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- Hindawi Publishing Corporation
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- Copyright © 2007 Ju H. Choi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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- 10.1155/2007/39892
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Abstract
Hindawi Publishing Corporation Advances in OptoElectronics Volume 2007, Article ID 39892, 8 pages doi:10.1155/2007/39892 Research Article 3+ Fluorescence and Nonradiative Properties of Nd in Novel Heavy Metal Contained Fluorophosphate Glass 1 2 2 1 3 Ju H. Choi, Alfred Margaryan, Ashot Margaryan, Frank G. Shi, and Wytze Van Der Veer Department of Chemical Engineering and Materials Science, University of California, Irivne, CA 92697, USA AFO Research Inc., P.O. Box 1934, Glendale, CA 91209, USA Department of Chemistry, University of California, Irvine, CA 92697, USA Received 15 November 2006; Accepted 18 February 2007 Recommended by Jongha Moon We demonstrate new series of heavy metal containing fluorophosphate glass system. The fluorescence and nonradiative properties 3+ of Nd ions are investigated as a function of Nd O concentration. The variation of intensity parameters Ω , Ω ,and Ω is 2 3 2 4 6 determined from absorption spectra. The spontaneous probability (A) and branching ratio (β) are determined using intensity 4 4 parameters. The emission cross sections for the F → I transition, which is calculated by Fuchtbabauer-Ladenburg method, 3/2 13/2 −21 −21 2 4 4 −20 decrease from 6.1 × 10 to 3.0 × 10 (pm ) and those for the F → I transition decrease from 3.51 × 10 to 1.7 × 3/2 11/2 −20 10 as Nd O concentration increase up to 3 wt%. The nonradiative relaxation is analyzed in terms of multiphonon relaxation 2 3 3+ and concentration quenching due to energy transfer among Nd ions. Finally, the above results obtained at 1 wt% Nd O are 2 3 compared with some of reported laser host glasses which indicated the potentials for broadband-amplifiers and high-power laser applications. Copyright © 2007 Ju H. Choi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. INTRODUCTION Those advantages can represent one of the best potential host materials for several rare earth dopants for laser appli- Over the past several decades, optical and spectroscopic cations [9–11]. Typically, heavy metal contained glasses have been used for nonlinear photonic devices such as switch- properties of various trivalent lanthanides have been exten- inhg. The efforts to improve quantum efficiency of the lu- sively investigated for various host materials to apply opti- minescence bands have paid attention to heavy metal con- cal devices. Among many trivalent lanthanides, researches 3+ 3+ tained host materials as well as active ion concentration. The on Nd -doped glasses have been performed because Nd - host glass materials should also have high refractive index doped fiber has attracted much interest for optical ampli- with good chemical and thermal stability along with low fier at the region around 1325 nm with the rapid develop- melting temperature of heavy metals in order to become ment of telecommunications as well as around 1050 nm for more practical usage in industry. Spectroscopic and opti- high-power laser applications [1–3]. In general, the optical and spectroscopic properties are strongly dependent on host cal properties based on fluorophosphates glass doped with 3+ 3+ Yb and Nd were successfully investigated and presented materials. Many potential host materials for rare earth ions have been developed. Among them, fluorophosphates glasses strong potentials as gain medium in our previous works [12– 15]. show outstanding advantages such as low phonon energy, transmittance from UV to IR spectral range, and low nonlin- The purpose of this paper is to introduce the up- graded fluorophosphates glasses by including the heavy ear refractive index [4–6]. It was also found that with a flu- metal contained phosphate compositions. The newly devel- orophosphate glass, a relatively higher degree of line broad- − − − oped Bi(PO ) Ba(PO ) BaF MgF glass system (BBBM ening and smoother line shapes can be obtained [7]. It was 3 3 3 2 2 2 3+ system) with different amounts of Nd O have been sys- also observed that Nd -doped fluorophosphate glasses can 2 3 tematically investigated on spectroscopic properties. Inten- deliver relatively shorter pulses than pure phosphate glasses, sity parameters, emission cross section, radiative lifetime, which were attributed to the relatively higher degree of inho- branching ration, and fluorescence quantum efficiency are mogeneous line broadening in fluorophosphate glasses [8]. 