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Spectroscopic studies of preparation conditions role on the shielding properties of MoO3-doped Na2O–ZnO–P2O5

Spectroscopic studies of preparation conditions role on the shielding properties of MoO3-doped... Glassy samples from the undoped ternary system Na O–ZnO–P O in combination with other samples from the same system 2 2 5 doped with variable amounts of MoO (0.25, 0.5, or 1 gm/batch) were successfully melted under ordinary, oxidizing, or reducing conditions followed by annealing. Fourier transform infrared spectrophotometric measurements in combination with optical absorption spectra were recorded before and after doping with variable concentrations of MoO in multiple melting media both as prepared or after being subjected to (8 Mrad) gamma irradiation dose. The studied spectral properties of the glasses were correlated with variations with the existing valence state of the Mo ions and the effects of gamma irradiation on the optical spectra and IR vibrational bands together with the role of the condition of melting the batches. The optical 3+ spectra of the glasses reveal pronounced UV and visible bands due to trace iron (F e ) ions as impurities or the sharing of the 2 3 low valence states of the added molybdenum ions. The FTIR peaks show condensed spectra of phosphate groups (Q, Q ), and the effects of dopant are limited because of low percent. Gamma irradiation causes distinct variations in the undoped spectra, but the MoO -doped glasses show some shielding behavior. Keywords Phosphate glass · MoO  · Melting condition · Fourier transform infrared (FTIR) · Optical (UV/Vis) · Gamma irradiation Introduction beside variable optical and electrical properties [1–3]. The low chemical durability of phosphate glasses can be over- Phosphate glasses can be classified as one of the three come by the introduction of multi-valent oxides such as extensively studied vitreous glassy systems alongside tra- Al2O3, PbO, and Fe2O3 which extended the applications of ditional silicate and borate glasses. Phosphate glasses pos- phosphate glasses including metal-sealing, optical compo- sess extended chemical compositions, and all have the basic nents, to encapsulation of some types of radioactive wastes, building structural PO4 group. They can incorporate high and as biomaterials [4–6]. The incorporation of the specific contents of a transition metal or rare earth oxides with the transition metal oxides, MoO or WO displays special sci- 3 3 result of obtaining candidates with distinct brilliant colors entific interest besides the potential applications in various fields of optics [7 –9]. Molybdenum ions like tungsten ions can be introduced * Mohamed M. Ibrahim in glasses in four different possible oxidation states, namely mr.physics60@yahoo.com 3+ 3 4+ 2 5+ 1 6+ o Mo (d), Mo (d), Mo (d ), or Mo (d ) or a mixture Building Physics Institute, Housing & Building Research of some of these states [10–13]. Parke et al. [10–14] reported Center, Dokki, Cairo, Egypt 3+ the presence of Mo ions in phosphate glassy matrix show- Glass Research Department, National Research Centre, 33 ing absorption bands at nearly 360 and 460 nm in their opti- Elbehouth St, Dokki 12311, Giza, Egypt cal spectra in addition to other absorption bands within the Physics Department, Faculty of Science, Al-Azher spectral ranges 360–380 and 710–780 nm assigned to the University, Nasr City, Cairo, Egypt 5+ 4+ presence of Mo ions, while Mo ions showed an absorp- Spectroscopy Department, National Research Centre, 33 tion band at about 550 nm. It has been recognized that the Elbehouth St, Dokki 12311, Giza, Egypt presence of a high level of MoO or WO produces a photo- 3 3 Basic Science Department, International Coastal Road, chromic effect [15– 17]. Structural studies of these specific Horus University, New Damietta, Damietta, Egypt Vol.:(0123456789) 1 3 Journal of the Australian Ceramic Society glasses indicated the formation of WO clusters and these at a temperature of 1100 ± 20 °C for 90 min with rotating highly polarizable clusters are responsible for the nonlinear the melts at intervals of 30 min to promote complete mixing and photochromic properties. However, glasses containing and acceptable homogeneity. The melts were poured into such transition metal ions often exhibit an intense and broad warmed stainless steel molds with the required dimensions. absorption band in the visible and near-IR regions which The prepared samples were transferred immediately to an is attributed to the reduction of these transition metals to annealing muffle furnace regulated at 280 °C. After 1 h, the lower valencies during melting at high temperatures [7]. It is muffle was switched off and left to cool with the samples evident that redox effects during melting without controlled inside to room temperature at a rate of 30 °C /hour. procedure produce absorption bands that limit the applica- tion of such glasses containing MoO or WO as optical 3 3 candidates [9]. In this study, glasses were prepared based on the system Techniques or methods of measurements Na O–ZnO–P O with increasing added MoO as dopant of properties 2 2 5 3 oxide (0.25, 0.5, 1%) with variable conditions of melting including normal melting under the atmospheric condition Optical absorption measurements without any addition. Two other varieties of glasses were prepared through the addition of either oxidizing agent The optical (UV–visible) absorption spectra before and after (NaNO ) or of reducing agent (sugar). The study includes gamma irradiation were measured at room temperature in the investigation of optical and FT-infrared absorption spec- the range from 200 to 2500 nm using a recording spectro- tra of the collectively prepared glasses within the three con- photometer (type Shimadzu UV-3600, UV–VIS-NIR Spec- ditions of melting. The same spectral measurements were trophotometer, Japan). Polished samples of equal thickness repeated after subjecting the glasses to a gamma dose of 8 (2 mm ± 0.1 mm) were measured, before and after gamma Mrad (8 × 10  Gy). This specific dose of gamma irradiation irradiation. The samples were measured twice to confirm the has been selected because earlier studies by the sharing of accuracy of the absorption peaks. one of the authors showed that the intensities of generated defects in glasses increased with progressive increase in the dose of radiation until reaching about 6 Mrad,{18–20}. After that, a saturation of the induced defects was assumed Infrared absorption measurements to be reached. A further study in this work was carried out of measuring the thermal expansion properties of some The infrared absorption spectra of the glasses were measured −1 at room temperature in the range 4000–400  cm by (Nicolet selected glasses. These collective studies are expected to give more insight into the states of molybdenum ions on the 6700 FT-IR, USA) infrared spectrophotometer, using the KBr technique disc. Two milligrams of powdered samples three conditions of melting. Also, the work is intended to justify the effects of gamma irradiation on the two spectral was mixed with 200 mg of KBr, and the mixture was sub- jected to a load of 5 tons/cm to produce clear homogenous properties of the studied glasses. discs. The infrared absorption spectra were measured imme- diately at room temperature after preparing the desired discs −1 Experimental details to avoid moisture attack, with a resolution of 2  cm . At least two IR spectra for each sample were recorded. Infra- Preparation of the glasses red spectra were corrected for the dark current noises and background using the two-point baseline corrections. After Glasses from the system P O –Na O–ZnO with varying correction, the IR spectra were analyzed using the deconvo- 2 5 2 lution method to identify the various hidden or overlapped additions of MoO were prepared from chemically labo- ratory pure materials. They include sodium dihydrogen peaks. orthophosphate (NaH PO ) and ZnO. The chemicals used 2 4 are of a local company for the sodium dihydrogen phos- phate (ADWIC, Egypt, with 0.1% Fe as an impurity, while zinc oxide supplied by Sigma-Aldrich Co with Fe 0.001%., Irradiation facility molybdenum oxide (MoO ) from Alpha Chemika (India) with Fe 0.002% impurities. The dopant oxide MoO was An Indian Co gamma cell (2000 Ci) was used as a gamma- ray source with a dose rate of 1.5 Gy/s (150 rad/s) at a tem- added over the weight of batch as such with the percents (0.25, 0.5, 1%). The weighed batches were melted in covered perature of 30˚C. Each glass sample was subjected to a total dose of (8 Mrad = 8 × 10  Gy). porcelain crucibles in a SiC electric furnace (Vecstar, UK) 1 3 Journal of the Australian Ceramic Society The high content MoO (1%) shows a small distinct increase Results in both the UV and visible absorption with parallel behavior. X‑ray diffraction Optical (UV–Visible) absorption spectra Figure (1) illustrates the X-ray diffraction experimental data of the glasses melted under oxidizing of the studied glasses. XRD pattern reveals the absence of conditions (NaNO ) any sharp peaks indicating and confirming the amorphous nature of the prepared glasses. The optical spectra of the glasses melted under oxidizing conditions (added NaNO ) shown in Fig. (3) reveal very similar spectral absorption to that identified in the optical Optical absorption spectra shown in Fig. (2) of the glasses melted under normal conditions. Optical (UV–Visible) absorption spectra of the glasses melted under normal atmospheric conditions before and after gamma irradiation Optical absorption spectra of undoped and  MoO ‑doped glasses melted Figure (2) illustrates the optical spectrum of the undoped with reducing agent ternary phosphate (Na O–ZnO–P O ) glass before irradia- 2 2 5 tion which reveals strong UV absorption extending from Figure (4) illustrates the optical spectra of the studied glasses 200 to 345 nm and reveals four small peaks at about 320, melted in reducing conditions. The undoped glass of the 335, and 345 nm and without any distinct absorption up to basic composition Na O–ZnO–P O reveals strong ultravio- 2500 nm. 2 2 5 let absorption extending from 300 to about 400 nm with a The optical spectra of the three MoO -doped samples distinct peak at 345 nm and without any further absorption show similar behavior, revealing strong UV absorption with to the end of measurement at 2400 nm. The spectrum of the some shift extension to a higher wavelength than that for the glass containing the lowest MoO content (0.25%) reveals a undoped glass, with three peaks at 345 nm and succeeded strong UV absorption with a peak at 345 nm and followed by a broad visible band centered at 780–800 nm and with by a medium peak at 357 nm and succeeded by broadband two small curvature at 1890 and 2340 nm. The gamma-irra- extending from about 600 to 1100 nm with a broad peak diated undoped glass reveals a slight change of the absorb- centered at 812 nm. ance combined with the generation of an induced broad vis- The second MoO -doped glass (0.5%) shows a strong UV ible band centered at 580 nm. The irradiated MoO -doped absorption with a peak at 300 nm followed by two peaks at glasses reveal a slight decrease in the UV spectrum but 375 and 444 nm and succeeded by a broad visible–near-IR remain unchanged and parallel in the remaining spectrum. band centered at 815 nm. The third MoO -doped sample (1%) shows a spectrum consisting of a strong UV–near-vis- ible absorption from 200 to 500 nm with multi-split peaks at and followed by a centered visible peak at about 440 nm and succeeded by a strong visible–near IR broadband extending from about 530 nm to 1200 nm and with multi-split broad peaks at 716, 780, and 855 nm. FTIR spectra of the glasses melted under atmospheric and oxidizing conditions Figure (5) illustrates the IR spectral curves of the studied undoped and MoO -doped glasses melted at normal condi- tions. The IR spectrum of the undoped base glass reveals condensed vibrational bands within the mid-wave number −1 region 400–1500  cm followed by some separate peaks in the rest of the near IR spectrum. The detailed vibrational peaks identified from the undoped glass are summarized as Fig(1) X-ray diffraction of the studied samples follows: 1 3 Journal of the Australian Ceramic Society Fig(2) UV/Vis. optical absorption of prepared glasses of undoped sample and glasses containing variable Mo ion concentrations (0.25, 0.5, and 1%) melted under ordinary atmospheric conditions. (a) The appearance of a strong far-IR band with a peak at The IR spectra of the MoO -doped glasses reveal −1. 530  cm almost the same vibrational bands within the mid- -1 (b) A medium band is identified with two peaks at about region from 400 to 1500 cm as that observed from −1. 714 and 782  cm the undoped sample. Only some limited variations (c) A very broad band is identified extending from about are observed including the decrease in the intensities −1 900 to 1500  cm with their peaks at about 983, 1030, of the bands at about 1683, 2867, 2921, and 2438 −1 -1 1096, 1272, and 1460  cm . cm . (d) A separate band is observed with two peaks at about Figure (6) shows the IR spectra of the glasses melted −1 1648 and 1710  cm . under oxidizing conditions (addition of NaNO ). The (e) Four peaks are identified at about 2000, 2430, 2853, IR spectra of all the glasses are almost similar to the −1 and 2921  cm . spectrum identified from the undoped glasses melted (f) A broad near IR band extending from about 3000 to under normal atmospheric conditions. The only varia- −1 −1 3750  cm centered at 3438  cm . tion is that the intensities of the mid-bands from 850 to 1 3 Journal of the Australian Ceramic Society Fig(3) UV/Vis. optical absorption of prepared glasses of undoped sample and glasses containing variable MoO ion concentrations (0.25, 0.5, and 1%) melted under oxidizing conditions. -1 1500 cm in the highest MoO -doped glass are lower (b) A double split medium band with two peaks at 714 and −1 than that from the other samples.775  cm is observed. (c) A very broad and distinct band is identified extending from about 800 to 1500 -1 cm with multi-component four distinct peaks at -1 FT infrared absorption spectra of the studied 883, 960, 1096, 1272 cm and followed by a small -1 undoped and  MoO ‑doped glasses melted peak at about 1460 cm . −1 under reducing condition (d) A medium band is observed at 1648  cm . (e) Two connected split peaks are observed at 2857 and −1 Figure (7) illustrates the FTIR absorption spectra of the pre-2921  cm . −1 pared reduced glasses. The undoped glass shows the follow- (f) A very broad near IR band with a peak at 3438  cm . ing spectral features: The MoO -doped glasses show nearly the same funda- (a) A far- IR sharp peak is identified with a peak at mental vibrational bands in nearly their wave number posi- −1 530  cm . tions but reveal the high decrease in the intensities of the 1 3 Journal of the Australian Ceramic Society 2.5 2.5 0.25 MoO3 Base 2.0 2.0 1.5 1.5 1.0 1.0 After radiation 0.5 0.5 After radiation Before radiation Before radiation 0.0 0.0 50010001500 2000 2500 500 1000 1500 2000 2500 Wavelength (nm) Wavelength (nm) 2.5 2.5 After radiation 1 MoO3 0.50 MoO 2.0 2.0 1.5 1.5 1.0 1.0 0.5 0.5 Aftre radiation 0.0 0.0 500 1000 1500 2000 2500 5001000 1500 2000 2500 Wavelength (nm) Wavelength (nm) Fig(4) Optical absorption spectra of undoped and MoO -doped glasses melted under reducing conditions before and after gamma irradiation ( 8 M rad). −1 bands at 1648  cm and the rest of near IR peaks at 2857, FTIR Spectra after gamma irradiation −1 2921, 3438  cm . Figure (9) illustrates the FTIR of two selected glasses consist- ing of the base host glass and the highest MoO -doped sample Deconvoluted IR Spectra of the base host after gamma irradiation; the composition of the derived IR glass data with that obtained before irradiation indicates that gamma irradiation slightly reduces the intensities of the IR vibra- Figure (8) illustrates the deconvoluted IR spectrum of the tional bands in the undoped base glass. On the other hand, the base phosphate glass; the identified deconvoluted peaks are MoO -doped glass shows maintenance of the IR bands due to at: 490, 535, 706, 768, 867, 911, 1012, 1156, 1287, 1360, the shielding effect of molybdenum ions, and the IR spectrum -1 1455, 1645, and 1714 cm did not show any distinct variation after gamma irradiation. 