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Silicon (2013) 5:283–295 DOI 10.1007/s12633-013-9160-4

ORIGINAL PAPER

Optical Properties and Effect of Gamma Irradiation on Bismuth Silicate Glasses Containing SrO, BaO or PbO M. A. Marzouk · H. A. ElBatal · F. M. Ezz ElDin

Received: 13 January 2013 / Accepted: 4 July 2013 / Published online: 4 October 2013 © Springer Science+Business Media Dordrecht 2013

Abstract Optical and Fourier Transform Infrared spectroscopic measurements have been utilized to investigate and characterize binary bismuth silicate glasses together with derived samples by replacement of parts of the Bi2 O3 by SrO, BaO, or PbO. This study aims to justify and compare the spectral and shielding behavior of the studied glasses containing heavy metal ions towards gamma irradiation. The study also aims to measure or calculate the optical energy band gap of these glasses. The replacement of parts of the Bi2 O3 by SrO, BaO or PbO caused some changes within the optical and infrared absorption spectra due to the different housing positions and physical properties of the respective divalent Sr2+ , Ba2+ and Pb2+ ions. The stability of both the optical and infrared spectra of the studied bismuth silicate glasses and related samples towards gamma irradiation confirm some shielding behavior of the studied glasses and their suitability as radiation shielding candidate materials. Keywords Bi2 O3 · SiO2 glasses · Infrared spectroscopy · Optical properties · Radiation damage

1 Introduction The behavior of glasses exposed to radiation is of the utmost importance and of recent interest since they are used as M. A. Marzouk · H. A. ElBatal () Glass Research Department, National Research Center, Dokki, Cairo, Egypt e-mail: h [email protected] F. M. Ezz ElDin National Center for Radiation Research and Technology, Nasr City, Cairo, Egypt

lenses, windows and other optical elements in a large number of optical devices used in radiative environments [1]. The optical absorption bands induced by irradiation depend on the number of parameters including the type and dose of irradiation, composition of the glasses, and the presence of different dopants or impurities. The presence of heavy metal ions (e.g. Pb2+ or Bi3+ ), transition metal ions (e.g. 3d ions, Mo6+ or W6+ ), and rare earth metal ions (e.g. cerium ions) have been recognized to change or even suppress the effects of irradiation [1–6]. Nevertheless, comprehensive studies of the irradiation on simple binary alkali borate, alkali silicate and alkali phosphate glasses have resulted in a relatively unified understanding of induced radiation damages in various glasses as illustrated in the review articles by Lell et al. [2], Bishay [3] and Friebele [4]. Careful inspection of the induced bands from the mentioned three glass systems reveals that the three resolved bands centered in the 2.0 to 2.3 eV, near 2.9 to 3.0 eV and at 5.1 to 5.5 eV are common to all three glasses. Only the 4.0 eV band in the silicate glass appears missing from the borate and phosphate analogues [1–4]. Ehrt and colleagues [5–7] have extensively studied various phosphate and borosilicate optical glasses containing transition metal and rare earth metal ions and have identified the induced bands generated by irradiation. They have stressed the need to use ultrapure materials for the preparation of specific optical glasses to avoid the appearance of charge transfer UV absorption bands due to trace iron impurities even at the ppm level, which could impair the usefulness of the optical glasses. ElBatal et al. [8–12] have recently studied various types of undoped silicate, phosphate and borate glasses and those containing 3d transition metal ions and have identified experimentally the UV absorption bands due mostly to Fe3+ ions–impurities unavoidably present as impurities within the raw materials

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used for the preparation of these various glasses. They have identified and differentiated between the induced bands due to intrinsic defects within the glass itself and induced bands due to extrinsic defects due to the presence of the impurities or introduced dopants. ElBatal et al. [13–16] have recently studied Bi2 O3 –containing glasses including bismuth borates and bismuth silicates and have reached the conclusion that the presence of any of the heavy metal oxides Bi2 O3 and PbO, beside some 3d transition metal ions, WO3 or MoO3 , causes shielding behavior (or a retardation effect) towards progressive gamma irradiation. These authors have observed that the optical spectral curves remain very similar and without obvious changes after gamma irradiation to the optical curves before irradiation. Also, FTIR spectral data from the same glasses reveal that the main IR vibrational bands remain unchanged in their numbers and positions after gamma irradiation and only some limited variations may be observed in the intensity of some IR bands, specifically those due to water molecules or OH vibrations. They have reached the conclusion that glasses containing high Bi2 O3 concentrations are very suitable candidates to be used as radiation-shielding materials. Also, extensive studies by Singh et al. [17–19] have arrived at the same conclusion, reporting that high lead borate and lead silicate glasses with variable additives such as Bi2 O3 , ZnO and BaO are promising shielding glasses. The present work includes the preparation of a selected binary bismuth silicate glass of the nominal molecular composition Bi2 O3 70 % and SiO2 30 % with other derived glassy samples containing substituted 2 % or 5 % from SrO, BaO or PbO replacing equivalent Bi2 O3 . Optical and FTIR spectra of the prepared samples have been measured before and after being subjected to gamma irradiation. The induced spectra of the samples are derived and the data are realized and discussed to justify the observed induced bands and their origin in the studied glasses. Also, the optical band gap energy and Urbach energy were calculated and interpreted. This work aims to justify the shielding behavior of the studied glasses containing selected heavy metal oxides towards gamma irradiation.