2 Advances in OptoElectronics Table 1: Values of reduced matrix elements for the chosen emission determined from the absorption and the emission spectra us- 3+ of Nd in Bi(PO ) −Ba(PO ) −BaF −MgF glass systems. 3 3 3 2 2 2 ing Judd-Ofelt parameter theory. The trend of spectroscopic 4 4 4 4 properties between the F → I and the F → I 3/2 13/2 3/2 11/2 4 (2) 2 (4) 2 (6) 2 Transition from F λ (nm) [U ] [U ] [U ] 3/2 areinvestigatedasafunction of Nd O . 2 3 I 1824 0 0 0.0280 15/2 I 1324 0 0 0.2120 2. EXPERIMENTS AND DATA ANALYSIS 13/2 I 1054 0 0.142 0.4070 11/2 2.1. Glass synthesis and measurements I 899 0 0.23 0.056 9/2 Starting materials from reagent grade (city chemicals) and Nd O (spectrum materials) have above 99.99% purity. A se- 2 3 2 2 3 n(n +2) /9and χ = n are local field corrections and MD ries of glasses were weighed on 0.001% accuracy according are functions of the medium refractive index n. S is the ED to mole ratio (20Bi(PO ) −10Ba(PO ) −35BaF −35MgF ) 3 3 3 2 2 2 electrical dipole line strength, respectively, and is given by and mixed thoroughly. The raw mixed materials were melted in a vitreous carbon crucible in Ar-atmosphere at 1200– 2 N (t) N S (aJ , bJ ) = e Ω 4 f aJ U 4 f bJ ,(2) 1250 C. The quenched samples were annealed at transition ED t ◦ t=2,4,6 temperature below 50–100 C to remove an internal stress. The residual stress was examined by the polariscope (rudolph where the reduced matrix elements of the unit tensor oper- instruments). Samples for optical and spectroscopic mea- (t) ators, U , are calculated in the intermediate-coupling surements were cut and polished by the size of 15 × 10 approximation. They are found to be almost invariant to the × 2mm . The refractive index of the samples was mea- environment and are given by Carnall et al. [18]. The val- sured using an Abbe refractometer (ATAGO). The absorp- ues of reduced matrix elements and the mean wavelength of tion spectra were recorded at room temperature in the range 3+ the chosen emission bands of Nd were tabulated in Table 1. of 400–1700 nm with a Perkin-Elmer photo spectrometer The measured oscillator strengths f at each absorption med (Lambda 900). The resolution is set to 1 nm. Emission spec- wavelength can be calculated from the integrated optical ab- tra are obtained by exciting the samples with 808 nm radi- sorption spectra and are given by following expression from ation from a CW laser diode (coherent). The fluorescence radiation is then recorded over the range 850–1400 nm us- mc α(λ) ing a monochromator (Acton SpectraPro 300) and a ge- f = dλ,(3) med 2 2 πe N λ photodiode (Thorlabs). The laser radiation incident to the sample is passed through an optical chopper (Stanford Re- 3+ where c is light velocity, N is the Nd ion concentration search) enabling the use of a lock-in amplifier (Ametek 5105) (ion/cm ). α(λ)(= 2.303D (λ)/d) is the measured optical to recover and amplify the electronic signal from the detec- absorption coefficient at a particular absorption wavelength tor. The lifetime of the excited state is determined with a Q- λ and d is the sample thickness. switched Nd:YAG laser pumping an OPO (continuum sure- The oscillator strengths both experimentally and theoret- lite) tuned to 808 nm (idler). The duration of the pulses is ically obtained are presented in Table 2.Inorder to evaluate 5 nanoseconds. The fluorescent radiation is detected using a the validity of the intensity parameters, the deviation param- Si pin photodiode (Thorlabs) and an interference filter (Ed- eter was obtained by the root-mean-square (rms, δ ) rms mund Scientific). The signal is recorded with a fast oscillo- scope (LeCroy 9350) and fitted to an exponential. f − f cal med δ = ,(4) rms N − N par trans 2.2. Judd-Ofelt theory where N is the number of spectral bands analyzed and par Judd-Ofelt theory has been used to investigate radiative na- N are 3 in this case, which is the parameter number trans ture of