1 3 Absorbance (a.u.) Absorbance (a.u.) Absorbance (a.u.) Absorbance (a.u.) 807 Journal of the Australian Ceramic Society 1.00 MoO 0.50 MoO 0.25 MoO Base 4000 3500 3000 2500 2000 1500 1000 500 -1 Wavenumber (cm ) Fig(5) FTIR absorption spectra of studied glassy samples melted Fig(7) FTIR absorption spectra of studied glassy samples melted under ordinary condition under reducing condition 345 nm. This specific strong UV absorption can be related 3+ to being due to absorption of trace iron (mainly F e ions) present as impurities within the chemicals used for the preparation of the host glass. This postulation is based primarily on the published review article on charge trans- fer spectra in glasses introduced by prof Duffy [18]. He classified different UV absorption generally identified in various undoped glasses and referred that some transition 3+ 6+ metal ions (e.g., F e, Cr ) produce high intense UV absorption even if present in the ppm-level. This type of absorption involves the transfer of an electron from the glass network to the metal ion, and normally, it is highly intense and nominated as a charge transfer type. The same assignment has been adopted by Ehrt et al. in their publi- cations [19, 20] and her recent review article [21]. ElBatal et al. [12, 22–25] have reconfirmed that the UV absorption bands identified in various phosphate glasses are corre- lated with trace ferric ions impurities within the chemicals used for their preparation. We accept the previous postula- tion regarding the origin of the UV absorption identified Fig(6) FTIR absorption spectra of studied glassy samples melted in the host undoped ternary phosphate glass to trace iron under oxidizing condition 3+ impurities ( Fe ions). Discussion Interpretation of the optical spectra of  MoO ‑doped glasses under varying Interpretation of the identified strong UV melting conditions. absorption in the optical spectrum of the undoped Na O–ZnO–P O glass. 2 2 5 Careful inspection of Figs.  2,  3 and 4 indicates that the optical spectra of MoO -doped glasses melted under ordi- Experimental optical results indicate the identification 3 nary conditions (Fig. 2) are very similar to those melted of distinct UV absorption with three peaks extending to 1 3 Absorbance 530 Journal of the Australian Ceramic Society 0.08 1.25 0.06 1.00 0.04 0.02 0.75 0.00 0.50 -0.02 -0.04 0.25 -0.06 0.00 -0.08 1800 1600 1400 1200 1000 800600 400 1800 1600 1400 1200 1000 800 600 400 -1 Wavenumber (cm ) -1 Wavenumber (cm ) Fig(8) Deconvoluted IR Spectrum of base Fig(9) FTIR for base host glass and the highest MoO -doped sample after gamma irradiation under oxidizing conditions (Fig. 3) and quite different than appearance of the curvatures at 840 nm refers to the pres- the optical spectra of glasses melted under reducing condi- ence of some pentavalent molybdenum ions. tion (Fig. 4). It is concluded that Figs. 2 and 3 indicate the presence The first two Figs.  2 and 3 have common and similar of both hexavalent molybdenum ions as major percent and UV–visible spectra consisting of extended UV spectra than secondary percent to the pentavalent molybdenum ions. that identified for the undoped glass beside the appear - The optical spectra are shown in Fig. (4) in comparison ance of three broad curvatures centered at 840, 1840, and with those shown in Figs. 2 and 3 indicate the appearance of 2320 nm. The mentioned spectral features identified in a high intense broad visible band centered at about 785 nm Figs. 2 and 3 refer to the presence of both hexavalent and beside the subsidiary UV band at about 370 nm. These dif- pentavalent molybdenum ions. The extension of the UV ferent spectral features refer to the dominance of the penta- absorption than that for the undoped glass indicates that valent molybdenum ions when glasses were melted under the hexavalent molybdenum ions with the (d ) configu- reducing conditions. ration exhibit an extra UV band. On the other hand, the The same introduced postulation and interpretations of the 6+ bands due to hexavalent Mo ions in the UV region and the 1 3 Normalized Absorbance Residuals Journal of the Australian Ceramic Society 5+ −1 visible broadband due to pentavalent Mo ions have been viii- The near IR broad band centered at about 3450  cm previously given by several authors [6–8, 15, 16, 20, 21]. can be related to vibrations of water, OH, POH. The observed limited changes between IR spec- Interpretation of the FT infrared spectra tra melted under different conditions are explained as of the studied glasses follows: The experimental FTIR spectra appear condensed within a- The distinct decrease in the intensities of the bands at −1 −1 the mid-region (400–1500  cm ), and the understanding and about 1640,2857,2921  cm and the near IR broadband −1 explanation of the detailed IR results are based on the fol- centered at 3439  cm upon increasing MoO (Fig. 4) lowing basis [24–30]. The formed IR vibrational bands are can be related to the chemical stability in the glasses 6+ virtually depending on the constitutional chemical compo- upon adding the TM ions (Mo ). This stability effect sition and specifically on the glass-forming oxide percent reduces the ability of the MoO -doped glasses to absorb which forms the fundamental building groups in the glass water or moisture in the powder form and thus the cited network, and hence, it can be recognized that: bands are known to be assigned to vibrations of water, OH, or POH. The previous results are concerned with a- The host glass is composed of main P O with 70% as a glasses melted under the ordinary atmospheric condition 2 5 network forming oxide with phosphate groups (mainly where the molybdenum ions are expected to be existing 2 3 Q and Q types) and with modifier oxide Na O with in both hexavalent and pentavalent states. 24%, and the rest is ZnO with 6%. ZnO is known to be b- The glasses melted under oxidizing conditions (Fig. 5) conditional oxide which can act as modifier oxide or for - reveal only the decrease in the mid-bands extending −1 mer with ZnO with the necessary oxygen ions available from about 900 -1350  cm where molybdenum ion from neighboring alkali oxide. concentration reaches (1% MoO ). These results can be b- The identified IR vibrational bands are representing fin- related to the suggested depolymerization effect caused gerprints of the network structural units in agreement to by the Mo ions through changing of the metaphosphate similar units in crystalline analogs. groups. Similar behavior has been identified by some c- Figs. 4, 5, and 6 reveal the vibrational bands for the same authors about the action of copper ions [28] or iron ions glasses after varying conditions of melting. Inspection [29] on phosphate glasses. Also, the distinct appearance and comparison of the details vibrational bands in the of the far-IR bands may be related to the addition of three figures indicate the resemblance of Figs.  4 and 5 NaNO which seems to affect the ability of the powder and show limited differences especially in the intensities grains to absorb water or moisture. of the bands. d- The assignments of the vibrational bands shown for Figure  (7) shows that the melting of the glasses the undoped glass in Figs.  5, 6 and the deconvoluted under reducing conditions causes the distinct decrease spectrum shown in Fig. (8) are summarized as follows in the main IR vibrational bands within the mid-region −1 [25–31]. 