2 Experimental Details 2.1 Preparation of the Glasses The glasses were prepared from chemically pure materials. The Bi2 O3 was introduced as such and silica was added in the form of pulverized quartz. The SrO and BaO were added in the form of their anhydrous carbonates and PbO was introduced in the form of red lead oxide (Pb3 O4 ). The chemical compositions of the prepared samples are given in Table 1.

Silicon (2013) 5:283–295 Table 1 Chemical composition of the studied glasses Sample

1 2 3 4 5 6 7

Chemical composition (mol %) Bi2 O3

SiO2

SrO

BaO

PbO

70 68 65 68 65 68 65

30 30 30 30 30 30 30

– 2 5 – – – –

– – – 2 5 – –

– – – – – 2 5

The accurately weighed batches were melted in a porcelain crucible at 1150 ◦ C for 1 h. The melts were cast into warmed stainless steel molds. The samples were crushed to a fine powder in an agate mortar and re-melted for another 30 min to achieve homogeneous and clear samples. The melts were cast into warmed stainless steel molds of the required dimensions. The prepared samples were immediately transferred to a muffle furnace regulated at 400 ◦ C for annealing. The annealing muffle was switched off after 1 hour and left to cool to room temperature at a rate of 25 ◦ C /hour. 2.2 UV-Visible Absorption Spectra The optical [UV-Vis] absorption spectra before and after gamma irradiation were measured at room temperature in the range 200 to 1000 nm using a computerized recording spectrophotometer (type T80t, PG Instrument Ltd., England). Highly polished samples of equal thickness [2 ± 0.1 mm] were used in these measurements. The same optical measurements were repeated after gamma irradiation with a dose of 10 M rad (= 10 × 104 Gy). 2.3 Infrared Absorption Spectra FT Infrared absorption spectra of the glasses were measured at room temperature in the range 4000–400 cm−1 using an Infrared spectrophotometer [type Mattson 5000 FTIR spectrometer] using the KBr disc technique. The samples were pulverized into a fine powder and then mixed with potassium bromide powder using a weight ratio of 1:100. The mixture was subjected to a load of 5 tons cm−2 in an evocable die for 2 min to produce clear homogenous discs. The IR absorption spectra were measured immediately after preparing the discs. The same spectral measurements were repeated after subjecting the powdered samples to gamma irradiation 10 M rad (= 10 × 104 Gy).

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2.4 The Irradiation Facility A 60 Co gamma cell [2000 Ci] was used as the gamma ray source with a dose rate of 1.5 Gys−1 (150 rads−1 ) at a temperature of 30 ◦ C. The investigated glasses were subjected to the same total gamma dose every time.

3 Results 3.1 Optical Absorption Spectra Before and After Gamma Irradiation Figure 1 illustrates the UV-Visible absorption of the studied base bismuth silicate glasses. The base binary bismuth silicate glass shows a spectrum consisting of strong UVnear visible absorption revealing four peaks at 262, 346 and 424 nm. No further visible bands could be identified. The intensity of the peaks decreases with increasing wavelength. Figure 2 illustrates the optical absorption spectra of bismuth silicate glasses containing three substituted heavy metal oxides SrO, BaO or PbO before irradiation. The optical spectral results indicate that the introduction of 2 % or 5 % oxides (replacing equivalent Bi2 O3 ) causes mostly broad bands extending from 200 to about 550 nm, with variable changes summarized as follows: (a)

(b)

The introduction of 2 or 5 % SrO causes the resolution of four peaks at 238, 316, 485 and 537 nm with the peak at 485 nm possessing the highest intense absorption. The 5 % SrO sample optical spectral curve is completely parallel to the spectrum of the 2 % SrO sample with a slight increase all over the entire spectrum and with the same absorption peaks. The introduction of 2 % or 5 % BaO causes the resolution of four absorption peaks at 235, 325, 494 and

Fig. 2 UV-Visible absorption spectra of SrO, BaO or PbO doped bismuth silicate glasses before gamma irradiation

Fig. 1 UV-Visible absorption spectra of undoped bismuth silicate glasses before and after 10 M rad gamma irradiation

541 nm with the peak at 494 nm possessing the highest and most intense absorption. The glass containing 5 % BaO reveals exactly the same absorption curve as that for the 2 % BaO glass with the same peaks but with higher intensity.

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(c)

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The introduction of 2 % or 5 % PbO causes the resolution of three absorption peaks at 235, 390, and 535 nm. It is evident that the glass containing 5 % PbO exhibits the same spectral behavior but the last two peaks move to slightly longer wavelengths.

Figure 3 illustrates the optical absorption spectra of the studied glasses after subjecting all of the samples to a gamma dose of 10 M rad (= 10 × 104 Gy). The studied samples reveal the following optical responses after gamma irradiation: (a)

(b)

(c)

absorption. Specifically n = 1/2 for an allowed direct transition, n = 3/2 for a forbidden direct transition, n = 3 for forbidden indirect transition, and n = 2 referring to indirect allowed transitions [22]. Using the previous Eq. (1), by plotting (αhν)1/2 as a function of the photon energy hν, one can find the

The two glasses containing SrO after gamma irradiation revealed four induced sharp and strong bands at 212, 324, 370 and 525 nm. The glass containing substituted 5 % SrO reveals a slight increase in absorption within the positions of the peaks. The two glasses containing BaO reveal after irradiation, three induced bands, the first band is exceptionally broad and intense, extending from 200 to about 475 nm and centered at 344 nm followed by two medium bands decreasing in intensity and with peaks at 513 and 565 nm. The two glasses containing PbO after gamma irradiation revealed four induced bands, the first band is broad nearly symmetrical with high intensity and extending from 200 to about 380 nm and centered at 285 nm. The second and fourth bands are medium intensity and sharp with peaks at 393 and 542 nm. The third band is small and broad centered at 462 nm.

