Spectroscopic studies of lithium phosphate, lead phosphate and zinc phosphate glasses containing TiO2: Effect of gamma irradiation

Accepted Manuscript Spectroscopic Studies of Lithium Phosphate, Lead phosphate and Zinc Phos‐ phate Glasses containing TiO2: Effect of Gamma Irradiation N.A. Ghoneim, A.M. Abdelghany, S.M. Abo-Naf, F.A. Moustafa, Kh.M. ElBadry PII: DOI: Reference:

S0022-2860(12)01075-7 http://dx.doi.org/10.1016/j.molstruc.2012.11.034 MOLSTR 19371

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Journal of Molecular Structure

Received Date: Revised Date: Accepted Date:

21 August 2012 13 October 2012 19 November 2012

Please cite this article as: N.A. Ghoneim, A.M. Abdelghany, S.M. Abo-Naf, F.A. Moustafa, Kh.M. ElBadry, Spectroscopic Studies of Lithium Phosphate, Lead phosphate and Zinc Phosphate Glasses containing TiO2: Effect of Gamma Irradiation, Journal of Molecular Structure (2012), doi: http://dx.doi.org/10.1016/j.molstruc.2012.11.034

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Spectroscopic Studies of Lithium Phosphate, Lead phosphate and Zinc Phosphate Glasses containing TiO2: Effect of Gamma Irradiation N.A. Ghoneim1, A.M. Abdelghany*2, S.M. Abo-Naf1, F.A. Moustafa1, Kh.M. ElBadry1 1

Glass Research Department, National Research Center, Dokki, 12311, Cairo, Egypt 2

Spectroscopy Department, National Research Center, Dokki, 12311, Cairo, Egypt

Abstract Pristine lithium phosphate, lead phosphate and zinc phosphate glasses and glasses of the

same compositions containing TiO2 (0.25⇾2.5%) were prepared. UV-visible and infrared

absorption spectra of the prepared samples were measured before and after gamma irradiation. Optical spectra of these prepared glasses reveal strong UV absorption bands which are attributed to the presence of trace iron impurities in lithium and zinc phosphate glasses while the broad UV bands in lead phosphate glasses were related to absorption of both trace iron impurities and divalent lead ions. The TiO2-containing glasses reveal an extra two visible bands at about 550-580 and 680-740 nm due to the transitions 2B2g→2B1g and 2B2g→2A1g of distorted octahedral Ti3+ ions. The effects of gamma irradiation reveal variations, extended in the UV-visible region in the lithium phosphate while with lead phosphate and zinc phosphate samples the variations are restricted to UV spectra. The response to gamma irradiation on optical absorption has been analyzed for both the sharing of all glass constituents including trace iron impurities. Lead and zinc phosphate glaes reveal only induced UV bands from photochemical effect of trace iron impurities while lithium phosphate shows extra induced visible band due to positive holes. The effects of gamma irradiation on the IR spectra are limited to a slight decrease of the intensities for some IR bands. The IR spectra are observed to be slightly affected by the increase of TiO2 indicating the stability of the main phosphate network units and the shielding behavior of titanium ions.

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Keywords; Phosphate glasses; Optical & Infrared spectroscopy; Gamma irradiation; TiO2. Corresponding author E-mail : [email protected]

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: +2 0121133152

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1. Introduction Phosphate glasses doped with TiO2 have been studied in recent years for the possible technological applications associated mainly with their optical properties [1-3]. and also for the use as glass seals and low melting glass solders [4] and in biomedical applications [5, 6]. The chemical durability and other physical properties of phosphate glasses are improved by adding multivalent oxides such as Al2O3, PbO, MoO3, WO3, TiO2 etc. which extends their applications [7-10] even in the burial of radioactive wastes. Optical absorption studies on TiO2 –containing glasses [7, 11] indicate that under ordinary conditions of melting, titanium ions are incorporated into silicate glasses in its higher valence state as Ti4+ ions because it is difficult to obtain Ti3+ ions under such conditions. In alkali borate glasses, titanium ions are known to behave in a similar behavior as with silicate glasses. The Ti4+ state has the electronic configuration 3d0 which produces no absorption in the visible region but exhibits an ultraviolet band. In soda lime phosphate and sodium metaphosphate glasses, titanium ions exhibit a purple color due to the presence of Ti3+ ions in a measurable percent [3, 12]. The optical spectra of such glasses exhibit two characteristic visible bands at about 540 and 680 nm. These visible bands are attributed to the transitions 2B2g→2B1g and 2B2g→2A1g respectively [3, 11-13]. Gamma irradiation on most glasses has been shown to give rise to radiation defects which are generally characterized by induced optical absorption bands [14, 15]. The 3

induced defects generated by gamma irradiation originate from intrinsic defects within the glass matrix itself such as nonbridging oxygens produces positive hole centers and from the sharing of extrinsic defects due to dopants or impurities which may involve some photochemical release or absorption of librated electrons [15-17]. On the other hand, some of the glasses containing heavy metal ions (such as Pb2+, Bi3+) or transition metal oxides (e.g. CuO, V2O5) show shielding behavior towards successive gamma irradiation [18-20]. The main objective of this work is to investigate optical spectra of titanium ions in three selected and different phosphate glasses, namely lithium metaphosphate, lead metaphosphate and zinc metaphosphate before and after gamma irradiation (8Mrad). A second aim of the work is to measure the FTIR spectra of the prepared undoped and TiO2 doped phosphate glasses both before and after being subjected to a gamma dose of 8 Mrad (= 8 × 104 Gy). An additional objective of the work includes the identification of induced optical spectra and to justify the shielding effects of glass forming constituents and TiO2 towards gamma irradiation and to compare the effect of lithium, zinc and lead on the measured combined spectra.