600–1350  cm . It can be suggested that during the melt- −1 i- The distinct broad far-IR band with a peak at 503  cm ing process with the reducing agent, the redox reaction can be related to bending vibrations of O–P–O bonding, between the molybdenum ions and the reducing agent (PO ) modes of metaphosphate groups. affects to some extent the structural building units lead- −1 ii- The peaks at about 704 and 780  cm are related to sym- ing to the decrease in their intensities. metric stretching vibrations of P-O-P linkages. iii- The peaks at 875 is correlated to asymmetric stretch of −1 P-O-P, while the IR bands at 1030 and 1097  cm are Interpretation of the effect of gamma due to symmetric and asymmetric stretching vibrations irradiation on the combined spectral of PO units, respectively. properties −1 iv- The peak at about 1276  cm is related to PO asym- metric stretching of the doubly bonded (P = O) modes. Eec ff t of gamma irradiation on glass −1 v- The peak at about 1626  cm is related to vibrations of OH, water. Perfect crystalline materials are realized to be unaffected vi- The band at about 2430 attributed for the residual carbon upon being subjected to ionizing gamma irradiation. On dioxide the other hand, glasses are accepted to be non-periodic −1 vii- The peaks at about 2867 and 2921  cm can be related solids and exhibit intrinsic defects or pre-existing defects to vibrations of water, OH. such as non-bridging oxygen, vacancies, and impurities, 1 3 Journal of the Australian Ceramic Society and upon gamma irradiation, some physical and chemical generated pairs of electrons and positive holes. The identi- properties are assumed to show changes. These formed- fied optical results of the MoO -doped glasses reveal that induced changes or defects can be followed by many tools molybdenum ions capture positive holes or shield their such as measuring their optical or E.S.R spectra after effects in increasing the UV absorption or the formation gamma irradiation. During gamma irradiation, pairs of of an induced visible positive hole. It can be assumed that electrons and positive holes are generated and thus induced molybdenum ions shield or retard the effect of generated defects are expected to be formed including ionization, positive holes. Several authors have agreed that molybde- radiolysis, and photochemical reactions [14, 20, 32]. num ions (and tungsten ions) are possessing the capability of reducing the effect of gamma irradiation [10, 31, 32]. This specific behavior can be related to the relatively heavy mass of the Mo ions which retard or block the free passages of Interpretation of gamma irradiation electrons or position holes during the irradiation process and on the optical spectra and FTIR spectra also to photochemical reaction as discussed before. of the studied glasses. Regarding the almost maintenance of the FTIR results after gamma irradiation, it is assumed that previous studies [40 → 43] Gamma irradiation on the undoped glass causes a slight indicate that the structural building units generally remain unaf- increase in the UV absorption besides the generation of fected by irradiation except by the identification of some change an induced visible band centered at 580 nm appeared in in the band angles and/or band lengths leading to slight changes base sample. These specific responses can be interpreted in the intensities of some of the vibrational bands. as follows: (a) The host undoped glass is a ternary phosphate glass (70 Conclusion P O–15 Na O–ZnO15 mol%) and generally, phosphate 2 5 2 glasses are favoring the lower valencies of the transition Glasses from the system P O 70%–Na O 24%–ZnO 6% con- 2 5 2 metal ions [4, 6, 9, 16]. Hence, the trace unavoidable sisting of undoped and doped with varying MoO contents iron impurities present in the glass contains a measur- (0.25–0.50–1%) were prepared under three varying conditions 2+ able percent of ferrous (F e ) ions besides some few (normal–atmospheric–oxidizing–reducing). Characterization 3+ ferric (Fe ) ions. This assumption is confirmed by the of the prepared glasses includes collective optical and FT appearance of curvature centered at 1070 nm which is infrared absorption spectra before and after gamma radiation accepted to be the characteristic position for the absorp- with a specified dose (8 Mrad). The spectral results indicate tion due to ferrous ions [9]. Upon gamma irradiation, that the two melting conditions of the normal atmospheric some of the ferrous ions react or capture liberated posi- and oxidizing conditions produce similar optical spectra tive holes and the net result is the formation of addi- while the reducing condition initiates the low valence state of 3+ 2+ + tional ferric ions (Fe ) or (Fe ) and the result is the pentavalent molybdenum. FTIR spectra reveal distinct vibra- 2 3 observed increase in the intensity of the UV absorp- tional bands due to (Q , Q ) structural phosphate groups. The tion in the vicinity of the characteristic position of the molybdenum ions as dopants cause no distinct variations in absorption of the ferric ions (200–310 nm) [9]. the IR spectra due to their low percent to affect the structural (b) The generation of an induced visible band upon gamma phosphate glasses Gamma irradiation affects the spectrum irradiation of the undoped glass can be related to the of the undoped glass through photochemical reactions with formation of phosphorus oxygen hole center (POHC) trace impurities, and the generation of an induced POHC. through the assumption of the effect of generated hole The MoO -doped glasses reveals shielding behavior toward center on the phosphate network itself. The same assump- gamma irradiation and the spectral curves show stability. tion has been accepted by various authors [13, 14, 20]. The MoO -doped glasses reveal quite different responses Conflict of interest toward gamma irradiation. The UV absorption shows a slight decrease in intensity and the visible absorption remains All authors declared that there is no conflict of interest. unchanged with parallel behavior. The last-mentioned results can be explained by assuming that the liberated electrons and positive holes are faced with the MoO -doped glasses Funding Open access funding provided by The Science, Technology & by two different transition metal ions (traces of iron ions Innovation Funding Authority (STDF) in cooperation with The Egyp- and dopants of molybdenum ions) and it is obvious that a tian Knowledge Bank (EKB). competition of reactions between the two TM ions and the 1 3 Journal of the Australian Ceramic Society Open Access This article is licensed under a Creative Commons Attri- 17. Santagneli, S.H., de Araujo, C.C., Strojek, W., Eckert, H., Poirier, bution 4.0 International License, which permits use, sharing, adapta- G., Ribeiro, S.J., Messaddeq, Y.: Structural studies of NaPO − tion, distribution and reproduction in any medium or format, as long MoO glasses by solid-state nuclear magnetic resonance and as you give appropriate credit to the original author(s) and the source, Raman spectroscopy. J. Phys. Chem. B 111(34), 10109–10117 provide a link to the Creative Commons licence, and indicate if changes (2007) were made. The images or other third party material in this article are 18. Duffy, J.A.: Charge transfer spectra of metal ions in glass. Phys. included in the article's Creative Commons licence, unless indicated Chem. Glasses 38(6), 289–292 (1997) otherwise in a credit line to the material. If material is not included in 19. 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El-Batal, H.A., Azooz, M.A., Ezz-El-Din, F.M., El-Alaily, N.A.: conjunction with Photonics Meeting 2020" (ILATOSPM) 2020 Interaction of gamma rays with calcium aluminoborate glasses 22-23 October 2020, Malaysia, Johor containing holmium or erbium. J. Am. Ceram. Soc. 84(9), 2065– 2072 (2001) 1 3 Journal of the Australian Ceramic Society 37. Sigel, G.H., Ginther, R.J.: Effect of iron on ultraviolet absorption 41. Piao, F., Oldham, W.G., Haller, E.E.: The mechanism of radia- of high purity soda-Silica glass. Glass Technol. 9(3), 66 (1968) tion-induced compaction in vitreous silica. J. Non-Cryst. Solids 38. Cook, L., MADER, K. H.: Ultraviolet transmission characteris- 276(1–3), 61–71 (2000) tics of a fluorophosphate laser glass. J. Am. Ceram. Soc. 65(12), 42. Abdelghany, A.M., ElBatal, F.H., Azooz, M.A., Ouis, M.A., 597–601 (1982) ElBatal, H.A.: Optical and infrared absorption spectra of 3d tran- 39. Primak, W.: Mechanism for the radiation compaction of vitreous sition metal ions-doped sodium borophosphate glasses and effect silica. J. Appl. Phys. 43(6), 2745–2754 (1972) of gamma irradiation. Spectrochim. Acta Part A Mol. Biomol. 40. Hobbs, L.W., Sreeram, A.N., Jesurum, C.E., Berger, B.A.: Struc- Spectrosc. 98, 148–155 (2012) tural freedom, topological disorder, and the irradiation-induced amorphization of ceramic structures. Nucl. Instrum. Methods Publisher's Note Springer Nature remains neutral with regard to Phys. Res., Sect. B 116(1–4), 18–25 (1996) jurisdictional claims in published maps and institutional affiliations. 1 3 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Australian Ceramic Society Springer Journals