trivalent rare earth ions in a variety of laser host ma- −6 sought. The values of δ within 5× 10 imply the good fit- rms terials [16, 17]. The absorption spectra of rare earth ions of ting between the measured f and the theoretical f oscil- med cal 4 f -4 f electronic transitions are from electric dipole, mag- lator strengths. These Judd-Ofelt parameters obtained from netic dipole, and electric quadrupole. The intensity parame- the fitting between the measured f and the theoretical f med cal ter, radiative lifetime, and branching ratio are calculated with oscillator strengths can be also applied to calculate the line refractive index using Judd-Ofelt analysis. The theoretical os- strength corresponding to the transitions from the initial J cillator strengths f are derived by using the Judd-Ofelt the- cal manifold and the final J manifold. ory. Theoretical oscillator strengths f (aJ , bJ ) of the J → J The radiative transition probabilities given in (5)were transition at the mean frequency ν are given for an electric 4 4 obtained with the line strength for the excited F to I 3/2 J and magnetic dipole transition by 4 4 4 3+ manifold ( I , I ,and I )for Nd : 9/2 11/2 13/2 8π mν f (aJ , bJ ) = χ S (aJ , bJ ) ,(1) cal ED ED 2 2 4 2 3(2J +1)he n 64π n n +2 A [aJ , bJ ] = S (aJ , bJ ) , rad ED 3h(2J +1)λ 9 where m is the mass of the electron, e and h are the charge (5) of the electron and Plank’s constant, respectively. χ = ED Ju H. Choi et al. 3 6 3+ Table 2: Experimental and calculated oscillator strengths ( f × 10 )ofNd in 20Bi(PO ) −10Ba(PO ) −35BaF −35MgF glass system at 3 3 3 2 2 2 room temperature. Transition 0.5 wt% 1wt% 1.5 wt% 3wt% −1 Energy (cm ) from I 9/2 f f f f f f f f med cal med cal med cal med cal F 11442 1.71 3.45 2.52 3.24 2.20 3.21 1.17 1.58 3/2 F 12469 8.10 9.27 8.55 8.64 8.24 8.75 4.33 4.46 5/2 F 13405 9.05 8.80 8.05 8.17 8.46 8.38 4.35 4.35 7/2 F 14684 1.13 0.72 0.53 0.67 0.55 0.68 0.20 0.35 9/2 G 17182 19.12 19.20 16.48 16.53 17.20 17.25 8.83 8.84 5/2 G 19048 8.81 7.37 7.16 6.79 7.88 6.85 3.78 3.44 7/2 K 21008 5.33 1.75 3.19 1.64 3.08 1.64 1.48 0.82 15/2 P 23310 0.53 0.96 0.35 0.90 0.21 0.89 0.15 0.43 1/2 3+ Table 3: Theoretically calculated radiation transition probability, branching ratios radiative lifetime, and quantum efficiency of Nd in − − − 20Bi(PO ) 10Ba(PO ) 35BaF 35MgF glasssystematroomtemperature. 3 3 3 2 2 2 0.5 wt% 1.0 wt% 1.5 wt% 3wt% 4 −1 Transitions from F Energy (cm ) 3/2 A β A β A β A β −1 −1 −1 −1 (s ) (%) (s ) (%) (s ) (%) (s ) (%) I 7508 358 8.5 333 8.4 343 8.6 179 8.9 13/2 I 9443 1948 46.1 1817 45.9 1849 46.4 946 47.1 11/2 I 11186 1922 45.5 1808 45.7 1796 45.0 884 44.0 9/2 −1 A = A (s ) 4229 3958 3989 2009 τ (μs) 237 253 251 498 rad Quantum efficiency 76% 67% 62% 30% 2 2 3+ where n(n +2) /9 is the local field correction for Nd in the where λ is the wavelength of the peak emission, c is the initial J manifold. J is the final manifold. n is the refractive speed of light in vacuums, and n(λ ) is the refractive in- index at the wavelength of the transition. dex at each emission peak wavelength. Δλ is an effective eff The emission branching ratio for transitions originat- linewidth. Since the emission band is asymmetry, it is used ing from initial manifold can be obtained from the radiative instead of the full width at half maximum linewidth. It is transition probabilities A by using characterized in the name of an effective linewidth as follows: rad 4 4 I (λ)dλ A F −→ I 3/2 J 4 4 Δλ = . (8) eff β F −→ I = ,(6) 3/2 J 4 4 max A F −→ I 3/2 J I is the maximum intensity at fluorescence emission max where the summation is over all terminal manifolds. Theo- 3+ peaks. retically computed radiative properties of Nd in the current system including radiative transition probabilities, branch- ing ratio ratios radiative lifetime and quantum efficiency are 3. RESULTS AND DISCUSSION listed in Table 3. 3.1. Absorption spectra analysis 2.3. Stimulated emission cross-section The absorption spectra BBBM system doped with 3 wt% Nd O recorded in the 400–950 nm at room temperature Laser transitions are also characterized by stimulated emis- 2 3 3+ are shown in Figure 1. The absorption spectra of Nd ions sion cross sections while the induced emission cross sec- in BBBM system are corresponding to transitions from the tions are characterized by Judd-Ofelt theory. The stimu- 4 4 ground state I to various excited states within the 4 f shell. 