2. Experimental details The glasses studied were classified into three basic series of phosphate glasses, namely: lithium phosphate, lead phosphate and zinc phosphate as shown in (table 1). 0.5% Al2O3 was added to each of the prepared glasses to stabilize, improve chemical 4

durability and to avoid devitrification. The glasses were prepared from reagent grade chemicals including lithium carbonate Li2CO3, ammonium dihydrogen phosphate (NH4H2PO4), red lead oxide (Pb3O4), zinc oxide (ZnO) and titanium dioxide (TiO2). Weighed batches were melted in porcelain crucibles in an electric furnace regulated at 1000-1200 °C for 90 minutes under atmospheric conditions. The melts were rotated at fixed intervals to achieve homogeneity and bubble free melts. Homogenous melts were poured into stainless steel molds with the required dimensions. The prepared samples were immediately transferred to an annealing muffle furnace regulated at 250 °C for lead phosphate glasses and 400 °C for lithium and zinc phosphate glasses. The muffle after 1 hour was left to cool with the samples inside to room temperature at a rate of 30 °C/hour. The optical absorption spectra within the ultraviolet and visible regions for polished samples of equal thickness (2mm ± 0.1 mm) were obtained with a recording double beam spectrophotometer (JASCO Corp, V-570, Rel. 60, Japan). The same measurements were repeated for the samples after gamma irradiation in the range (2001000 nm). Fourier transform infrared absorption spectra of the glasses were obtained with FTIR spectrometer (type Mattson, 5000, USA). Powdered glass samples (2mg) were mixed with KBr powder (200 mg) and pressed with 5 tons/cm2 to form thin transparent

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disks. Infrared absorption spectra within the range 400-2500 cm-1 were recorded immediately after the preparation of the disks. A 60Co 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 temperature of 30 °C. The investigated samples were subjected to the same gamma dose every time. Using a Fricke dosimeter, the observed dose in water was utilized in terms of dose in glass. No cavity theory correction was made. Each sample was subjected to a total dose of 8 × 104 Gy (8 Mrad).

3. Results 3.1. Optical UV-visible spectra of the three undoped phosphate glass Fig. 1(a) illustrates the UV-visible absorption spectrum of the undoped lithium phosphate glass and analyzed normalized spectra of irradiated sample which reveals a strong and broad UV absorption band centered at about 235 nm with two connected minor peaks at about 220 and 250 nm and no visible bands could be observed. On subjecting this glass to a total final gamma dose of 8MR, the UV absorption increases with the resolution of a broad band centered at about 325 nm followed by a broad asymmetrical visible band centered at about 825 nm which increases with progressive irradiation. Fig. 1(b) reveals the UV–visible absorption spectrum of the undoped lead phosphate glass and analyzed normalized spectra of irradiated sample showing a strong 6

and broad ultraviolet absorption comprising two peaks at about 230 and 275 nm and followed by a small peak at about 340 nm but with no obvious visible band. On subjecting the parent undoped lead phosphate glass to a final total gamma dose of 8MR, the UV absorption is extended from 200 to about 350 nm and showing three small peaks at about 230, 250, 280 nm and with a slight curvature at about 340 nm and no visible bands are observed. In this lead glass the absorption curves are seen to be approximately parallel with progressive irradiation especially in the visible and near IR regions from 700 to 2500 nm. Fig. 1(c) shows the UV–visible spectrum of undoped zinc phosphate glass and analyzed normalized spectra of irradiated sample which revealing a prominent ultraviolet band centered at about 235 nm with two subsidiary closely related small kinks at about 225 and 250 nm and with no visible bands. On subjecting this glass to a final gamma dose of 8MR, the UV absorption is observed to extend from 200 to about 400 nm with three small peaks at about 230, 255 and 290 nm and with a shoulder at about 345 nm. The induced optical spectrum of this zinc phosphate glass reveals no visible bands. The spectral curves are observed to increase in intensity with progressive irradiation but in parallelism behavior.

3.2. Optical absorption spectra of TiO2-containing samples before gamma irradiation. 3.2.1 Absorption spectra of TiO2 containing lithium phosphate glasses before irradiation 7

Figure (2-a) shows optical absorption spectra of the TiO2-doped lithium phosphate glasses before gamma irradiation.

The optical spectrum of the glass containing

0.25% TiO2 exhibits a strong and broad ultraviolet band centered at about 235 nm and the visible portion reveals two broad bands centered at 580 and 740 nm. With the increase of TiO2 content to 0.5%, both the strong UV absorption band and the two broad visible bands increase in intensity. With further increase to 0,75 % TiO2, the UV absorption extends to 350 nm with the appearance of two extra peaks at about 310 and 340 nm and the first broad visible band at 580 nm becomes more intense than the second band at 740 nm. With introducing 2.5 % TiO2, the UV spectrum extends to 380 nm showing a further distinct peak at 380 nm and the visible spectrum reveals the highest increase in the first band which moves its center to about 550 nm and the second band transforms to a broad curvature centered at 720 nm. 3.2.2. Absorption spectra of TiO2 containing lead phosphate glasses before irradiation