Spectroscopic studies of preparation conditions role on the shielding properties of MoO3-doped Na2O–ZnO–P2O5

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Abstract

Glassy samples from the undoped ternary system Na O–ZnO–P O in combination with other samples from the same system 2 2 5 doped with variable amounts of MoO (0.25, 0.5, or 1 gm/batch) were successfully melted under ordinary, oxidizing, or reducing conditions followed by annealing. Fourier transform infrared spectrophotometric measurements in combination with optical absorption spectra were recorded before and after doping with variable concentrations of MoO in multiple melting media both as prepared or after being subjected to (8 Mrad) gamma irradiation dose. The studied spectral properties of the glasses were correlated with variations with the existing valence state of the Mo ions and the effects of gamma irradiation on the optical spectra and IR vibrational bands together with the role of the condition of melting the batches. The optical 3+ spectra of the glasses reveal pronounced UV and visible bands due to trace iron (F e ) ions as impurities or the sharing of the 2 3 low valence states of the added molybdenum ions. The FTIR peaks show condensed spectra of phosphate groups (Q, Q ), and the effects of dopant are limited because of low percent. Gamma irradiation causes distinct variations in the undoped spectra, but the MoO -doped glasses show some shielding behavior. Keywords Phosphate glass · MoO  · Melting condition · Fourier transform infrared (FTIR) · Optical (UV/Vis) · Gamma irradiation Introduction beside variable optical and electrical properties [1–3]. The low chemical durability of phosphate glasses can be over- Phosphate glasses can be classified as one of the three come by the introduction of multi-valent oxides such as extensively studied vitreous glassy systems alongside tra- Al2O3, PbO, and Fe2O3 which extended the applications of ditional silicate and borate glasses. Phosphate glasses pos- phosphate glasses including metal-sealing, optical compo- sess extended chemical compositions, and all have the basic nents, to encapsulation of some types of radioactive wastes, building structural PO4 group. They can incorporate high and as biomaterials [4–6]. The incorporation of the specific contents of a transition metal or rare earth oxides with the transition metal oxides, MoO or WO displays special sci- 3 3 result of obtaining candidates with distinct brilliant colors entific interest besides the potential applications in various fields of optics [7 –9]. Molybdenum ions like tungsten ions can be introduced * Mohamed M. Ibrahim in glasses in four different possible oxidation states, namely mr.physics60@yahoo.com 3+ 3 4+ 2 5+ 1 6+ o Mo (d), Mo (d), Mo (d ), or Mo (d ) or a mixture Building Physics Institute, Housing & Building Research of some of these states [10–13]. Parke et al. [10–14] reported Center, Dokki, Cairo, Egypt 3+ the presence of Mo ions in phosphate glassy matrix show- Glass Research Department, National Research Centre, 33 ing absorption bands at nearly 360 and 460 nm in their opti- Elbehouth St, Dokki 12311, Giza, Egypt cal spectra in addition to other absorption bands within the Physics Department, Faculty of Science, Al-Azher spectral ranges 360–380 and 710–780 nm assigned to the University, Nasr City, Cairo, Egypt 5+ 4+ presence of Mo ions, while Mo ions showed an absorp- Spectroscopy Department, National Research Centre, 33 tion band at about 550 nm. It has been recognized that the Elbehouth St, Dokki 12311, Giza, Egypt presence of a high level of MoO or WO produces a photo- 3 3 Basic Science Department, International Coastal Road, chromic effect [15– 17]. Structural studies of these specific Horus University, New Damietta, Damietta, Egypt Vol.:(0123456789) 1 3 Journal of the Australian Ceramic Society glasses indicated the formation of WO clusters and these at a temperature of 1100 ± 20 °C for 90 min with rotating highly polarizable clusters are responsible for the nonlinear the melts at intervals of 30 min to promote complete mixing and photochromic properties. However, glasses containing and acceptable homogeneity. The melts were poured into such transition metal ions often exhibit an intense and broad warmed stainless steel molds with the required dimensions. absorption band in the visible and near-IR regions which The prepared samples were transferred immediately to an is attributed to the reduction of these transition metals to annealing muffle furnace regulated at 280 °C. After 1 h, the lower valencies during melting at high temperatures [7]. It is muffle was switched off and left to cool with the samples evident that redox effects during melting without controlled inside to room temperature at a rate of 30 °C /hour. procedure produce absorption bands that limit the applica- tion of such glasses containing MoO or WO as optical 3 3 candidates [9]. In this study, glasses were prepared based on the system Techniques or methods of measurements Na O–ZnO–P O with increasing added MoO as dopant of properties 2 2 5 3 oxide (0.25, 0.5, 1%) with variable conditions of melting including normal melting under the atmospheric condition Optical absorption measurements without any addition. Two other varieties of glasses were prepared through the addition of either oxidizing agent The optical (UV–visible) absorption spectra before and after (NaNO ) or of reducing agent (sugar). The study includes gamma irradiation were measured at room temperature in the investigation of optical and FT-infrared absorption spec- the range from 200 to 2500 nm using a recording spectro- tra of the collectively prepared glasses within the three con- photometer (type Shimadzu UV-3600, UV–VIS-NIR Spec- ditions of melting. The same spectral measurements were trophotometer, Japan). Polished samples of equal thickness repeated after subjecting the glasses to a gamma dose of 8 (2 mm ± 0.1 mm) were measured, before and after gamma Mrad (8 × 10  Gy). This specific dose of gamma irradiation irradiation. The samples were measured twice to confirm the has been selected because earlier studies by the sharing of accuracy of the absorption peaks. one of the authors showed that the intensities of generated defects in glasses increased with progressive increase in the dose of radiation until reaching about 6 Mrad,{18–20}. After that, a saturation of the induced defects was assumed Infrared absorption measurements to be reached. A further study in this work was carried out of measuring the thermal expansion properties of some The infrared absorption spectra of the glasses were measured −1 at room temperature in the range 4000–400  cm by (Nicolet selected glasses. These collective studies are expected to give more insight into the states of molybdenum