9/2 lated emission cross-section between I → I is given by J J The appropriate electronic transitions were assigned to these Fuchtbabauer-Ladenburg method [19]: bands. The integrated area of the absorption band of the 4 4 2 4 I → ( F + H ) transition linearly increased and the re- 9/2 5/2 9/2 σ = A(aJ , bJ ), (7) fractive indices (n ) increase from 1.6263 to 1.6355 in BBBM em D 8πcn λ Δλ p eff system as Nd O concentration increases up to 3 wt%. 2 3 4 Advances in OptoElectronics −4 ×10 1.2 I → lower level 9/2 0.8 0.6 0.4 0.2 400 500 600 700 800 900 2 3 4 567 8 −4 ×10 Wavelength (nm) Fluorescence decay lifetime (s) 3wt% Nd O 2 3 1.5wt% Nd O 2 3 1wt% Nd O 2 3 3+ Figure 1: Absorption spectra of 3 wt% Nd doped Bi(PO ) – 3 3 0.5wt% Nd O 2 3 Ba(PO ) −BaF −MgF glasssystematroomtemperature. 3 2 2 2 3+ 4 4 Figure 3: Fluorescence decay curves of Nd for the F → I 3/2 11/2 transition at room temperature as a function of concentration in −5 ×10 − − − the Bi(PO ) Ba(PO ) BaF MgF glass system. 3 3 3 2 2 2 1wt% Nd O 2 3 1.8 Pumping power concentration. There is a linear decrease from 180 to 157 μs 1.6 700 mW in fluorescence decay rate by measuring lifetime of the F 3/2 1.4 600 mW level as Nd O concentration increases up to 1.5 wt%. 2 3 500 mW 1.2 400 mW 300 mW 4. DISCUSSION 200 mW 0.8 100 mW 4.1. Dependence of intensity parameters on 0.6 Nd O concentration 2 3 0.4 The best set of Ω parameters was determined by a standard 0.2 least-square fitting of the theoretical oscillator strength val- ues to the measured ones. The variation of Judd-Ofelt pa- 3+ 900 1000 1100 1200 1300 1400 rameters Ω for Nd ions in the BBBM system is shown Wavelength (nm) as a function of Nd O in Figure 4. The intensity param- 2 3 3+ −20 eter Ω for Nd slightly decreases from 2.54 × 10 to −20 2 1.12 × 10 (pm ) with increase in Nd O concentration. Figure 2: Emission spectra of 1.0 wt% Nd O doped Bi(PO ) – 2 3 2 3 3 3 3+ Ba(PO ) −BaF −MgF glass system as a function of pumping The intensity parameters Ω ,and Ω for Nd are also 4 6 3 2 2 2 −20 −20 power. found to decrease from 6.86 × 10 to 3.09 × 10 and −20 −20 2 5.74 × 10 to 2.87 × 10 (pm ), respectively, with in- crease in Nd O concentration from 0.5 wt% to 3 wt%. For 2 3 − − − Bi(PO ) Ba(PO ) BaF MgF systems, the trend for the 3 3 3 2 2 2 3.2. Fluorescence spectra analysis Ω parameters is Ω < Ω < Ω . The tendency of intensity t 2 6 4 Figure 2 shows the measured emission spectra of 1.0 wt% parameters is in agreement with those reported by Kumar et Nd O doped BBBM system. Using the excitation wave- al. [20] and comparable with those of other fluorophosphates 2 3 length of 808 nm, emission spectra were recorded at room glasses [21, 22]. temperature in the range of 750 nm to 1600 nm. Three emis- It is well known that the parameter Ω exhibits the de- sion spectra, which are centered at 876, 1058, and 1334 nm, pendence on the covalency between rare earth ions and lig- present broad bands, which is well known that it is character- ands anions, since Ω reflects the asymmetry of the local 3+ istic because of the inhomogeneous disordered glasses. The environment at the Nd ion site [23]. The relatively small −20 2 fluorescence intensities also increase as the pumping power value of Ω (below 2.0 × 10 pm ) exhibits the covalence increases. Figure 3 shows the fluorescence decay lifetime of in bonding [24]. In addition, the slight decrease of Ω with 3+ 4 4 Nd for the F → I transition as a function of Nd O an increase in Nd O concentration indicates the decrease of 3/2 11/2 2 3 2 3 Intensity (a.u.) Absorption intensity (a.u.) 4 4 ( D + D ) 3/2 5/2 1/2 2 4 2 2 ( G + G + K + D ) 9/2 11/2 15/2 3/2 4 2 ( G + G ) 5/2 7/2 11/2 9/2 4 4 ( F + S ) 7/2 3/2 4 2 ( F + H ) 5/2 9/2 3/2 Fluorescence intensity (a.u.) Ju H. Choi et al. 5 −20 ×10 1.22 1.2 1.18 1.16 1.14 1.12 1.1 1.08 1 1.06 0.51 1.52 2.53 24 6 Nd O concentration (wt%) 2 3 Judd-Ofelt intensity parameters Nd O concentration 2 3 Figure 5: Dependence of the spectroscopic quality factor (η)asa function of Nd O concentration in the Bi(PO ) −Ba(PO ) –BaF 0.5wt% 1.5wt% 2 3 3 3 3 2 2 MgF glass system. 1wt% 2 3wt% 3+ Figure 4: Variation of Judd-Ofelt parameters, Ω ,for Nd ions as a function of Nd O in the Bi(PO ) −Ba(PO ) −BaF −MgF glass 2 3 3 3 3 2 2 2 0.5 system. 