3.2 Optical Band Gap Energy (Eopt ) and Urbach Energy (E) The study of the fundamental absorption edge in the UVregion is a useful method for investigating the optical transition and electronic band structure in crystalline and non-crystalline materials. There are two types of optical transitions which can occur at the fundamental absorption edge of crystalline and non-crystalline semiconductors, they are direct and indirect transitions. In both the cases, electromagnetic waves interact with the electrons in the valence band, which are raised across the fundamental gap to the conduction band [20]. Mott and Davis [21] have suggested the following expression for the relationship between the optical band gap, absorption coefficient and energy (hv) of the incident photon: αhv = B(hv − Eopt )n

(1)

Where Eopt is the optical energy gap, B is a constant called the band tailing parameter and n is an index which can be assumed to have values of 1/2, 3/2, 2 and 3, depending on the nature of the electronic transition responsible for the

Fig. 3 UV-Visible absorption spectra of SrO, BaO or PbO doped bismuth silicate glasses after 10 MR gamma irradiation

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Fig. 4 (αhν)1/2 as a function of photon energy (hν) for the base glass (a) before and (b) after 10 M rad gamma irradiation

optical energy band gaps (Eopt ) for an indirect transition by extrapolating the linear region of the curves to the hν axis. The data are shown in Figs. 4, 5 and 6. The Urbach energy gives the width of the tails of the localized states within the optical band gap [23]. The dependence of the absorption coefficient in the region of lower photon energy of the absorption edge can be described by the formula [23]:   hν α(ν) = B exp (2) E where B is a constant, E is the Urbach energy and ν is the frequency of the radiation. Plots were also drawn between ln(α) and hν (Eq. 2) and from these plots, the value of the Urbach energy E can be calculated from the reciprocal of the slope of the linear region of such plots. The data are listed in Table 2. 3.3 Infrared Absorption Spectra Before Irradiation Figures 7, 8 and 9 illustrate the FTIR spectra of the base binary bismuth silicate glass and other derived glasses

Fig. 5 (αhν)1/2 as a function of photon energy (hν) of SrO, BaO or PbO doped bismuth silicate glasses before irradiation

containing substituted parts of SrO, BaO or PbO instead of the equivalent Bi2 O3 before gamma irradiation. The IR spectrum of the binary bismuth silicate glass is observed to consist of three main broad absorption bands within the region from 400 to 1200 cm−1 and are then

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Silicon (2013) 5:283–295 Table 2 Optical parameters of some selected samples Sample

Base 5 % SrO 5 % BaO 5 % PbO

2. 3.

4. 5. 6.

Eopt (cm−1/2 eV1/2 )

E (eV)

0 MR

10 MR

0 MR

10 MR

2.19 1.50 1.48 1.55

1.34 1.18 1.19 1.20

0.63 0.38 0.54 0.28

0.97 0.95 0.79 0.53

main peak at about 482 cm−1 with three neighboring connected peaks, one at the ascending lobe at about 460 cm−1 and two peaks at the descending lobe at about 515 and 560 cm−1 . A small separate peak is identified at about 680 cm−1 . A second main broad band is centered at about 871 cm−1 and with two small attached peaks at about 740 cm−1 and about 900 cm−1 . A third main broad band is centered at about 1095 cm−1 with an attached peak at about 1020 cm−1 . Five small peaks are observed at about 1285, 1407, 1500, 1639 and 1440 cm−1 . The near-IR spectrum reveals two small peaks at about 3730 and 3800 cm−1 .

Fig. 6 Figure 5: (αhν)1/2 as a function of photon energy (hν) of SrO, BaO or PbO doped bismuth silicate glasses after 10 MR gamma irradiation

followed by five small peaks and finally with two peaks in the near–IR region. The detailed IR absorption spectrum of the base binary bismuth silicate glass is outlined as follows: 1. The first far-IR broad band originates at the beginning of the measurements at 400 cm−1 and exhibits a

Fig. 7 Infrared absorption spectra of the undoped and SrO–doped bismuth silicate glasses before gamma irradiation

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Fig. 8 Infrared absorption spectra of undoped and BaO–doped bismuth silicate glasses before gamma irradiation

The replacements of 2 % or 5 % Bi2 O3 by one the oxides SrO, BaO or PbO reveal obvious different IR spectral changes which are highly prominent especially with the introduction of lead oxide. The IR spectral characteristics of the derived substituted glasses are summarized as follows: 1. The introduction of 2 % or 5 % SrO replacing Bi2 O3 shows only some limited variations with the first replacement identified by the increase of the two main bands and with the combination of the third band with the second band. 2. The introduction of 2 % or 5 % BaO replacing Bi2 O3 causes minor changes in the IR spectra. The three main bands remain identified with minor variations in their positions. The third band in the first replacement 2 % BaO is extended with a linking attached peak at about 1285 cm−1 . 3. The introduction of PbO causes major changes in the IR spectra depending on the percent added. With the introduction of 2 % PbO, the three main bands are observed to shift to shorter wavenumbers and the third band shifts to 1006 cm−1 with a marked decrease in intensity. With 5 % PbO, the intensities of the two bands highly increase with shifting to 470 and 863 cm−1 while

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Fig. 9 Infrared absorption spectra of undoped and PbO–doped bismuth silicate glasses before gamma irradiation

the third main band almost disappeared as a separate band and is only observed as an attached peak to the second band. 3.4 Effect of Gamma Irradiation on the FTIR Spectra Figures 10, 11 and 12 illustrate the infrared absorption spectra of the studied glasses after gamma irradiation with a dose of 10 M rad (= 10 × 104 Gy). Careful inspection and comparison with the IR spectral data before irradiation reveals that all the main vibrational bands remain almost unchanged in their numbers and positions. These results indicate that the base bismuth silicate glass and the prepared derived samples containing SrO, BaO or PbO possess marked shielding behavior towards gamma irradiation together with a distinct network structure stability.