Figure (2-c) shows optical absorption spectra of the TiO2-doped lead phosphate glasses before gamma irradiation. The spectrum of the glass containing 0.25% TiO2 reveals strong and broad UV absorption extending to about 400 nm showing a prominent peak at 240 nm and a secondary peak at 340 nm and the visible spectrum exhibits two broad bands centered at 580 and 730 nm. On increasing the TiO2 content 0.5%, the UV absorption retains its spectral feature but the second peak shifts to 330 nm and the visible spectrum shows parallelism to the previous 0.25% TiO2 sample but with slightly lower intensity. With glasses containing 0.5% up to 2.5% TiO2, the intensity of 8

the UV absorption progressively decreases with TiO2 content and the visible spectra exhibit parallelism. 3.2.3. Absorption spectra of TiO2 containing zinc phosphate glasses before irradiation

Figure (2-e) shows optical absorption spectra of the TiO2-doped zinc phosphate glasses before gamma irradiation. The whole spectrum of the zinc phosphate glass containing 0.25% TiO2 reveals strong UV absorption extending from 200 to about 300 nm without distinctive central peak and is followed by a visible spectrum with small curvature at about 560 nm. Increasing the concentration of TiO2 to 0.5 %, the UVvisible spectrum of the glass is highly identified consisting of strong ultraviolet absorption showing four peaks, an intense one at about 230 nm and three small peaks at about 275, 300 and 330 nm and are followed by two broad visible bands, the first is high intense centered at about 550 nm and the second is less intense and centered at about 740 nm. Increasing the TiO2 content to 0.75%, the UV spectrum attains the same characteristic as the 0.5% TiO2 sample but the two visible bands reveal increase in intensity for both bands. The last glass containing 2.5% TiO2 shows a spectrum with a slight shift of the UV absorption but retains the same peaks while the two visible bands are highly intensified.

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3.3. Optical absorption spectra of TiO2-containing samples after gamma irradiation. 3.3.1 Lithium phosphate glasses Figure (2.b) illustrates the optical spectra of TiO2-containing lithium phosphate glasses after gamma irradiation (8Mrad) and the results can be summarized as follows; i.

On subjecting the glass (LiPTi1) containing (0.25%) TiO2, to a gamma dose of 8 Mrad, the strong UV spectrum is extended from 200 to about 350 nm

accompanied with the resolution of two peaks at 250 and 310 nm and the visible spectrum reveals a curvature around 400 nm and ended by two small broad bands centered at about 570 and 740 nm. ii.

The glass (LiPTi2) shows after gamma irradiation (8Mrad), almost the same spectral features of the previous (LiPTi1) sample but with higher intensities of the absorption bands of both UV and visible regions.

iii.

The third (LiPTi3) sample with (0.75 wt%) added TiO2, reveals after irradiation similar spectral features as LiPTi2 but with higher intensities for the two visible broad bands and their centers are shifted to 560 and 720 nm.

iv.

The last (LiPTi4) sample with (2.5 wt%) added TiO2, shows after irradiation the extension of the UV spectrum to resolve a third peak at about 380 nm and the two broad visible bands exhibit higher intensities 10

with shifting especially the first one reaching 550 nm and the second 700 nm. 3.3.2 Lead phosphate glasses Figure (2.d) reveals the UV-visible spectra of the TiO2-containing lead phosphate glasses after gamma irradiation (8Mrad) and the spectral features are summarized as follows; i.

The glass PbPTi1 containing (0.25 % TiO2) shows after irradiation nearly the same spectral characteristics as before irradiation exhibiting strong UV absorption bands with two peaks at about 250 and 340 nm and with two broad visible bands centered at 560 and 740 nm.

ii.

The samples PbPTi2, PbPTi3, PbPTi4 show obvious decrease of the overall intensities of the UV-vis. spectra upon gamma irradiation. This distinct behavior is observed specifically with phosphate glasses containing high PbO content.

3.3.3 Zinc phosphate glasses Figure (2.f) illustrates the optical spectra of the TiO2-containing zinc phosphate glasses after gamma irradiation (8Mrad) and the spectral features can be summarized as follows; i.

The sample ZnPTi1 containing (0.25 % TiO2) reveals only an obvious increase of the intensity of the strong UV absorption and the resolution of a small broad visible band centered at about 560. 11

ii.

The samples ZnPTi2, ZnPTi3 and ZnPTi4 show the same spectral characteristics as before irradiation including the strong UV absorption exhibiting three peaks at about 240, 275, 310 nm together with the resolution of a strong broad visible band with two peaks at about 550 and 740 nm.

3.4. FT infrared absorption spectra of base and TiO2-containing lithium phosphate, lead phosphate and zinc phosphate glasses The infrared absorption spectrum of the base lithium phosphate glass (Fig. 3) reveals the following spectral characteristics: (a) A medium band with two peaks at about 450 and 485 cm-1. (b) A small peak at about 650 cm-1. (c) A small band at about 820 cm-1with three attached kinks at 720, 870 and 890 cm-1. (d) A very broad medium band with three peaks at about 900, 1020 and 1070 cm-1. (e) A broad and high intense band centered at about 1300 cm-1. (f) Eight small peaks are observed at 1620, 1680, 1750, 2280, 2320, 2460, 2880, 2930 cm-1. On introducing increasing TiO2 contents (0.25-2.5%), the main IR spectral bands remain almost unchanged in their position and number but minor variations of the intensities of some bands are observed Fig.(3). The infrared absorption spectrum of the base lead phosphate (Fig.4) reveals the following spectral features: 12

(a) A medium band with two peaks at about 465 and 520 cm-1. (b) Four small peaks at about 620, 640, 690, 780 cm-1. (c) A very broad connected medium band with three distinct peaks at about 880, 1050 and 1250 cm-1. (d) Five small peaks at about 1580, 1640, 1790 and 2820 and 2930 cm-1. On the addition of increasing TiO2 contents (0.25-2.5%), the main IR bands are persistent but the intensities progressively increase with the TiO2 content (Fig.4). The infrared absorption spectrum of the base zinc phosphate glass fig.(5) reveals the following spectral characteristics: (a) A small peak at about 405 cm-1. (b) A medium band with three peaks at about 460, 480 and 520 cm-1. (c) A medium band with two peaks at about 620 and 685 cm-1. (d) A medium band at about 750 cm-1 with two connected peaks at about 780 and 820 cm-1. (e) A very broad intense band with three distinct peaks at about 880, 1180 and 1275 cm1

and with three kinks at about 1060, 1300 and 1460 cm-1.