ions on the 6700 FT-IR, USA) infrared spectrophotometer, using the KBr technique disc. Two milligrams of powdered samples three conditions of melting. Also, the work is intended to justify the effects of gamma irradiation on the two spectral was mixed with 200 mg of KBr, and the mixture was sub- jected to a load of 5 tons/cm to produce clear homogenous properties of the studied glasses. discs. The infrared absorption spectra were measured imme- diately at room temperature after preparing the desired discs −1 Experimental details to avoid moisture attack, with a resolution of 2  cm . At least two IR spectra for each sample were recorded. Infra- Preparation of the glasses red spectra were corrected for the dark current noises and background using the two-point baseline corrections. After Glasses from the system P O –Na O–ZnO with varying correction, the IR spectra were analyzed using the deconvo- 2 5 2 lution method to identify the various hidden or overlapped additions of MoO were prepared from chemically labo- ratory pure materials. They include sodium dihydrogen peaks. orthophosphate (NaH PO ) and ZnO. The chemicals used 2 4 are of a local company for the sodium dihydrogen phos- phate (ADWIC, Egypt, with 0.1% Fe as an impurity, while zinc oxide supplied by Sigma-Aldrich Co with Fe 0.001%., Irradiation facility molybdenum oxide (MoO ) from Alpha Chemika (India) with Fe 0.002% impurities. The dopant oxide MoO was An Indian Co gamma cell (2000 Ci) was used as a gamma- ray source with a dose rate of 1.5 Gy/s (150 rad/s) at a tem- added over the weight of batch as such with the percents (0.25, 0.5, 1%). The weighed batches were melted in covered perature of 30˚C. Each glass sample was subjected to a total dose of (8 Mrad = 8 × 10  Gy). porcelain crucibles in a SiC electric furnace (Vecstar, UK) 1 3 Journal of the Australian Ceramic Society The high content MoO (1%) shows a small distinct increase Results in both the UV and visible absorption with parallel behavior. X‑ray diffraction Optical (UV–Visible) absorption spectra Figure (1) illustrates the X-ray diffraction experimental data of the glasses melted under oxidizing of the studied glasses. XRD pattern reveals the absence of conditions (NaNO ) any sharp peaks indicating and confirming the amorphous nature of the prepared glasses. The optical spectra of the glasses melted under oxidizing conditions (added NaNO ) shown in Fig. (3) reveal very similar spectral absorption to that identified in the optical Optical absorption spectra shown in Fig. (2) of the glasses melted under normal conditions. Optical (UV–Visible) absorption spectra of the glasses melted under normal atmospheric conditions before and after gamma irradiation Optical absorption spectra of undoped and  MoO ‑doped glasses melted Figure (2) illustrates the optical spectrum of the undoped with reducing agent ternary phosphate (Na O–ZnO–P O ) glass before irradia- 2 2 5 tion which reveals strong UV absorption extending from Figure (4) illustrates the optical spectra of the studied glasses 200 to 345 nm and reveals four small peaks at about 320, melted in reducing conditions. The undoped glass of the 335, and 345 nm and without any distinct absorption up to basic composition Na O–ZnO–P O reveals strong ultravio- 2500 nm. 2 2 5 let absorption extending from 300 to about 400 nm with a The optical spectra of the three MoO -doped samples distinct peak at 345 nm and without any further absorption show similar behavior, revealing strong UV absorption with to the end of measurement at 2400 nm. The spectrum of the some shift extension to a higher wavelength than that for the glass containing the lowest MoO content (0.25%) reveals a undoped glass, with three peaks at 345 nm and succeeded strong UV absorption with a peak at 345 nm and followed by a broad visible band centered at 780–800 nm and with by a medium peak at 357 nm and succeeded by broadband two small curvature at 1890 and 2340 nm. The gamma-irra- extending from about 600 to 1100 nm with a broad peak diated undoped glass reveals a slight change of the absorb- centered at 812 nm. ance combined with the generation of an induced broad vis- The second MoO -doped glass (0.5%) shows a strong UV ible band centered at 580 nm. The irradiated MoO -doped absorption with a peak at 300 nm followed by two peaks at glasses reveal a slight decrease in the UV spectrum but 375 and 444 nm and succeeded by a broad visible–near-IR remain unchanged and parallel in the remaining spectrum. band centered at 815 nm. The third MoO -doped sample (1%) shows a spectrum consisting of a strong UV–near-vis- ible absorption from 200 to 500 nm with multi-split peaks at and followed by a centered visible peak at about 440 nm and succeeded by a strong visible–near IR broadband extending from about 530 nm to 1200 nm and with multi-split broad peaks at 716, 780, and 855 nm. FTIR spectra of the glasses melted under atmospheric and oxidizing conditions Figure (5) illustrates the IR spectral curves of the studied undoped and MoO -doped glasses melted at normal condi- tions. The IR spectrum of the undoped base glass reveals condensed vibrational bands within the mid-wave number −1 region 400–1500  cm followed by some separate peaks in the rest of the near IR spectrum. The detailed vibrational peaks identified from the undoped glass are summarized as Fig(1) X-ray diffraction of the studied samples follows: 1 3 Journal of the Australian Ceramic Society Fig(2) UV/Vis. optical absorption of prepared glasses of undoped sample and glasses containing variable Mo ion concentrations (0.25, 0.5, and 1%) melted under ordinary atmospheric conditions. (a) The appearance of a strong far-IR band with a peak at The IR spectra of the MoO -doped glasses reveal −1. 530  cm almost the same vibrational bands within the mid- -1 (b) A medium band is identified with two peaks at about region from 400 to 1500 cm as that observed from −1. 714 and 782  cm the undoped sample. Only some limited variations (c) A very broad band is identified extending from about are observed including the decrease in the intensities −1 900 to 1500  cm with their peaks at about 983, 1030, of the bands at about 1683, 2867, 2921, and 2438 −1 -1 1096, 1272, and 1460  cm . cm . (d) A separate band is observed with two peaks at about Figure (6) shows the IR spectra of the glasses melted −1 1648 and 1710  cm . under oxidizing conditions (addition of NaNO ). The (e) Four peaks are identified at about 2000, 2430, 2853, IR spectra of all the glasses are almost similar to the −1 and 2921  cm . spectrum identified from the undoped glasses melted (f) A broad near IR band extending from about 3000 to under normal atmospheric conditions. The only varia- −1 −1 3750  cm centered at 3438  cm . tion is that the intensities of the mid-bands from 850 to 1 3 Journal of the Australian Ceramic Society Fig(3) UV/Vis. optical absorption of prepared glasses of undoped sample and glasses containing variable MoO ion concentrations (0.25, 0.5, and 1%) melted under oxidizing conditions. -1 1500 cm in the highest MoO -doped glass are lower (b) A double split medium band with two peaks at 714 and −1 than that from the other samples.775  cm is observed. (c) A very broad and distinct band is identified extending from about 800 to 1500 -1 cm with multi-component four distinct peaks at -1 FT infrared absorption spectra of the studied 883, 960, 1096, 1272 cm and followed by a small -1 undoped and  MoO ‑doped glasses melted peak at about 1460 cm . −1 under reducing condition (d) A medium band is observed at 1648  cm . (e) Two connected split peaks are observed at 2857 and −1 Figure (7) illustrates the FTIR absorption spectra of the pre-2921  cm . −1 pared reduced glasses. The undoped glass shows the follow- (f) A very broad near IR band with a peak at 3438  cm . ing spectral features: The MoO -doped glasses show nearly the same funda- (a) A far- IR sharp peak is identified with a peak at mental vibrational bands in nearly their