4 Discussion 4.1 Interpretation of the Origin of UV-Near Visible Absorption Spectrum in Base Bismuth Silicate Glass Some glass scientists [24, 25] have identified strong ultraviolet absorption bands in various undoped commercial

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Fig. 10 Infrared absorption spectra of undoped and SrO–doped bismuth silicate glasses after 10 M rad gamma irradiation

Fig. 11 Infrared absorption spectra of undoped and BaO–doped bismuth silicate glasses after 10 M rad gamma irradiation

silicate glasses and they have assumed that such strong UV absorption bands have originated from the presence of unavoidable trace iron impurities contaminating the raw materials used for the preparation of the glass samples. Extensive studies on various optical phosphate and borosilicate glasses by Ehrt et al. [5–7] have reached the same conclusion. They have recommended using ultrapure materials for the preparation of special optical glasses because the presence of the UV absorption could impair the usefulness of the optical glasses. ElBatal et al. [26–30] have identified specific UV absorption bands in various undoped silicate, borate and phosphate glasses and they have related such UV absorption bands to the presence of trace iron impurities and specifically to ferric (Fe3+ ) ions within the chemicals used for the preparation of these special glasses. Glasses containing high contents of PbO or Bi2 O3 have been identified to exhibit extended UV absorption and in some instances the absorption spectra are extended to the near-visible region [13, 16]. Duffy and Ingram [31] and Duffy [32] have recognized and classified differently originated ultraviolet absorption in various glasses. Some transition metal ions (e.g. Fe3+ and Cr6+ ) in glasses exhibit characteristic charge

transfer ultraviolet absorption spectra even if present in the ppm level. Such metal ions in glass owe their UV spectra to an electron transfer mechanism. However certain other metal ions including Ce3+ , Tb3+ , U4+ as well as d10 s2 ions (such as Pb2+ and Bi3+ ) absorb radiation through electronic transitions involving orbitals essentially of the metal ion only. The name “Rydberg” has been suggested for such UV spectra to distinguish them from the common charge electron transfer spectra. Earlier, Paul [33] and Parke and Webb [34] identified an ultraviolet peak when traces of Bi3+ ions were added to borate and phosphate glasses and the transition of this peak was related to 1 S0 →3 P1 . Duffy and Ingram [31] agreed with this assignment. Reisfeld and Boehm [35] compared the UV absorption of Bi3+ ions in phosphate, borax and germanate glasses and showed that the UV absorption peak lies in the three glasses at 43,010, 41,322 and 36,764 cm−1 , respectively. However, some authors [36] observed that the color due to the bismuth (Bi3+ ) ions was not uniform and assumed that this color was probably due to particle separation and not due to a true solution. Feltz and Morr [37] have assumed that this color was caused by a very small liberation of oxygen from the melt at high temperature and that a few percent assumed a lower bismuth oxidation state.

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This specific UV peak at about 236 nm is related to trace iron impurities in various undoped silicate glasses [10]. The peak positions of the Bi3+ ions obtained by Denker et al. [40] are somewhat different than the peaks reached in our study. The reasons for this difference can be related to several reasons: (a) The different temperature of melting which is 1150 ◦ C in our study and 1850 ◦ C in the Denker et al. study including their assumption of the presence of Bi3+ ions at this elevated temperature due to the N2 atmosphere. (b) The difference in glass constituents, which in our work consists of 70 % Bi2 O3 and 30 % SiO2 , and in the work of Denker et al. consists of SiO2 , MgO, and Al2 O3 with some additions of Bi2 O3 (0.025, 0.05, 0.25). (c) The melting condition in our work is ordinary atmospheric air while the work by Denker et al. employed a nitrogen atmosphere. 4.2 Interpretation of the Effect of Divalent Oxides (SrO, BaO and PbO) on the Optical Spectra

Fig. 12 Infrared absorption spectra of undoped and PbO–doped bismuth silicate glasses after 10 M rad gamma irradiation

The present observed UV-near visible absorption bands have been measured for uniformly colored bismuth silicate glasses prepared by remelting for the second time the pulverized powder of the first prepared glassy samples after crushing. The same optical spectral bands have been previously identified by Sanz et al. [38] and ElBatal et al. [13–15, 30, 39] from high bismuth silicate and bismuth borate glasses. Based on previous considerations, the first strong charge transfer UV band observed at 236 nm in the base glass is related to iron impurities (Fe3+ ions) while the three successive UV-near visible bands at 360, 399, and 424 nm are related to the absorption contribution from Bi3+ ions. The detailed assignments of these bands necessitate further studies including corresponding analogues of crystalline Bi2 O3 compounds by combined recent techniques. A recent contribution by Denker et al. [40] on the optical spectra of MgO-Al2 O3 -SiO2 glasses, with different variable Bi2 O3 contents, has reached to some related results. The glasses were prepared in an iridium crucible at 1850 ◦ C in a nitrogen atmosphere. The spectra reveal the resolution of three peaks at 235, 450, and 650 nm. Denker et al. [40] have not introduced any spectral measurement for the base glass without bismuth ions to compare with the first UV peak in the spectrum of our base glass observed at 236 nm.