0.45 covalency. Emission intensity could be also uniquely char- acterized by the Ω and Ω parameters because Ω is not 4 6 2 included to calculate branching ration for the laser F → 3/2 0.4 I transition. It is called spectroscopic quality factor χ 11/2 (= Ω /Ω ) suggested by Jacobs and Weber [25]. 4 6 0.1 4.2. Dependence of spectroscopic quality factor and branching ratio on Nd O concentration 2 3 Figure 5 shows the dependence of the spectroscopic quality 0.05 factor χ as a function of Nd O concentration. χ is found 2 3 0.51 1.52 2.53 to increase from 1.19 to 1.21 at 1 wt% Nd O and then de- 2 3 Nd O concentration (wt%) 2 3 crease 1.07 with increase in Nd O concentration. Usually, 2 3 3+ χ is in the range from 0.22 to 1.5 for Nd in several host I 13/2 materials [21]. For the relationship between the variation of 11/2 4 4 4 4 χ and the F → I and F → I transition, it is 3/2 11/2 3/2 9/2 9/2 reported that in the case of Ω ≥ Ω , the efficiency of the 4 6 4 4 F → I transition is reduced and on the other hand the 3/2 11/2 Figure 6: Variation of branching ratio (β) as a function of Nd O 4 4 2 3 efficiency of the F → I transition is enhanced, for ex- 3/2 9/2 − − − concentration in the Bi(PO ) Ba(PO ) BaF MgF glass sys- 3 3 3 2 2 2 ample, on the other hand, the smaller the value of χ, the more tem. 4 4 intense the laser F → I transition [26, 27]. Figure 6 3/2 11/2 shows the variation of branching ratio (β) with as a func- tion of Nd O concentration. It is observed that the values of 2 3 4 4 β for the F → I transition slightly increase from 0.45 3/2 9/2 to 0.46 at 1 wt% and then decrease 0.44 at 3 wt%. Those of in Nd O concentration. Similar values (≈ 0.46) compared 2 3 4 4 branching ratio for the F → I transition will show to other fluorophosphate glasses have been obtained, which 3/2 11/2 4 4 the opposite trends compared to the F → I transition. indicated also the potentials for laser host materials for the 3/2 9/2 4 4 It slightly decreases to 0.459 at 1 wt% and then increases to F → I transitions. Figure 7 shows the dependence of 3/2 11/2 3+ 0.471 with an increase in Nd O concentration. Therefore, it β /β on the spectroscopic quality factor χ for Nd 2 3 J (11/2) J (13/2) 4 4 is concluded that the efficiency for the F → I transition ions. The solid line in Figure 7 represents other laser materi- 3/2 9/2 4 4 increased and the efficiency for the F → I transition als. The tendencies of the β /β are absolutely con- 3/2 11/2 J (11/2) J (13/2) decreased as the difference of Ω ≥ Ω is bigger with increase sistent with that of quality factor shown in Figure 6. 4 6 Intensity (cm ) Quality factor (χ) Branching ratio (β) 6 Advances in OptoElectronics −20 ×10 6.5 3.5 2.5 5.5 1.5 4.5 0.5 0.51 1.52 Spectroscopic quality factor (χ) 0.51 1.522.53 Nd O concentration (wt%) 2 3 Figure 7: Dependence of β /β on the spectroscopic qual- J (11/2) J (13/2) 4 4 3+ F I 1059 nm 3/2 11/2 ity factor χ for Nd ions in the Bi(PO ) −Ba(PO ) −BaF −MgF 3 3 3 2 2 2 4 4 F I 1332 nm 3/2 13/2 glass system. Figure 8: Variation of emission cross section (σ ) as a function em of Nd O concentration in the Bi(PO ) −Ba(PO ) −BaF −MgF 2 3 3 3 3 2 2 2 4.3. Radiative lifetime and stimulated glass system. emission cross-section The radiative lifetimes (τ ) are related to the total radia- rad lifetime measured (W = 1/τ ) has the relations with the ra- tive transition probabilities A of all transitions from the M rad diative and nonradiative lifetimes as follows: initial J manifold to the final J manifold because the transi- tions from the individual excited state to the lowerlying man- W = W + W + W . (10) M R NR E ifolds should have the same measured lifetime because they all originate from the same excited state. It, therefore, in- 3+ W is the fluorescence decay rate determined by measuring volves the effective average over site-to-site variation of Nd 4 4 the lifetime of the F → I transition. In the experi- 3/2 11/2 ion environment in host materials. Because of the negligible 4 3+ ments, τ (= 1/W ) was measured as a function of the med M contribution of transition from I of Nd , the total ra- 15/2 3+ Nd ion concentration shown in Figure 3. W is the non- NR diative transition probabilities A for three transitions are rad 4 radiative decay rate due to multiphonon