(f) A small peak at about 1640 cm-1. (g) Six small kinks at about 1900, 2200, 2350, 2420, 2860 and 2920 cm-1. On the introduction of increasing TiO2 contents (0.25-2.5%), the main IR bands remain in their position, number and intensity as before the addition of TiO2 (Fig.5). 13

4. Discussion 4.1. Interpretation of the UV absorption spectra in the base three different phosphate glasses The spectral measurements of the base lithium and zinc phosphate glasses reveal strong charge transfer ultraviolet absorption revealing mainly a single band at about 235 nm and with two attached subsidiary kinks at 220 and 250 nm. The base lead phosphate glass exhibits a broad ultraviolet spectrum consisting of two bands at 230 and 275 nm and followed by a small peak at about 340 nm. All the three varieties of the base phosphate glasses show no visible bands. Sigel and Ginther [21], Cook and Mader [22] have separately identified the appearance of charge transfer ultraviolet absorption bands in optical measurements of many commercial glasses and they have attributed such UV absorption bands to originate from unavoidable trace iron impurities within the raw materials used for preparation of such glasses. This postulation is further supported by other authors [23, 24]. Moncke and Ehrt [16, 17] have recommended that the preparation of optical glasses for special recent applications necessitates the need for ultra pure materials free from trace impurities even in the ppm level especially ferric ions because it could impair the usefulness of recent optical glasses. Recently, ElBatal et al [25, 26] have experimentally verified that strong UV absorption spectra are identified in the spectra of various undoped phosphate 14

glasses. These strong UV bands are related to the presence of unavoidable trace iron impurities which contaminated the raw chemicals used for preparation of such phosphate glasses. It is therefore assumed that UV absorption spectra observed in the studied two base lithium phosphate and zinc phosphate glasses are entirely due to trace iron impurities within the raw chemical materials used for the preparation of such glasses. The base lead phosphate glass reveals extra broad UV absorption than that observed in lithium and zinc phosphate glasses. This is due to the presence of divalent lead ions (Pb2+) in appreciable percent which are assumed to produce specific ultraviolet absorption as evidenced by several publications [23, 25, 26]. Duffy et al. [23, 27, 28] have assumed that the ultraviolet spectrum of the divalent lead ions (Pb2+) in oxide or fluoride glasses consists of bands arising from the 6s2 → 6s 6p transitions, the lowest energy corresponding to the frequency ν of the 1s0 → 3p1 band. It is thus concluded that the surplus UV absorption band observed at about 340 nm in the undoped lead phosphate glass is attributed to the sharing of the divalent (Pb2+) ions together with the other UV bands due to trace iron impurities.

4.2. Interpretation of the optical spectra of TiO2- containing samples Titanium ions are known to be able to exist in glasses in two valence forms, namely the trivalent (Ti3+) and tetravalent (Ti4+) states [29]. The ratio of each state in glass depends on the type and composition of glass and condition of melting. In alkali silicate 15

and alkali borate glasses melted under normal atmospheric condition, the tetravalent (Ti4+) ions are found to be predominant and the glasses are almost colorless especially in the doping level because the colored Ti3+ ions are very low. Ti4+ ions belong to the 3d0 configuration and did not exhibit d-d absorption bands and are expected to show an ultraviolet band. Ti3+ ions belong to 3d1 configuration which predicts that the spectrum of trivalent titanium ion is characterized by a single absorption band at 480-570 nm which is assigned to 2B2g → 2B1g transition [30] and alkali lithium glasses are colored violet or pink due to the abundant trivalent titanium (Ti3)+ ions. Some scientists [31, 32] have assumed a tetragonal distortion of the octahedral ligands around trivalent titanium ions and hence the subsequent observation of two peaks at about 570 and 680 nm. Titanium ions being d1, should certainly exhibit the Jann-Teller effect and hence produce the observed bands. Bausa et.al [33] have postulated that a further band is identified in some glasses at about 440 nm and can be assigned to a charge transfer transition between Ti3+ and Ti4+ ions. However, no further confirmation has been reached yet for this postulation.

4.3. Contribuation of the effect of gamma irradiation on the optical spectra of the base three phosphate glasses. 4.3.1. Lithium phosphate glass Previous irradiation studies on alkali and alkaline earth phosphate glasses have been summarized in the review articles by Lell et al [34], Bishay [14], and Friebele [15]. 16