(i) The differences in the optical behavior of these specific divalent oxides depend on the type of environment for these oxides in the glass network. SrO and BaO are accepted to be solely occupying modifying positions within the glassy network while PbO demonstrates dual behavior, acting partly as a modifier and also forming structural units such as PbO4 and/or PbO3 [12–16, 29, 30]. (ii) The introduction of these oxides may change the number of nonbridging oxygens leading to the shifting of the UV-visible bands to higher wavelengths. SrO and BaO like alkali oxides introduce nonbridging oxygen ions during their additions while PbO is able to form structural units as well as being partly as a modifier oxide. (iii) SrO is known to exist within modifying sites and the compactness of the network becomes lower. Also, the replacement of a heavy metal oxide (Bi2 O3 ) by a relatively lower mass oxide (SrO) will initiate the freedom for generation of the absorption due to electronic transitions between orbital sites essentially on the same and also for charge transfer of an electron from the glass network to the metal ion (Fe3+ ). (iv) BaO is also of the same behavior as SrO, behaving as a modifier oxide but with relatively higher mass than SrO. The result of its introduction is the observation of compaction of some UV bands to form a composite band extending from 200 to about 470 nm and centered at 344 nm.

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(v) PbO is an exceptional multifunctional oxide capable of acting both as modifying oxide and also as a network–forming oxide. Several glass scientists [32– 34] have identified that the Pb2+ ion like Bi3+ ion is a member of the p-block s2 ions (6s→6p) and thus exhibits UV and sometimes extended to near visible bands. This explains the observed extended UV-near visible absorption of glasses containing PbO. Thus the collective optical spectra of glasses containing Bi2 O3 and PbO include the absorption due to collective trace iron impurities (Fe3+ ), beside divalent lead (Pb2+ ) ions and trivalent bismuth (Bi3+ ) ions. (vi) All the glasses containing substituted divalent oxides reveal the extension of the absorption to 562 nm. This may be attributed to the possible increase in nonbridging oxygens with the introduced divalent oxides. (vii) Ren et al. [41] have compared the effect of alkaline earth oxides (CaO, SrO and BaO) on the broad band infrared luminescence covering the 1,000–1,600 nm wavelength region from bismuth silicate glass. The peak position by the authors [41] is assumed to be adjusted by the species of the alkaline earth metal oxide in the glass and the fluorescent intensity decreases with the increase in the alkaline earth metal radius. 4.3 Interpretation of the Effect of Gamma Irradiation on the Optical Absorption of the Studied Glasses The optical absorption results (Fig. 1) show that on subjecting the base binary bismuth silicate glass to gamma irradiation (10 M rad), the overall spectra in the UV – near visible region decrease in intensity within the same region and the peak due to Fe3+ shifts from 236 to 290 nm. The other three peaks at 360, 391 and 424 nm, which are related to absorption of Bi3+ , remain nearly in position but with lower intensity. These results can be interpreted on the following basis: (a) Gamma irradiation produces pairs of electrons and positive holes. These pairs are reacted or trapped during the irradiation process by trace impurities, nonbridging oxygens, transition metals and other intrinsic defects already present before irradiation within the glass matrix [3, 4]. (b) It is suggested that some of the present Fe3+ ions capture electrons and are converted to Fe2+ ions. This explains the obvious decrease of intensity of the absorption band at 236 nm due to Fe3+ ions and its shifting to 290 nm. Fe2+ ions are known to have their main optical absorption sites at about 1,100 nm [8, 15].

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(c) The decrease of the intensity of the absorption bands within the positions previously identified to be due to Bi3+ ions can not be related directly to the decrease of Bi3+ content and the transformation to other valence states for bismuth ions because the other valence states of bismuth are assumed to be unstable [42]. The exact interpretation of this result necessitates further studies by combined techniques. Some authors [40, 41] have assumed that Bi3+ can undergo reduction to Bi+ or Bi atoms but no optical studies of these forms in glasses have been completely justified by published optical spectra. (d) The effects of gamma irradiation on the six substituted glasses are observed to be of a peculiar different nature and vary with the type of substituted divalent oxide which is dependent on the type of housing and stability as previously considered in Section 4.2, beside ionic radius and polarizability of the respective cations. 4.4 Interpretation of Optical Band Gap Energy (Eopt ) and Urbach Energy (E) of the Studied Glasses The values of the optical mobility gap (Eopt ) and the width of the energy (E) thus obtained for all the glasses with 5 % (SrO, BaO and PbO) are given in Table 2 along with the probable error of ±0.005 eV. Eopt and E are observed to be maximum for the base bismuth silicate glasses for both before and after gamma irradiation. The variation of optical band gap energies for these glasses reveals an observed decrease with decrease of the Bi2 O3 content. A possible explanation for this behavior is the change in network structure with the addition of SrO, BaO and PbO replacing Bi2 O3 . Before irradiation it can be seen from Fig. 5 that the values of Eopt are higher than after gamma irradiation (Fig. 6). This can be understood in terms of the structural changes that are taking place in the glass system. The addition of either SrO, BaO or PbO instead of Bi2 O3 decreases the rate of formation of bismuth octahedra. The introduction of modifier ions with increasing ionic radius is the reason for the open structure which leads to less bonding and consequently a smaller band gap. The higher value of Eopt for PbO containing glass is attributed to the presence of Pb2+ ions in the glassy matrix partly in former linkage giving rise to O–Pb4+ –O–Pb2+ –O–Pb2+ chains. It appears that for every Pb2+ –O–Pb2+ unit there exists one O–Pb4+ –O unit, which being more covalent, not only strengthens the glass network but also increases the number of bridging oxygens [43]. The values of E are found (Table 2) to lie between 0.28 and 0.97 eV for the studied glass samples before and after gamma irradiation. This confirms that the bonding in SrO, BaO and PbO doped glass is different from that of