loss and W are an summed up to obtain the radiative lifetime τ from the F rad 3/2 additional nonradiative decay rate due to the energy transfer metastable state using 3+ processes between Nd . As shown in Figure 3, the fluores- 4 4 cence decay curves of the F → I transition at 0.5 wt% 3/2 11/2 τ (J ) = . (9) rad concentration shows a nonexponential behavior. But the flu- A(aJ , bJ ) orescence decay curves shows exponentially decay at high concentration. The lifetimes were determined by fitting the The values of the radiative lifetime at 1.5 wt% Nd O -doped 2 3 tail of the decay curve to a single exponential. For direct ex- sample are added to obtain the total radiative rates of 188, citation, radiative quantum efficiency (η = τ /τ )ofthe 4 4 4 med rad 1087, and 1189 for the I , I ,and I states, respec- 13/2 11/2 9/2 4 4 F → I transition is defined as the ratio between emit- 3/2 11/2 tively. Therefore, according to (5) the radiative lifetimes of ted light intensity and absorbed pump intensity. Note that ra- these levels are determined to be 5.31, 92.0, and 84.1 millisec- diative quantum efficiency monotonically decrease as a func- onds, respectively. Radiative lifetimes according to different tion of Nd O concentration listed in Table 3. 2 3 concentration of Nd O are given in Table 3. Figure 8 shows 2 3 the variation of stimulated emission cross-section as a func- 4.5. Multiphonon relaxation analysis tion of Nd O concentration. The stimulated cross-section 2 3 4 4 −20 for the F → I transition decreases from 3.51 × 10 3/2 11/2 −20 4 4 First of all, the nonradiative relaxation of excited states of to 1.7 × 10 and that for the F → I transition also 3/2 13/2 −21 −21 rare earth ions is through the emission of phonons, where decreases from 6.1 × 10 to 3.0 × 10 . we assume that nonradiative effects due to multiphonon re- 3+ laxation are negligible at low concentration of Nd ions. The 4.4. Fluorescence decay rate and quantum efficiency nonradiative rate contributed from multiphonon relaxation is given as follows: The relaxation from excited state is represented by both ra- diative and nonradiative modes. The total transition proba- W = C 1+ n(T ) exp(−α · ΔE), (11) mp bility, for example, the reciprocal of the fluorescence decay Ratio of intermanifold branching ratios (β /β ) J (11/2) J (13/2) Emission cross section (cm ) Ju H. Choi et al. 7 where C is a host dependent constant and p accounts for the effective number of phonons involved in the nonradia- tive process. ΔE is the energy gap between the F and 3/2 I levels. α is represented by a function of ω and the 4000 15/2 max electron-phonon coupling constant as follows: ln(ε) α =− , (12) max where ε is the ratio of the multiphonon relaxation rate for a p-phonon process W to that for (p − 1) phonon pro- cess W [28]. Since the rate of multiphonon relaxation at a p−1 temperature T is influenced by the population of the phonon −1 mode, n(T ) = [exp(ω/kT ) − 1] , it is described by Bose- 0 5 10 15 20 25 Einstein relation 40 2 2 Ion concentration (×10 ions /cm ) exp(ω/kT ) W (T ) = W , (13) mp 0 exp(ω/kT ) − 1 Figure 9: Quadratic relation between Nd O concentration and the 2 3 non-radiative decay rate. where W is obtained at T = 0K and (9). It can be reduced as follows: The theoretical expression for the dipole-dipole interac- W = W exp(−αΔE). (14) mp 0 tions is as follows: In this experiment, W was obtained using the measured life- 0 3/s t 4 t times at 20 K. Φ(t) = Φ(0) exp − − πΓ(1/2)N R , (15) τ 3 τ In order to calculate the quantitative contribution from multiphonon relaxation to the nonradiative relaxation, IR where N is the acceptor concentration, Γ is the Euler func- transmittance spectra were analyzed. The phonon energy, tion, s is a number which equals 6, and R is a critical ra- ω, estimated from strong side band is found to be about dius corresponding to the equality between the nonradia- −1 4 3+ 1126 cm in this system. The energy gap, ΔE,between F 3/2 tive intrinsic Nd relaxation and the transfer rates. The val- 4 −1 and I levels is found to be about 5656 cm .The num- ues of τ and R obtained from this simulation are, respec- 15/2 0 ber of phonon mode and the value of ε are found to be 5.02 tively, almost equal to 178 μsand 8.4 A. The latter parameter 3+ and 0.008, respectively. α calculated using (10)isfound to be is larger than the mean distance (R = 7.3 A) between Nd −3 1/3 4.28×10 cm. Using above parameters, the multiphonon re- ions (R = (3/4πN ) ) which means that energy transfer is −1 20 −3 laxation rate, W , was calculated to be about 73 s . There- mp very possible for concentration higher than 4.3 × 10 cm . fore, the multiphonon relaxation until 1 wt% Nd O doped 2 3 system is reasonably described with a so-called energy gap 5. CONCLUSION REMARKS law assuming the energy transfer is not predominant. 