Bishay [14] shows that the induced absorption in alkali phosphate glasses can be resolved into four bands centered at 2.3 eV(∼ 540 nm), 2.9 eV (∼ 420 nm), 5.5 eV (∼225 nm) and 6.0 eV (∼200 nm). The UV induced bands are correlated with electron trap centers while the visible induced bands are proposed to be related to positive hole centers. In a later contribution by Moncke and Ehrt [16, 17], many irradiation induced defects are identified by the deconvolution method of the optical spectra in variable phosphate glasses, Such authors have assumed that induced defects in glasses are formed in pairs of negative electron centers (EC) and positive hole centers (HC). They have further assumed that the two iron states even when present as impurities can be affected by irradiation; Fe2+ can be photo-oxidized to (Fe2+)+ and Fe3+ can be photoreduced to (Fe3+)-. Such oxidation-reduction variations produce induced color centers and can be identified by optical absorption. ElBatal et al [9, 25] have recently reached the conclusion that the creation of induced defects or the increase in the intensity of the UV bands with gamma irradiation is correlated mostly with the photochemical transformation of some Fe2+ ions to Fe3+ ions by capturing positive holes generated through the irradiation process. They have also correlated the visible induced bands observed in the spectra of phosphate glasses to positive hole centers attached to the phosphate network. Based on previous postulations, the observed induced defects in the studied base lithium phosphate glass which extend within both UV-visible regions can be correlated 17

with the same interpretation. It is suggested that the induced bands in the UV region are correlated with defects generated through photochemical reactions with trace iron impurities. The induced visible bands are due to the effect of gamma irradiation on the base lithium phosphate glass itself through the formation of positive hole centers (POHCs and OHCS as mentioned by previous authors [9, 10, 14, 15, 26]. The presence of Li+ ions in network modifying sites and this promotes the formation of nonbridging oxygens which are favorable sites for the generation of such positive hole induced defects.

4.3.2. Lead phosphate glass Gamma irradiation on the base lead phosphate glass produces induced defects in the UV region while the visible spectrum shows resistance or retardation to irradiation keeping the spectral curves almost unaffected. This interesting experimental result indicates and confirms that high lead glasses possess the capability to resist the effect of gamma irradiation to a measurable value and specifically within the visible region of the spectrum. The observed variations upon gamma irradiation are restricted to the absorption within the UV region. This behavior is assumed to be correlated with proposed photochemical reactions to both trace iron impurities and divalent lead Pb2+ ions. These proposals are virtually responsible for the formation of the broad UV absorption upon gamma irradiation.

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The previous interpretations are based on previous assumptions by some authors [14, 15] that some of the Fe2+ ions present in the glass capture positive holes during the irradiation process and are oxidized or transformed to Fe3+ which contribute to the increase in the intensity of the induced UV bands. The same holds for the absorption due to divalent lead ions. Friebele [15] has summarized the radiation induced defects which are generated in PbO containing silicate, borate and phosphate glasses. Friebele [15] has introduced the assumption that in high lead oxide glasses, Pb2+ ions are situated as mainly covalently bonded PbO4 units as glass formers. He also further postulated that the induced bands created by irradiation are correlated with the forming of Pb3+ ions in high lead glasses as previously suggested also by Bishay [14]. No spectral changes were observed with the newly formed Pb3+ ions and further studies are needed to confirm such assumption.

4.3.3. Zinc phosphate glass The induced spectrum of the zinc phosphate glass is observed to resemble that obtained from the lead phosphate glass. Also, the effect of gamma irradiation is restricted to the UV region. The observed results can be related to the ability of ZnO to form structural building ZnO4 units as PbO4 units from PbO [9, 35]. Such suggested structural building groups are expected to give strength and compactness to the glass network. Thus, the specific role of ZnO is similar to that of PbO and is assumed to be due to the coherence of the glass network by the formation of additional ZnO4 units. This is the reverse effect observed with the lithium phosphate glass as it is known that 19

Li+ ions occupy interstitial modifying positions and hence the formation of non-bridging ions. The non-bridging ions are known to be favorable sites for the formation of induced visible defects within the phosphate network.

4.4. Infrared absorption spectra and glass composition constitution There are five main points or parameters which must be mentioned and taken into consideration before detailed interpretation of the experimental FTIR results, These points are concerning interrelation between IR and phosphate glass constitution and are summarized as follows; 1. The IR phosphate group vibrations are dominant in all studied three different glasses because the host glass in all cases possesses the same anionic phosphate component. 2. The presence of three different cationic partners (Li+, Pb2+ and Zn2+) are expected to define to some extent the types of phosphate groups. This is naturally because these cations differ in their housing in the respective glass network. Li+ cations are solely modifier ions while Pb2+ and Zn2+ cations behave both as modifier and former ions within the glass network. 3. The IR spectra from lead phosphate and zinc phosphate glasses are therefore observed to be almost similar and quite different than the spectra of lithium phosphate glasses [35].

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4. The experimental IR spectra are expected to contain overlapping of some structural phosphate units vibrations because of the ability of P2O5 to form numerous structural groups [35-41]. 5. The network structure of phosphate glass is reported by most scientists [36-41] to contain a polymeric arrangement consisting of PO4 tetrahedral units. In the case of vitreous P2O5, the PO4 groups are connected to adjacent units by three of their four vertices; one place is occupied by a terminal, double-bonded oxygen atom. Although the structure of P2O5 is modified with the addition of alkali oxides (or divalent oxides), the phosphorus retains 4-fold coordination throughout the composition range from pure P2O5 to the fully saturated orthophosphate. The addition of alkali or divalent oxides to phosphate glasses, generally results in conversion of the three-dimensional network to linear phosphate chain [36-40]. This linear chain structure results in cleavage of P-O-P linkages and the creation of NBOs in the glass. 6. It is the (PO2), (PO3) and (PO4) groups, rather than separate P=O and P-O groups, that manifest themselves in the vibrational spectra of meta-, pyro-, and orthophosphate glasses.