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the binary bismuth silicate glass due to the increase of nonbridging oxygen. The change of E with divalent oxide can be related to ionic radius and the ability to form additional former groups. The values of Eopt decrease after gamma irradiation which could be explained on the basis that the effect of gamma irradiation is to increase the spin density and thus the density of unpaired electrons in unfilled bands [43]. Also, the band tailing is so pronounced as to result in a decrease in the forbidden energy gap.

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Witkowska et al. [53] have suggested that BiO5 units dominate in all the studied Bi2 O3 –SiO2 glasses within the range (0.3 % – 0.5 % Bi2 O3 ) as evidenced by EXAFS and MD studies. They have further postulated that the SiO coordination number is stable and that the Si atoms have exactly four oxygen neighbors. Simon et al. [54] have studied Bi2 O3 –SiO2 glasses and glass–ceramics by X-ray photoelectron spectroscopy (XPS) and have assumed that the increase of Bi2 O3 results in an increase of the covalence degree of the Bi-O bond, allowing the formation of (BiO5 , BiO6 )n polymeric chains.

4.5 Interpretation of the Infrared Absorption Spectra 4.5.2 Interpretation of the FTIR Results Before interpretation of the FTIR results, it is helpful to introduce a summary of the status of the constitution of binary bismuth silicate glass in relation to IR vibrational bands including the expected main structural units in such specific types of unfamiliar heavy metal oxide glass. 4.5.1 The Constitution of Bismuth Silicate Glass Bi2 O3 is a nontraditional oxide which can combine in high contents with SiO2 , B2 O3 or P2 O5 and form stable glasses like that known for PbO. One of the reasons is that both Bi2 O3 and PbO possess asymmetrical structural units in the network structure and each can possibly form bonds with different lengths in distorted polyhedra. Also, Bi3+ and Pb2+ ions have the same 6s2 electronic configuration. Lead exists mostly in glasses, in the divalent state (Pb2+ ) and is able to form structural forming units such as PbO4 and PbO3 besides also being able to reside in modifying positions. Bismuth is mostly accepted to be present in glasses when melted under atmospheric conditions in the trivalent state (Bi3+ ) and is assumed to be able to form BiO6 , BiO3 , and BiO5 , according to various scientists [39, 44, 45]. The structural role played by Bi2 O3 in glasses is not completely clarified. Early in 1969, Bishay and Maghrabi [46] claimed that BiO3 groups are formed in bismuth borate glasses and that the presence of Bi2 O3 promotes the transformation of some triangular coordinated state of boron (BO3 ) to tetrahedral state (BO4 ). Later, Dimitrev et al. [47, 48] and Feller et al. [49, 50] have indicated that bismuth ions can participate both as network modifiers and as network formers. They have assumed that BiO6 groups are modifiers and BiO3 units are former groups. The six Bi-O bonds in the (BiO6 ) octahedron are assumed [51] to be classified into groups of short Bi-O ˚ and long ones (2.5–2.8 A) ˚ on the basis of bonds (2.0–2.2 A) Bi-O interatomic distances. Miyaji et al. [52] have assumed that the distorted BiO6 octahedron involves BiO3 species, when three Bi-O distances in the BiO6 octahedron are nearly equal.

For the contribution of the infrared absorption spectrum of the studied binary bismuth silicate glass, the following suggestions are introduced to realize and interpret the experimental data: (a) The IR spectral feature shows some resemblance to the spectra usually obtained from commercial glassy and crystalline silicate materials. (b) The main vibrational modes associated with the glass network appear mostly in the range 400–1,400 cm−1 and these modes are due to vibrations of structural network forming groups. (c) The IR modes within the range 2,000–4,000 cm−1 are originating from vibrations of water, hydroxyl and silanol (SiOH) groups. (d) The broad distinct band at 482 cm−1 with three connected peaks at 460, 515 and 560 cm−1 can be related to combined vibrations of bending Si-O-Si together with Bi-O bonds in distorted (BiO6 ) octahedral and also Pb-O as PbO4 upon the introduction of PbO within the glass composition. (e) The small peak at about 680 cm−1 is related to vibrations of the Bi-O bonds in distorted (BiO6 ) polyhedra. (f) The distinct broad band at about 871 cm−1 with its two connected peaks at 740 and 900 cm−1 can be related to the combined vibrations of both Si-O-Si symmetric stretching of bridging oxygens between the tetrahedra together with stretching vibrations of Bi-O bonds in (BiO6 ) octahedra. Some authors [14, 52, 53] have assumed that the IR absorption band in the region (840–880 cm−1 ) is a composite one and can be deconvoluted to two separate peaks, one at 860 cm−1 , due to (BiO6 ) octahedra, and the other at about 847 cm−1 , due to (BiO3 ) groups. They have further assumed that (BiO6 ) polyhedra play the role of glass modifier while the (BiO3 ) polyhedra play the role of network former. (g) The distinct broad band with a peak at 1,095 cm−1 and its subsidiary connected peak at 1,020 cm−1 can be attributed to the Si-O-Si antisymmetric stretching of bridging oxygens within the tetrahedron.

