color micro light‑ emitting diode displays. J Phys Chem Lett 11(13):5184–5191. https:// doi. org/ 10. 1021/ acs. jpcle tt. 0c014 51 31. Pan Z, Guo C, Wang X, Liu J, Cao R, Gong Y, Wang J, Liu N, Chen Z, Wang L, Ishikawa M (2020) Wafer‑scale micro ‑LEDs transferred onto an adhesive film for planar and flexible displays. Adv Mater Technol 5(12):200549. https:// doi. org/ 10. 1002/ admt. 20200 0549 32. Yuan Z, Shujie G, Xia Mao Gu, Simin ZY, Xianbo Wu, Jing W, Nan Z, Zhi Z (2019) Enhancing quantum efficiency and tuning photoluminescence properties in far‑red‑ emitting phosphor Ca14Ga10Zn6O35:Mn4+ based on chemical unit engineering. Chem Eng J 374:381–391. https:// doi. org/ 10. 1016/j. cej. 2019. 05. 201 33. Chen SW, Huang YM, Singh KJ, Hsu YC, Liou FJ, Song J, Choi J, Lee PT, Lin CC, Chen Z, Han J (2020) Full‑ color micro‑LED display with high color sta‑ bility using semipolar (20–21) InGaN LEDs and quantum‑ dot photoresist. Photon Res 8(5):630–636. https:// doi. org/ 10. 1364/ prj. 388958 34. Qi L, Zhang X, Chong WC, Li P, Lau KM (2021) 848 ppi high‑brightness active‑matrix micro ‑LED micro ‑ display using GaN‑ on‑Si epi‑ wafers towards mass production. Opt Express 29(7):10580–10591. https:// doi. org/ 10. 1364/ OE. 419877 35. Zhou X, Tian P, Sher CW, Wu J, Liu H, Liu R, Kuo HC (2020) Growth, transfer printing and colour conversion techniques towards full‑ colour micro‑LED display. Prog Quant Electron 1(71):100. https:// doi. org/ 10. 1016/j. pquan telec. 2020. 100263 36. Zhang W, Ding S, Zhuang W, Wu D, Liu P, Qu X, Liu H, Yang H, Wu Z, Wang K, Sun XW (2020) InP/ZnS/ZnS core/shell blue quantum dots for efficient light‑ emitting diodes. Adv Funct Mater 30(49):2005303. https:// doi. org/ 10. 1002/ adfm. 20200 5303 37. Li Y, Tao J, Wang Q, Zhao Y, Sun Y, Li P, Lv J, Qin Y, Wang W, Zeng Q, Liang J (2021) Microfluidics‑based quantum dot color conversion layers for full‑ color micro‑LED display. Appl Phys Lett 118(17):173501. https:// doi. org/ 10. 1063/5. 00478 54

Journal

Nanoscale Research Letters – Springer Journals

Published: Jan 3, 2022

Keywords: Micro-LEDs; Quantum dots; Color purity; Recycling-reflection color-purity-enhancement film; Light conversion efficiency

There are no references for this article.