4.5. Interpretation of the IR absorption spectra of base and TiO2-containing phosphate glasses.

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4.5.1. Interpretation of the IR spectra of base and TiO2-containing lithium phosphate glass

It is observed that mid region of the IR spectrum consists of some doublet bands at 440-550 cm-1, 750-800 cm-1 and 880-1200 cm-1 followed by a strong band centered at about 1300 cm-1. The detailed assignments are summarized as follows [36-41]; a) It is reported that the bands at 440-480 cm-1 are assigned to the bending vibrations of O-P-O units, (PO2) modes of (PO2)n chain group and the band at about 500 cm1

is related to fundamental frequency of (PO4)3 or as the frequencies of the P=O

bending vibrations. b) The peak at 725-760 cm-1 may be attributed to the symmetric stretching vibrations of P-O-P chains. c) The absorption bands in the region 800-1000 cm-1 are related to different metaphosphate groups. d) The strong band at 1060-1100 cm-1 is attributed to asymmetric stretching vibrations of P-O-P groups. e) The strong band at 1250-1300 cm-1 is related to the PO2 asymmetric stretching. The experimental result indicates that the addition of TiO2 (0.25-2.5%) causes some limited changes which can be correlated with the following parameters: i)

The increase of the covalent character of the P-O bonds by the addition of TiO2 or the formation of P-O-Ti bonds.

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ii)

Structural changes due to the addition of TiO2 and the formation of shorter chains and the possible formation of separate Ti-O units.

4.5.2. Interpretation of the IR spectra of undoped and doped both lead phosphate and zinc phosphate glasses.

The IR spectra of the two base lead phosphate and zinc phosphate glasses are very similar in their spectral characteristics and somewhat different than the IR spectrum of lithium phosphate. The reason for such difference is that both PbO and ZnO are assumed to be able to form structural units (PbO4 and/or PbO3) and ZnO4 which strengthen the network. This leads to the observed combination of the IR vibrations from 800-1400 cm1

in both the two mentioned lead and zinc phosphate glasses. The observed IR bands can be interpreted on the following basis [38-42]: a) The medium band at 475-490 cm-1 is assigned to the bending vibrations of O-P-O units and the PO2 modes. b) The peak at 505-510 cm-1 is related to the fundamental frequency of (PO4) groups. c) The band at 680-710 cm-1 is related to different metaphosphate groups. d) The band at 820-880 cm-1 is related to different metaphosphate groups. e) The band at 1010-1050 cm-1 is related to the asymmetric stretching of P-O-P group. f) The strong band at 1220-1270 cm-1 is attributed to the PO2 asymmetric stretching of the doubly bonded oxygen vibrations P=O modes. 23

g) The small peaks at 1640 and 1800 cm-1 are related to OH, H2O vibrations. Some authors [19, 42-43] have assumed that the IR spectra of glasses containing high PbO content should exhibit the sharing of the Pb-O or Pb-O-P vibrations within the range 400-650 cm-1. The addition of TiO2 within the level (0.25-2.5%) is observed to cause minor effect on the intensity of the IR bands. This can be attributed to the stability of the network containing additional structural units. TiO2 can share in the formation of structural units such as P-O-Ti or some Ti-O units upon the increase of TiO2 but the effect is limited due to the low level of TiO2 added. Also, a possible depolymerization effect due to the addition of TiO2 which leads to breaking of phosphate chain and formation of shorter chains. The observed FTIR of lithium phosphate, lead phosphate and zinc phosphate glasses according to different authors can be collected as follows as shown in table 2;

5. Conclusions Undoped and TiO2 containing lithium metaphosphate, lead metaphosphate and zinc metaphosphate glasses have been prepared and characterized by collective UVvisible and infrared spectroscopic measurements. The same spectral measurements have been repeated after gamma irradiation with a gamma dose of 8 Mrad. Experimental spectral data for base glasses show strong charge transfer absorption bands which are attributed to the presence of unavoidable trace iron impurities within 24

the materials used for the preparation of such glasses beside an extra band about 340 nm in the case of the lead metaphosphate glass due to the spectral contribution of divalent lead (Pb2+) ions. The addition of TiO2 to the three different phosphate glasses produces two characteristic visible bands which are related to the presence of distorted octahedral trivalent Ti3+ ions. Gamma irradiation of optical spectra of the base three different phosphate glasses shows induced bands which are mostly generated by photochemical reactions of trace iron impurities in the base phosphate glasses beside the divalent lead Pb2+ ions in the lead phosphate glass. In lithium phosphate glass, gamma irradiation produces an extra visible band due to positive hole centers (POHCs and OHCs) due to the sharing of nonbridging oxygens. Lead and zinc phosphate glasses are stable and did not produce induced visible bands. With TiO2-containing glasses, the induced bands are related to the sharing of the titanium ions and the glasses show some resistance or shielding towards gamma irradiation. The infrared absorption spectra of the studied phosphate glasses indicate the presence of phosphate units with metaphosphate groups as the main structural constituents, but the FTIR spectra of lead and zinc phosphate glasses are similar and somewhat combined spectra which are different from that for lithium phosphate glass. This difference is attributed to the ability of PbO and ZnO to form additional structural units. 25

Gamma irradiation is observed to decrease the intensities of some of the FTIR bands. Specially that due non-structural water, OH, POH vibrations. Such changes are assumed to be related to changes in the bond length and/or bond angles of the structural building units. Based on collective spectral data, it can be concluded that the TiO2-containing lithium phosphate glass is radiation sensitive and can be applied as glass dosimeter while both lead phosphate and zinc phosphate glasses are recommended as efficient radiation shielding candidates.