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(h) The rest of the small peaks at 1,407, 1,500, 1,639, 3,799 cm−1 can be related to OH, water and SiOH vibrations [13, 28–30]. (i) The effects of the divalent oxides on the FTIR are variable because SrO and BaO act as modifiers and the main IR vibrational modes are as invariant as the base glass. On the introduction of PbO, the FTIR spectra reveal distinct variations because PbO is known to be able to partly form extra structural units (as PbO4 or PbO3 ) beside the silicate network and the sharing of structural units from Bi-O linkages. The IR spectral range from 400 to 1,100 cm−1 show very sharp bands at 470–481, and 860–865 cm−1 and these sharp bands represent the existence of both vibrations due to Bi-O and Pb-O linkages beside the silicate network [13, 14]. Table 3 gives the detailed FTIR bands and their assignments. 4.5.3 Interpretation of the Effect of Gamma Irradiation on FTIR Spectra Recently, Chanthima et al. [46] have compared the shielding properties of silicate glasses containing Bi2 O3 , PbO and BaO towards radiation through the calculation of the mass attenuation coefficient, effective atomic number, effective electron density, the half-value layer and the theoretical approach. The calculated values have been compared with some standard shielding constants. The results have indicated better shielding properties of these specific glasses containing heavy metal oxides than other borate or cabal glasses without heavy metal oxides [26, 27]. Table 3 Peak positions, assignments and related references Peak position Assignment

References

400–475

[13–16, 40–46, 49]

680 720–980 860–880

460–510

1000–1200

1630–1680 3140–4000

Bi – O and Pb – O vibrations Bi – O bands in (BiO6 ) octahedral Pb – O bands in PbO3 units Bi – O bands in (BiO6 ) octahedral Pb – O bonds in PbO3 Stretching vibrations of Bi – O bonds in (BiO6 ) octahedral or combined BiO6 and BiO3 Silicate network Si – O – Si and O – Si – O bending mode Si – O – Si antisymetric stretching of bridging oxygens within the tetrahedron Molecular water Molecular water, OH or silonal, Hydrogen bonding

[40–46, 49] [13–16, 49, 50] [13–16, 39, 46–48]

[14]

[14]

[3, 14] [3, 14]

Recently, ElBatal et al. [16] have reached the conclusion that gamma ray interactions with bismuth borate glasses doped by 3d transition metal ions cause no obvious variations on the FTIR spectra. They have stressed the fact that the presence of a high percent of heavy Bi3+ cations in glasses promotes shielding effects towards successive gamma irradiation. It can thus be concluded that the structural building units containing heavy metal oxides (Bi2 O3 , SrO, BaO, PbO) are stable and show resistance to gamma irradiation.

5 Conclusion Binary bismuth silicate glass together with samples containing parts of Bi2 O3 substituted by SrO, BaO or PbO were prepared and their optical and FTIR spectra were measured before and after gamma irradiation. Strong UVnear visible bands have been identified from both trace iron impurities and the sharing of Bi3+ ions. Gamma irradiation produced some changes in the intensity of the bands and a shift of the first UV band but did not produce any visible bands. This behavior is related to the shielding behavior of glass containing heavy metal oxide (70 % Bi2 O3 ). The samples containing substituted oxides (SrO, BaO, or PbO) show some variations and also their response to the gamma rays depends on the type of oxide introduced. This may be related to different parameters including the type of housing of the oxide (former or modifier), the ionic radius and the polarizability of the cations. Infrared absorption spectral measurements reveal vibrational bands due to the silicate network together with vibrations due to Bi-O linkages present as BiO6 or BiO3 groups. The glasses containing substituted SrO or BaO show minor variations than the parent base glass due to the presence of SrO and BaO in modifying positions. The glasses containing parts of PbO show distinct IR variations due to the sharing of PbO partly in structural building units and the appearance of strong IR vibrations within the spectral range 400–880 cm−1 . Such a wide spectral range is assumed to contain obvious combined vibrational modes due to Bi-O and Pb-O and these glasses reveal sharp bands. All the studied glasses after gamma irradiation exhibit high shielding behavior and the maintenance of the IR vibrational modes. This result confirms the usefulness of these specific containing high percentages of heavy atomic weight oxides as radiation shielding candidates. The values of E are consistent with the trend of Eopt values. The variations in the values of Eopt and E and g can be understood in terms of the structural changes that are taking place in the glass samples upon changes in the composition of the glass.