3+ The systematic spectroscopic analysis of Nd in Bi(PO ) – 3 3 Ba(PO ) −BaF −MgF systems has been performed using 3 2 2 2 4.6. Energy transfer analysis using Dexter model Judd-Ofelt theory. It has been found that the intensity pa- 3+ −20 On the other hand, the possible explanation for the de- rameter Ω for Nd slightly decreases from 2.54 × 10 4 4 −20 2 crease of fluorescence lifetime of the F → I transi- to 1.12 × 10 (pm ) with increase in Nd O concentra- 3/2 11/2 2 3 3+ 3+ tion can be explained by the energy transfer among Nd tion. The intensity parameters Ω ,and Ω for Nd have 4 6 −20 −20 ions when this concentration increases. Energy transfer from been found to decrease from 6.86 × 10 to 3.09 × 10 3+ 3+ −20 −20 2 Nd ion to another Nd ion may result from exchange in- and 5.74 × 10 to 2.87 × 10 (pm ), respectively, with teraction, radiation reabsorption, or multipole-multipole in- increasing in Nd O concentration from 0.5 wt% to 3 wt%. 2 3 4 4 teraction. Thus, W , for example, the additional nonradia- It has been found that the efficiency for the F → I E 3/2 9/2 4 4 tive decay rate must be considered. Nonradiative decay rate transition enhances and the efficiency for the F → I 3/2 11/2 3+ increases with an increase in Nd concentration and the transition diminishes as the difference between Ω and Ω 4 6 non-radiative decay rate presents a quadratic dependence on increases with increasing Nd O concentration. In addition, 2 3 3+ Nd concentration in current systems as shown in Figure 9, it has been observed that the emission cross-section for the 4 4 −21 this feature can be analyzed by using the Dexter model which F → I transition decrease from 6.1 × 10 to 3.0 × 3/2 13/2 −21 2 4 4 attributes the dominant energy transfer mechanism to the 10 (cm ) and those for the F → I transition de- 3/2 11/2 −20 −20 dipole-dipole interactions and proportional to the inverse of creases from 3.51× 10 to 1.7× 10 . The branching ratio 4 4 the sixth power of the distance separating the two ions and for the F → I transition will show the opposite trends 3/2 11/2 4 4 consequently to the squared concentration. According to the compared to the F → I transition. It slightly decreases 3/2 9/2 selection rules ΔJ = 0,±1, only the dipole-dipole interac- to 0.459 at 1 wt% and then increases to 0.471 with increase tions are allowed. in Nd O concentration. Therefore, it is concluded that the 2 3 −1 Non radiative lifetime ( s ) 8 Advances in OptoElectronics 4 4 efficiency for the F → I transition increased and the [17] G. S. Ofelt, “Intensities of crystal spectra of rare-earth ions,” 3/2 9/2 4 4 Journal of Chemical Physics, vol. 37, no. 3, pp. 511–520, 1962. efficiency for the F → I transition decrease as the dif- 3/2 11/2 [18] W. T. Carnall, J. P. Hessler, and F. W. Wagner, “Transition ference of Ω ≥ Ω is bigger with increase in Nd O con- 4 6 2 3 3+ 3+ probabilities in the absorption and fluorescence spectra of lan- centration. Energy transfer from Nd ion to another Nd thanides in molten lithium nitrate -potassium nitrate eutec- ion starts at more than 1 wt% Nd O which may result from 2 3 tic,” Journal of Physical Chemistry, vol. 82, no. 20, pp. 2152– exchange interaction, radiation reabsorption, or multipole- 2158, 1978. multipole interaction. [19] M. J. F. Digonnet, Rare Earth Doped Fiber and Amplifiers,Mar- cel Dekker, New York, NY, USA, 1993. [20] G. A. Kumar, A. Martinez, and E. De La Rosa, “Stimulated REFERENCES 3+ emission and radiative properties of Nd ions in barium flu- [1] E. Pecoraro, J. A. Sampaio, L. A. O. Nunes, S. Gama, and orophosphate glass containing sulphate,” Journal of Lumines- cence, vol. 99, no. 2, pp. 141–148, 2002. M. L. Baesso, “Spectroscopic properties of water free Nd O - 2 3 [21] R. C. Powell, Physics of Solid-State Laser Materials, Springer, doped low silica calcium aluminosilicate glasses,” Journal of Non-Crystalline Solids, vol. 277, no. 2-3, pp. 73–81, 2000. New York, NY, USA, 1998. 