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6. References 1. A. Aronne, L.E. Depero, V.N. Sigaev, P. Pernice, E. Bontempi, O.V. Akimova, E. Fanelli, J. Non-Cryst. Solids 324 (2003) 208–219. 2. L. Koudelka, P. Mosner, J. Pospisil, L Montagne, G. Palavit, J. Solid State Chem.,178(2005)1837-1843. 3. G. Westin, A. Ekstrand, E. Zangellini, L. Börjesson, J. Phys. Chem. of Solids, 61(1)(2000)67-74. 4. L. Koudelka, P. Mosner, M. Zeyer, C. Jager, J. Non-Cryst. Solids, 326-327 (2003) 72– 76. 5. A. Saranti, I. Koutselas, M.A. Karakassides, J. Non-Cryst. Solids, 352 (2006) 390–398. 6. D. Carta, D. Qiu, P. Guerry, I. Ahmed, E. A. Abou Neel, J. C. Knowles, M. E. Smith, R. J. Newport, J. Non-Cryst. Solids, 354 (2008) 3671–3677. 7. G. Guo, Glass Technol., 39(1998)138. 8. S.W. Martin, Eur. J. Solid State Inorg. Chem., 1(1998)138. 9. F. H. ElBatal, M.A. Marzouk, A.M. Abdelghany, J. Non-Cryst. Solids, 357(2011)10271036. 10. H.A. ElBatal, A.M. Abdelghany, F.H. ElBatal, Kh. M. ElBadry, F.A. Moustaffa, Physica B, 406(9)(2011) 3694-3703. 11. L.E. Bausa, J.G. Sole, A. Duran, J.M.F. Navaro, J. Non-Cryst. Solids, 127(1991)267272. 12. S.Y. Marzouk, F.H. ElBatal, Nucl. Instr. Meth. Phys. Res. B, 248(2006)90-102.

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13. A. Agarwal, V.P. Seth, P. Gahlot, D.R. Goyal, M. Arora, S.K. Gupta, Spectrochim. Acta A, 60(13)( 2004) 3161-3167. 14. A. Bishay, J. Non-Cryst. Solids, 3(1)( 1970)54-114. 15. E.J. Friebele, P.205 in:”Optical absorption of glass” E.D. D.R. Uhlamann and N.J. Kreidl, American Ceramic Society, Westerville, OH, USA (1991). 16. D. Moncke, D. Ehrt, Optical Materials, 25(2004) 425-437. 17. D. Moncke, D. Ehrt, J. Non-Cryst. Solids, 352(2006)2631-2636. 18. F.H. Elbatal, Nucl. Instr. Meth. Phys. Res. B, 265(2007)521-535. 19. F.H. ElBatal, S.Y. Marzouk, J. Mater. Sci., 44(2009)3061-3071. 20. N.A. Ghoniem, H.A. ELBatal, A.M. Abdelghany, I.S. Ali, J. Alloys and Compound, 509(2011)6913-6919. 21. G.H. Sigel, R.J. Ginther, Glass Technol., 9(1968)66. 22. L. Cook, K.H. Mader, J. Amer. Ceram. Soc., 109(1982)65. 23. J.A. Duffy, Phys. Chem. Glasses, 38(1997)289. 24. D. Ehrt, P. Ebeling, U. Natura, J. Non-Cryst. Solids, 263-264(2000)240. 25. F.H. ElBatal, J. Mater. Sci. 43(2008)1070. 26. F.H. ElBatal, A.M. Abdelghany, R.I. Elwan, J. Mol. Struct., 1000(1-3)(2011)103-108. 27. J.A. Duffy, M.D. Ingram, J. Inorg. Nucl. Chem., 37(1975)1203. 28. J.A. Duffy, M.D. Ingram, J. Non-Cryst. Solids, 21(1976)373. 29. T. Bates, P.195 in “Modern Aspects of the Vitreous State”, Vol. 2, Ed. J.D. Mackenzie, Butterworths, London (1962). 30. C.R. Bamford, Color Generation and Control in Glass, Glass Science and Technology, Elsevier scientific publishing company, Amsterdam, (1977). 28

31. N. Abdel Shafi, M.M. Morsi, J. Mater. Sci., 32(1997)5185. 32. B.V. Raghavaiah, C. Laxmikenth, N. Verraiah, Opt. Comm., 235(2004)341. 33. L.E. Bausá, J. G. Solé, A. Durán, J.M. Fernández Navarro, J. Non-Cryst. Solids, 127(3)(1991)267-272. 34. L. Lell, N.J. Kreidl, J.R. Hensler, in; J.D. Burke (Ed.) Progress in Ceramic Science, Vol. 4, Pergamon Press, London (1966) pp 1-93. 35. A.M. Abdelghany, Silicon, 2(3)(2010)179-184. 36. Y.B. Peng, D.E. Day, Glass Technol., 5(1984)166. 37. B.C. Bunker, G.W. Arnold, J.A. Wilder, J. Non-Cryst. Solids, 64(1984)291. 38. A. Chahine, M. El-Tabirou, M. El-Baniasici, M. Haddad, J.I. Pascal, Mater. Chem. Phys., 84(2004)41.

39. P. Znacik, M. Jamnicky, J. Non-Cryst. Solids, 146(1992)74. 40. L. Montage, C. Palavit, G. Mairesse, Phys. Chem. Glasses, 37(1996)200. 41. Y.M. Moustafa, K. El-Egili, J. Non-Cryst. Solids, 240(1998)144. 42. K. Witke, U. Harder, M. Willifahrt, T. Hubert, P. Reich, Glastech. Ber. Glass Sci. Technol. 69(1996)143.

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29

1.2

1.0

0.8

Absorbance

Absorbance (a.u.)

1LiP 2MR 6MR 8MR

0.6

0.4

0.2

0.0 200

400

600

800

1000

1200

1400

-1

Wavenumber (cm )

250

500

750

1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

(a) Lithium phosphate

Absorbance (a.u.)