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References 1. Williams RT, Friebele EJ (1986) In: Weber MJ (ed) Handbook of laser science and technology, section 2 radiation damage in optically transmitting crystals and glasses. CRC Press Inc, Boca Raton, FL, pp 299–449 2. Lell L, Kreidl NJ, Hensler JR (1966) Radiation effects in quartz, silicate and glasses. In: Burke J (ed) Progress in ceramic science, vol 4. Pergamon Press, Oxford, pp 1–93 3. Bishay A (1970) Radiation induced color centres in multicomponent glasses. J Non-Cryst Solids 3:54–114 4. Friebele EJ (1991) In: Uhlmann DR, Kreidl NJ (eds) Optical properties of glass. American Ceramic Society, Westerville, OH, pp 205–262 5. Seeber W, Ehrt D (1999) Glastech Ber Glass Sci Technol 72:295– 302 6. Natura U, Ehrt D, Neumann K (2001) Glastech Ber Glass Sci Technol 74:23–31 7. Moncke D, Ehrt D (2004) Opt Mater 25:425–437 8. Marzouk SY, Elbatal FH (2006) Nucl Inst Methods Phys Res B 248:90–102 9. ElBatal FH, Azooz MA, Marzouk SY (2006) Phys Chem Glasses Eur J Glass Sci Technol B 47:588–597 10. ElBatal FH, Salem AM, Marzouk SY, Azooz MA (2007) Physica B 398:126–134 11. ElBatal FH, Hamdy YM (2008) Trans Indian Ceramic Soc 67:193–202 12. ElBatal FH, Hamdy YM, Marzouk SY (2010) J Non-Cryst Solids 356:46–55 13. ElBatal FH, Azooz MA, Ezz ElDin FM (2002) Phys Chem Glass 43:260–266 14. ElBatal FH (2007) Nucl Inst Methods Phys Res B 254:243–253 15. ElBatal FH, Marzouk SY, Nada N, Desouky SM (2007) Physica B 391:88–99 16. ElBatal FH, Marzouk MA, Abdelghany AM (2011) J Mater Sci 46:5140–5152 17. Singh H, Singh K, Gerward L, Singh K, Sahota HS, Nathuram R (2003) Nucl Inst Methods Phys Res B 207:257–262 18. Singh N, Singh KJ, Singh K, Singh H (2004) Nucl Inst Methods Phys Res B 225:305–309 19. Singh KJ, Singh N, Kumdal RS, Singh K (2008) Nucl Inst Methods Phys Res 266:944–948 20. Chimalawong P, Kaewkhao J, Limsuwan P (2010) Energy Res J 1(2):176–181 21. Mott N, Davis E (1979) Electronic process in non-crystalline materials, 2nd edn. Clarendon Press, Oxford, p 289 22. Sze SM (2007) Semiconductor devices physics and technology, 3rd edn. Wiley, Canada 23. Urbach F (1953) Phys Rev 92:1324

295 24. Sigel GH, Ginther RJ (1968) Glass Technol 9:66 25. Cook L, Mader KH (1982) J Amer Ceram Soc 65:597–601 26. ElBatal FH, Azooz MA, Marzouk SY, Selim MS (2007) Physica B 398:126 27. ElBatal FH, El Kheshen A, Azooz MA, Abo Naf SM (2008) Opt Mater 30:881–891 28. ElBatal FH, Hamdy YM, Marzouk SY (2009) J Non-Cryst Solids 355:2439 29. ElBatal FH, Azooz MA, ElKheshen AA (2009) Trans Indian Ceram Soc 68(2):81–90 30. ElBatal FH, Marzouk SY, Nada N, Desouky SM (2010) Phil Mag 90(6):675–697 31. Duffy JA, Ingram MD (1974) Phys Chem Glass 15:34 32. Duffy JA (1997) Phys Chem Glass 38:289–292 33. Paul A (1972) Phys Chem Glass 13:14 34. Parke S, Webb RS (1973) J Phys Chem Solids 34:85 35. Reisfeld J, Boehm L (1974) J Non-Cryst Solids 16:83 36. Van Kirk SE, Martin SW (1992) J Amer Ceram Soc 75:1028 37. Feltz A, Morr A (1985) J Non-Cryst Solids 74:313 38. Sanz O, Aro-Ponatwski EH, Gonzzlo J, Fernandez Navarro JM (2006) J Non-Cryst Solids 352(8):761–768 39. ElBatal FH, Marzouk MA, Abdelghany AM (2011) J Mater Sci 46:5140–5152 40. Denker BL, Galagan BI, Shlmap IL, Sverchkov SE, Dianov EM (2011) Appl Phys B 103:681–685 41. Ren J, Yang L, Qiu J, Chen D, Jiang X, Zhu C (2006) Solid State Commun 140:38–41 42. Cotton AF, Wilkinson G, Murillo CA, Bockmann M (1999) Advanced inorganic chemistry, 6th edn. Wiley, New York, NY 43. Abo-Naf SM, Elwan RL, Marzouk MA (2012) J Mater Sci: Mater Electron 23:1022–1030 44. Kirdsiri K, Kaewkhao J, Chanthima N, Limsuwan P (2011) Ann Nucl Energy 38:1438 45. Chanthima N, Kaewkhao J, Limsuwan P (2012) Ann Nucl Energy 41:119 46. Bishay A, Maghrabi C (1969) Phys Chem Glass 10:1 47. Dimitriev Y, Michailova V (1990) J Mater Sci Lett 9:1251 48. Dimitriev Y, Michailova V (1992) Proc XVI Intern Cong on Glass, Madrid 3:293 49. Stehle C, Vira C, Hogan D, Feller S, Affatigato MH (1998) Phys Chem Glas 39:83 50. Stentz D, George HB, Feller SA, Affatigato MA (2000) Phys Chem Glas 41:406 51. Malmros G (1970) Acta Chemica Scand 24:384 52. Miyaji F, Sakka S (1991) J Non-Cryst Solids 143:77 53. Witkowska A, Regficki J, Eicco AD (2003) J Alloys Compd 324:109 54. Simon V, Todea M, Takacs AF, Neumann M, Simon S (2007) Solid State Commun 141:42