wave number posi- −1 530  cm . tions but reveal the high decrease in the intensities of the 1 3 Journal of the Australian Ceramic Society 2.5 2.5 0.25 MoO3 Base 2.0 2.0 1.5 1.5 1.0 1.0 After radiation 0.5 0.5 After radiation Before radiation Before radiation 0.0 0.0 50010001500 2000 2500 500 1000 1500 2000 2500 Wavelength (nm) Wavelength (nm) 2.5 2.5 After radiation 1 MoO3 0.50 MoO 2.0 2.0 1.5 1.5 1.0 1.0 0.5 0.5 Aftre radiation 0.0 0.0 500 1000 1500 2000 2500 5001000 1500 2000 2500 Wavelength (nm) Wavelength (nm) Fig(4) Optical absorption spectra of undoped and MoO -doped glasses melted under reducing conditions before and after gamma irradiation ( 8 M rad). −1 bands at 1648  cm and the rest of near IR peaks at 2857, FTIR Spectra after gamma irradiation −1 2921, 3438  cm . Figure (9) illustrates the FTIR of two selected glasses consist- ing of the base host glass and the highest MoO -doped sample Deconvoluted IR Spectra of the base host after gamma irradiation; the composition of the derived IR glass data with that obtained before irradiation indicates that gamma irradiation slightly reduces the intensities of the IR vibra- Figure (8) illustrates the deconvoluted IR spectrum of the tional bands in the undoped base glass. On the other hand, the base phosphate glass; the identified deconvoluted peaks are MoO -doped glass shows maintenance of the IR bands due to at: 490, 535, 706, 768, 867, 911, 1012, 1156, 1287, 1360, the shielding effect of molybdenum ions, and the IR spectrum -1 1455, 1645, and 1714 cm did not show any distinct variation after gamma irradiation. 1 3 Absorbance (a.u.) Absorbance (a.u.) Absorbance (a.u.) Absorbance (a.u.) 807 Journal of the Australian Ceramic Society 1.00 MoO 0.50 MoO 0.25 MoO Base 4000 3500 3000 2500 2000 1500 1000 500 -1 Wavenumber (cm ) Fig(5) FTIR absorption spectra of studied glassy samples melted Fig(7) FTIR absorption spectra of studied glassy samples melted under ordinary condition under reducing condition 345 nm. This specific strong UV absorption can be related 3+ to being due to absorption of trace iron (mainly F e ions) present as impurities within the chemicals used for the preparation of the host glass. This postulation is based primarily on the published review article on charge trans- fer spectra in glasses introduced by prof Duffy [18]. He classified different UV absorption generally identified in various undoped glasses and referred that some transition 3+ 6+ metal ions (e.g., F e, Cr ) produce high intense UV absorption even if present in the ppm-level. This type of absorption involves the transfer of an electron from the glass network to the metal ion, and normally, it is highly intense and nominated as a charge transfer type. The same assignment has been adopted by Ehrt et al. in their publi- cations [19, 20] and her recent review article [21]. ElBatal et al. [12, 22–25] have reconfirmed that the UV absorption bands identified in various phosphate glasses are corre- lated with trace ferric ions impurities within the chemicals used for their preparation. We accept the previous postula- tion regarding the origin of the UV absorption identified Fig(6) FTIR absorption spectra of studied glassy samples melted in the host undoped ternary phosphate glass to trace iron under oxidizing condition 3+ impurities ( Fe ions). Discussion Interpretation of the optical spectra of  MoO ‑doped glasses under varying Interpretation of the identified strong UV melting conditions. absorption in the optical spectrum of the undoped Na O–ZnO–P O glass. 2 2 5 Careful inspection of Figs.  2,  3 and 4 indicates that the optical spectra of MoO -doped glasses melted under ordi- Experimental optical results indicate the identification 3 nary conditions (Fig. 2) are very similar to those melted of distinct UV absorption with three peaks extending to 1 3 Absorbance 530 Journal of the Australian Ceramic Society 0.08 1.25 0.06 1.00 0.04 0.02 0.75 0.00 0.50 -0.02 -0.04 0.25 -0.06 0.00 -0.08 1800 1600 1400 1200 1000 800600 400 1800 1600 1400 1200 1000 800 600 400 -1 Wavenumber (cm ) -1 Wavenumber (cm ) Fig(8) Deconvoluted IR Spectrum of base Fig(9) FTIR for base host glass and the highest MoO -doped sample after gamma irradiation under oxidizing conditions (Fig. 3) and quite different than appearance of the curvatures at 840 nm refers to the pres- the optical spectra of glasses melted under reducing condi- ence of some pentavalent molybdenum ions. tion (Fig. 4). It is concluded that Figs. 2 and 3 indicate the presence The first two Figs.  2 and 3 have common and similar of both hexavalent molybdenum ions as major percent and UV–visible spectra consisting of extended UV spectra than secondary percent to the pentavalent molybdenum ions. that identified for the undoped glass beside the appear - The optical spectra are shown in Fig. (4) in comparison ance of three broad curvatures centered at 840, 1840, and with those shown in Figs. 2 and 3 indicate the appearance of 2320 nm. The mentioned spectral features identified in a high intense broad visible band centered at about 785 nm Figs. 2 and 3 refer to the presence of both hexavalent and beside the subsidiary UV band at about 370 nm. These dif- pentavalent molybdenum ions. The extension of the UV ferent spectral features refer to the dominance of the penta- absorption than that for the undoped glass indicates that valent molybdenum ions when glasses were melted under the hexavalent molybdenum ions with the (d ) configu- reducing conditions. ration exhibit an extra UV band. On the other hand, the The same introduced postulation and interpretations of the 6+ bands due to hexavalent Mo ions in the UV region and the 1 3 Normalized Absorbance Residuals Journal of the Australian Ceramic Society 5+ −1 visible broadband due to pentavalent Mo ions have been viii- The near IR broad band centered at about 3450  cm previously given by several authors [6–8, 15, 16, 20, 21]. can be related to vibrations of water, OH, POH. The observed limited changes between IR spec- Interpretation of the FT infrared spectra tra melted under different conditions are explained as of the studied glasses follows: The experimental FTIR spectra appear condensed within a- The distinct decrease in the intensities of the bands at −1 −1 the mid-region (400–1500  cm ), and the understanding and about 1640,2857,2921  cm and the near IR broadband −1 explanation of the detailed IR results are based on the fol- centered at 3439  cm upon increasing MoO (Fig. 4) lowing basis [24–30]. The formed IR vibrational bands are can be related to the chemical stability in the glasses 6+ virtually depending on the constitutional chemical compo- upon adding the TM ions (Mo ). This stability effect sition and specifically on the glass-forming oxide percent reduces the ability of the MoO -doped glasses to absorb which forms the fundamental building groups in the glass water or moisture in the powder form and thus the cited network, and hence, it can be recognized that: bands are known to be assigned to vibrations of water, OH, or POH. The previous results are concerned with a- The host glass is composed of main P O with 70% as a glasses melted under the ordinary atmospheric condition 2 5 network forming oxide with phosphate groups (mainly where the molybdenum ions are expected to be existing 2 3 Q and Q types) and with modifier oxide Na O with in both hexavalent and pentavalent states. 