PbP 2MR 6MR 8MR

1.0 0.9 0.8 0.7

Absorbance

0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 200

250

300

350

400

450

Wavelength(nm)

250

500

750

1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

(b) Lead Phosphate

30

ZnP 2MR 6Mr 8MR

1.0 0.9 0.8

Absorbance (a.u.)

Absorbance

0.7 0.6 0.5 0.4 0.3 0.2 200

250

300

350

400

450

500

Wavelength (nm)

250

500

750

1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

(c) Zinc phosphate Figure (1) Optical absorption spectra of the three base phosphate glasses before and after gamma irradiation with their analyzed normalized spectra .

3.5

3.5

LiPTi1 LiPTi2 LiPTi3 LiPTi4

3.0

2.5

Absorbance

Absorbance

2.5 2.0 1.5

2.0

1.5

1.0

1.0

0.5

0.5 0.0 200

LiPTi1 LiPTi2 LiPTi3 LiPTi4

3.0

0.0

300

400

500

600

700

800

900

200

1000

300

400

500

600

700

Wavelength (nm)

Wavelength (nm)

(a)

(b)

31

800

900

1000

3.5

3.5

PbPTi1 PbPTi2 PbPTi3 PbPTi4

3.0

2.5

Absorbance

Absorbance

2.5 2.0 1.5 1.0

2.0 1.5 1.0

0.5 0.0 200

PbPTi1 PbPTi2 PbPTi3 PbPTi4

3.0

0.5

300

400

500

600

700

800

900

0.0 200

1000

300

400

Wavelength (nm)

500

(c)

800

3.5

ZnPTi1 ZnPTi2 ZnPTi3 ZnPTi4

3.0

900

1000

ZnPTi1 ZnPTi2 ZnPTi3 ZnPTi4

3.0

2.5

2.5

Absorbance

Absorbance

700

(d)

3.5

2.0 1.5 1.0

2.0 1.5 1.0

0.5 0.0 200

600

Wavelength (nm)

0.5

300

400

500

600

700

800

900

0.0 200

1000

Wavelength (nm)

300

400

500

600

700

800

Wavelength (nm)

(e) (f) Figure (2) Optical absorption spectra of the TiO2-doped three phosphate glasses before and after gamma irradiation.

32

900

1000

Absorbance (a.u.)

LiPTi3

LiPTi3 LiPTi2

LiPTi1

Base LiP

2400 2200 2000 1800 1600 1400 1200 1000 800

600

400

-1

Wavenumber (cm ) Fig.(3) FTIR spectra of undoped and TiO2-doped lithium phosphate glasses

Absorbance (a.u.)

PbPTi4

PbPTi3

PbPTi2

PbPTi1

Base PbP

2400 2200 2000 1800 1600 1400 1200 1000 800

600

400

-1

Wavenumber (cm )

Fig.(4) FTIR spectra of undoped and TiO2-doped lead phosphate glasses

33

Absorbance (a.u.)

ZnPTi4

ZnPTi3

ZnPTi2 ZnPTi1 Base ZnP

2400 2200 2000 1800 1600 1400 1200 1000 800

600

400

-1

Wavenumber (cm ) Fig.(5) FTIR spectra of undoped and TiO2-doped zinc phosphate glasses

34

Table (1) Chemical Composition of the prepared glasses Sample P2O5 LiPTi1 LiPTi2 LiPTi3 LiPTi4 PbPTi1 PbPTi2 PbPTi3 PbPTi4 ZnPTi1 ZnPTi2 ZnPTi3 ZnPTi4

50 50 50 50 50 50 50 50 50 50 50 50

Li2O PbO ZnO mol % 50 50 50 50 50 50 50 50 50 50 50 50

35

Added (wt%) TiO2 Al2O3 0.25 0.5 0.50 0.5 0.75 0.5 2.50 0.5 0.25 0.5 0.50 0.5 0.75 0.5 2.50 0.5 0.25 0.5 0.50 0.5 0.75 0.5 2.50 0.5

Table 2; IR peak assignment of the structural building unit in the three glass systems.

Lithium phosphate glass Peak position cm 450 485 720 820-890 1020 and 1070 1260-1300 1640 to 2930

-1

Asignement Bending vibrations of P-O-P PQ2 modes of PO2 chain symmetric stretching vibrations of P-O-P rings different metaphosphate groups asymmetric stretching of P-O-P groups broad and intense band attributed to the (PO2) asymmetric stretching of the doubly bonded oxygen vibrations (P=O) small peaks related to water, OH.

Ref. 9, 12 25, 26 9, 12, 40, 41 9, 42, 43 9, 12 9, 12 40-43 9, 25, 41

Lead phosphate and zinc phosphate glasses 460, 480, 520 685, 720-750 880 1020 and 1180 1275-1300 1640-2930

bending vibrations of O-P-O units and the PO2 modes and sharing of Pb-O units symmetric stretching vibrations of P-O-P rings to metaphosphate group asymmetric stretching of P-O-P groups PO2 asymmetric stretching of the doubly bonded oxygen vibrations vibrations of H2O, OH

36

9, 12, 42-45 9, 12, 40, 41 9, 42, 43 9, 12 9, 12 40-43 9, 25, 41

Highlights Three series of different phosphate glasses doped with varying amount of TiO2 were prepared.  Effect of successive gamma ray irradiation in prepared glass structure was studied.  FTIR, UV measurement before and after gamma irradiation were studied.

 UV spectra reveal some changes with different gamma doses which are discussed.

37