3+ [22] H. Ebendorff-Heidepriem, D. Ehrt, M. Bettinelli, and A. [2] M. Naftaly and A. Jha, “Nd -doped fluoroaluminate glasses for a 1.3 μm amplifier,” Journal of Applied Physics, vol. 87, no. 5, Speghini, “Effect of glass composition on Judd-Ofelt parame- 3+ ters and radiative decay rates of Er in fluoride phosphate and pp. 2098–2104, 2000. [3] E. Snitzer, “Optical maser action of Nd in a barium crown phosphate glasses,” Journal of Non-Crystalline Solids, vol. 240, no. 1–3, pp. 66–78, 1998. glass,” Physical Review Letters, vol. 7, no. 12, pp. 444–446, 1961. [4] S. V. J. Lkshmn and Y. C. Rantnkaran, “Electronic-spectra of [23] C. K. Jørgensen and R. Reisfeld, “Judd-Ofelt parameters and chemical bonding,” Journal of the Less Common Metals, vol. 93, the triply ionized neodymium ion in certain sulfate glasses,” Physics and Chemistry of Glasses, vol. 29, p. 26, 1988. no. 1, pp. 107–112, 1983. [24] R. D. Peacock, “The intensities of lanthanide f → f transi- [5] B. Viana, M. Palazzi, and O. LeFol, “Optical characterization 3+ of Nd doped sulphide glasses,” Journal of Non-Crystalline tions,” Structure and Bonding, vol. 22, pp. 83–122, 1975. 4 4 Solids, vol. 215, no. 1, pp. 96–102, 1997. [25] R. R. Jacobs and M. J. Weber, “Dependence of the F → I 3/2 11/2 3+ 3+ induced-emission cross section for Nd on glass composi- [6] S.Jiang,T.Luo,B.C.Hwang,etal., “Er -doped phosphate glasses for fiber amplifiers with high gain per unit length,” tion,” IEEE Journal of Quantum Electronics,vol. 12, no.2,part 1, pp. 102–111, 1976. Journal of Non-Crystalline Solids, vol. 263-264, pp. 364–368, 2000. [26] M. Ajroud, M. Haouari, H. Ben Ouada, H. Maaref, A. Brenier, and C. Garapon, “Investigation of the spectroscopic proper- [7] D. Ehrt, “Structure and properties of fluoride phosphate 3+ glasses,” in Damage to Space Optics, and Properties and Char- ties of Nd -doped phosphate glasses,” Journal of Physics: Con- densed Matter, vol. 12, no. 13, pp. 3181–3193, 2000. acteristics of Optical Glass, vol. 1761 of Proceedings of SPIE,pp. 213–222, San Diego, Calif, USA, July 1992. [27] E. De La Rosa,G.A.Kumar,L.A.Diaz-Torres,A.Mart´ ınez, and O. Barbosa-Garc´ ıa, “Spectroscopic characterization of [8] D. Kopf, F. X. Kar ¨ tner, U. Keller, and K. J. Weingarten, “Diode- 3+ pumped mode-locked Nd: glass lasers with an antiresonant Nd ions in barium fluoroborophosphate glasses,” Optical Materials, vol. 18, no. 3, pp. 321–329, 2001. Fabry-Perot saturable absorber,” Optics Letters, vol. 20, no. 10, pp. 1169–1171, 1995. [28] C. B. Layne, W. H. Lowdermilk, and M. J. Weber, “Multi- [9] W. Vogel, Glass Chemistry, chapter 7, Springer, Berlin, Ger- phonon relaxation of rare-earth ions in oxide glasses,” Physical Review B, vol. 16, no. 1, pp. 10–20, 1977. many, 1992. [10] A. A. Margaryan, Ligands and Modifiers in Vitreous Materials, World Scientific, Singapore, 1999. [11] A. Margaryan, A. Margaryan, J. H. Choi, and F. G. Shi, “Spec- 2+ troscopic properties of Mn in new bismuth and lead con- tained fluorophosphate glasses,” Applied Physics B: Lasers and Optics, vol. 78, no. 3-4, pp. 409–413, 2004. [12] J. H. Choi, A. Margaryan, A. Margaryan, and F. G. Shi, “Spec- 3+ troscopic properties of Yb in heavy metal contained flu- orophosphate glasses,” Materials Research Bulletin, vol. 40, no. 12, pp. 2189–2197, 2005. [13] J. H. Choi, A. Margaryan, A. Margaryan, and F. G. Shi, “Judd- 3+ Ofelt analysis of spectroscopic properties of Nd -doped novel fluorophosphate glass,” Journal of Luminescence, vol. 114, no. 3-4, pp. 167–177, 2005. [14] J. H. Choi, A. Margaryan, A. Margaryan, and F. G. Shi, “Op- 3+ tical transition properties of Yb in new fluorophosphate glasses with high gain coefficient,” Journal of Alloys and Com- pounds, vol. 396, no. 1-2, pp. 79–85, 2005. [15] J. H. Choi, F. G. Shi, A. Margaryan, and A. Margaryan, “Re- fractive index and low dispersion properties of new fluo- rophosphate glasses highly doped with rare-earth ions,” Jour- nal of Materials Research, vol. 20, no. 1, pp. 264–270, 2005. [16] B. R. Judd, “Optical absorption intensities of rare-earth ions,” Physical Review, vol. 127, no. 3, pp. 750–761, 1962. 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