24%, and the rest is ZnO with 6%. ZnO is known to be b- The glasses melted under oxidizing conditions (Fig. 5) conditional oxide which can act as modifier oxide or for - reveal only the decrease in the mid-bands extending −1 mer with ZnO with the necessary oxygen ions available from about 900 -1350  cm where molybdenum ion from neighboring alkali oxide. concentration reaches (1% MoO ). These results can be b- The identified IR vibrational bands are representing fin- related to the suggested depolymerization effect caused gerprints of the network structural units in agreement to by the Mo ions through changing of the metaphosphate similar units in crystalline analogs. groups. Similar behavior has been identified by some c- Figs. 4, 5, and 6 reveal the vibrational bands for the same authors about the action of copper ions [28] or iron ions glasses after varying conditions of melting. Inspection [29] on phosphate glasses. Also, the distinct appearance and comparison of the details vibrational bands in the of the far-IR bands may be related to the addition of three figures indicate the resemblance of Figs.  4 and 5 NaNO which seems to affect the ability of the powder and show limited differences especially in the intensities grains to absorb water or moisture. of the bands. d- The assignments of the vibrational bands shown for Figure  (7) shows that the melting of the glasses the undoped glass in Figs.  5, 6 and the deconvoluted under reducing conditions causes the distinct decrease spectrum shown in Fig. (8) are summarized as follows in the main IR vibrational bands within the mid-region −1 [25–31]. 600–1350  cm . It can be suggested that during the melt- −1 i- The distinct broad far-IR band with a peak at 503  cm ing process with the reducing agent, the redox reaction can be related to bending vibrations of O–P–O bonding, between the molybdenum ions and the reducing agent (PO ) modes of metaphosphate groups. affects to some extent the structural building units lead- −1 ii- The peaks at about 704 and 780  cm are related to sym- ing to the decrease in their intensities. metric stretching vibrations of P-O-P linkages. iii- The peaks at 875 is correlated to asymmetric stretch of −1 P-O-P, while the IR bands at 1030 and 1097  cm are Interpretation of the effect of gamma due to symmetric and asymmetric stretching vibrations irradiation on the combined spectral of PO units, respectively. properties −1 iv- The peak at about 1276  cm is related to PO asym- metric stretching of the doubly bonded (P = O) modes. Eec ff t of gamma irradiation on glass −1 v- The peak at about 1626  cm is related to vibrations of OH, water. Perfect crystalline materials are realized to be unaffected vi- The band at about 2430 attributed for the residual carbon upon being subjected to ionizing gamma irradiation. On dioxide the other hand, glasses are accepted to be non-periodic −1 vii- The peaks at about 2867 and 2921  cm can be related solids and exhibit intrinsic defects or pre-existing defects to vibrations of water, OH. such as non-bridging oxygen, vacancies, and impurities, 1 3 Journal of the Australian Ceramic Society and upon gamma irradiation, some physical and chemical generated pairs of electrons and positive holes. The identi- properties are assumed to show changes. These formed- fied optical results of the MoO -doped glasses reveal that induced changes or defects can be followed by many tools molybdenum ions capture positive holes or shield their such as measuring their optical or E.S.R spectra after effects in increasing the UV absorption or the formation gamma irradiation. During gamma irradiation, pairs of of an induced visible positive hole. It can be assumed that electrons and positive holes are generated and thus induced molybdenum ions shield or retard the effect of generated defects are expected to be formed including ionization, positive holes. Several authors have agreed that molybde- radiolysis, and photochemical reactions [14, 20, 32]. num ions (and tungsten ions) are possessing the capability of reducing the effect of gamma irradiation [10, 31, 32]. This specific behavior can be related to the relatively heavy mass of the Mo ions which retard or block the free passages of Interpretation of gamma irradiation electrons or position holes during the irradiation process and on the optical spectra and FTIR spectra also to photochemical reaction as discussed before. of the studied glasses. Regarding the almost maintenance of the FTIR results after gamma irradiation, it is assumed that previous studies [40 → 43] Gamma irradiation on the undoped glass causes a slight indicate that the structural building units generally remain unaf- increase in the UV absorption besides the generation of fected by irradiation except by the identification of some change an induced visible band centered at 580 nm appeared in in the band angles and/or band lengths leading to slight changes base sample. These specific responses can be interpreted in the intensities of some of the vibrational bands. as follows: (a) The host undoped glass is a ternary phosphate glass (70 Conclusion P O–15 Na O–ZnO15 mol%) and generally, phosphate 2 5 2 glasses are favoring the lower valencies of the transition Glasses from the system P O 70%–Na O 24%–ZnO 6% con- 2 5 2 metal ions [4, 6, 9, 16]. Hence, the trace unavoidable sisting of undoped and doped with varying MoO contents iron impurities present in the glass contains a measur- (0.25–0.50–1%) were prepared under three varying conditions 2+ able percent of ferrous (F e ) ions besides some few (normal–atmospheric–oxidizing–reducing). Characterization 3+ ferric (Fe ) ions. This assumption is confirmed by the of the prepared glasses includes collective optical and FT appearance of curvature centered at 1070 nm which is infrared absorption spectra before and after gamma radiation accepted to be the characteristic position for the absorp- with a specified dose (8 Mrad). The spectral results indicate tion due to ferrous ions [9]. Upon gamma irradiation, that the two melting conditions of the normal atmospheric some of the ferrous ions react or capture liberated posi- and oxidizing conditions produce similar optical spectra tive holes and the net result is the formation of addi- while the reducing condition initiates the low valence state of 3+ 2+ + tional ferric ions (Fe ) or (Fe ) and the result is the pentavalent molybdenum. FTIR spectra reveal distinct vibra- 2 3 observed increase in the intensity of the UV absorp- tional bands due to (Q , Q ) structural phosphate groups. The tion in the vicinity of the characteristic position of the molybdenum ions as dopants cause no distinct variations in absorption of the ferric ions (200–310 nm) [9]. the IR spectra due to their low percent to affect the structural (b) The generation of an induced visible band upon gamma phosphate glasses Gamma irradiation affects the spectrum irradiation of the undoped glass can be related to the of the undoped glass through photochemical reactions with formation of phosphorus oxygen hole center (POHC) trace impurities, and the generation of an induced POHC. through the assumption of the effect of generated hole The MoO -doped glasses reveals shielding behavior toward center on the phosphate network itself. The same assump- gamma irradiation and the spectral curves show stability. tion has been accepted by various authors [13, 14, 20]. The MoO -doped glasses reveal quite different responses Conflict of interest toward gamma irradiation. The UV absorption shows a slight decrease in intensity and the visible absorption remains All authors declared that there is no conflict of interest. unchanged with parallel behavior. The last-mentioned results can be explained by assuming that the liberated electrons and positive holes are faced with the MoO -doped glasses Funding Open access funding provided by The Science, Technology & by two different transition metal ions (traces of iron ions Innovation Funding Authority (STDF) in cooperation with The Egyp- and dopants of molybdenum ions) and it is obvious that a tian Knowledge Bank (EKB). competition of reactions between the two TM ions and the 1 3 Journal of the Australian Ceramic Society Open Access This article is licensed under a Creative Commons Attri- 17. 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Journal

Journal of the Australian Ceramic SocietySpringer Journals

Published: Mar 21, 2022

Keywords: Phosphate glass; MoO3; Melting condition; Fourier transform infrared (FTIR); Optical (UV/Vis); Gamma irradiation

References