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Influence of CuO content on the structure of lithium fluoroborate glasses: Spectral and gamma irradiation studies
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 788–792
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Influence of CuO content on the structure of lithium fluoroborate glasses: Spectral and gamma irradiation studies A.M. Abdelghany a,⇑, H.A. ElBatal b, F.M. EzzElDin c a
Spectroscopy Department, Physics Division, National Research Center, Dokki, 12311 Cairo, Egypt Glass Department, National Research Center, Dokki, 12311 Cairo, Egypt c National Center for Radiation Research and Technology, Nasr City, Cairo, Egypt b
h i g h l i g h t s
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New base lithium fluoroborate glass Absorbance (Normalized Scale)
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and glasses doped with different content of CuO were prepared. FTIR and UV–vis absorption measured before and after gamma irradiation. UV optical data reveals some different changes that are related to copper ions and irradiation. FTIR spectra show minor variations on the combined vibrational units which are discussed.
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Article history: Received 14 November 2014 Received in revised form 23 February 2015 Accepted 29 April 2015 Available online 8 May 2015 Keywords: Fluoroborate glass Optical properties Infrared absorption spectra Gamma irradiation
a b s t r a c t Glasses of lithium fluoroborate of the composition LiF 15%–B2O3 85% with increasing CuO as added dopant were prepared and characterized by combined optical and FTIR spectroscopy before and after gamma irradiation. The optical spectrum of the undoped glass reveals strong UV absorption with two distinct peaks at about 235 and 310 nm and with no visible bands. This strong UV absorption is related to the presence of unavoidable trace iron impurity (Fe3+) within the materials used for the preparation of this glass. After irradiation, the spectrum of the undoped glass shows a decrease of the intensity of the UV bands together with the resolution of an induced visible broad band centered at about 520 nm. The CuO doped glasses reveal the same UV absorption beside a very broad visible band centered at 780 nm and this band shows extension and splitting to several component peaks with higher CuO contents. Upon gamma irradiation, the spectra of all CuO-doped glasses reveal pronounced decrease of their intensities. The response of irradiation on the studied glasses is correlated with suggested photochemical reactions together with some shielding effect of the copper ions. The observed visible band is related to the presence of copper as distorted octahedral Cu2+ ions. Infrared absorption spectra of the prepared glasses show repetitive characteristic triangular and tetrahedral borate units similar to that published from alkali or alkaline earth oxides B2O3 glasses. A suggested formation of (BO3/2F) tetrahedral units is advanced through action of LiF on B2O3 and these suggested units showing the same position and number as BO4 tetrahedra. Ó 2015 Elsevier B.V. All rights reserved.
Introduction ⇑ Corresponding author. Tel.: +20 1221133152; fax: +20 233370931. E-mail address: [email protected] (A.M. Abdelghany). http://dx.doi.org/10.1016/j.saa.2015.04.105 1386-1425/Ó 2015 Elsevier B.V. All rights reserved.
Borate glass is one of the commonest and easiest glass-forming systems because it possesses peculiar and interesting physical
789
A.M. Abdelghany et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 788–792
Experimental details Preparation of the glasses Samples of nominal composition (85B2O315LiF) wt% and same samples of CuO-doped lithium fluoroborate glasses where copper added as additive (0.5, 1, 2.5 and 5 gm/batch) were prepared in the present study. Reagent laboratory grade H3BO3 (99% from Nasr Lab., Egypt, Fe 10 ppm), LiF (99.0% Fluka, Germany, Fe 0.01%) and CuO (99.0% BDH, England, Fe 0.05%) were used as raw materials. In platinum crucibles, the weighed batches were melted at 1100 °C for 1 h using an electric furnace under normal air atmospheric condition. The crucibles were rotated at intervals to reach acceptable mixing and homogeneity. The melts were poured into warmed stainless steel molds and the prepared samples were transferred to a muffle furnace regulated at 380 °C for annealing. After 1 h, the muffle was switched off and left to cool to room temperature at 30 °C/h.
spectrophotometer (type Jasco corp. V-570 Rel-00 Japan) covering the range from 200 to 1100 nm. FT infrared absorption spectra of the prepared glasses were measured at room temperature in the wavenumber range 4000– 400 cm 1 by a Fourier transform computerized infrared spectrometer type (Nicolet i10). The prepared glasses were mixed in the ratio 1:100 mg glass powder:KBr, respectively. The weighed mixtures were then subjected to a pressure of 5 tons/cm2 to produce clear homogenous discs. The FTIR spectra were measured immediately after preparing the discs then after the samples were irradiated. A 60Co gamma cell (2000 Ci) was used as a 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 gamma dose every successive time. Using a Fricke dosimeter, the absorbed dose in water was measured, rather than in terms of dose in glass. No cavity theory correction was made. Each glass was subjected to a dose of 8 Mrad (=8 104 Gy).
Results Optical absorption of the prepared glasses UV–vis absorption spectra of undoped lithium fluoroborate glass before and after irradiation Fig. 1 illustrates the optical spectra of the undoped glass before and after gamma irradiation. Before irradiation, the spectrum reveals strong charge transfer UV absorption with two distinct bands at 235 and 310 nm and with no visible bands. Upon irradiation, the UV absorption decreases in intensity and with a shift of the second band to 320 nm together with appearance of an induced broad visible band centered at 520 nm.
Optical absorption spectra of CuO-doped glass Fig. 2 shows the optical absorption of the studied glasses doped with additional CuO (0.5–5.0%). All the spectral curves before irradiation reveal the strong UV absorption as the undoped sample beside the appearance of a broad visible-near IR band extending from about 500 to beyond 1100 nm and centered at about 780 nm and with high CuO content samples the broad band is splitted to several component peaks. With gamma irradiation the irradiated samples spectral curves show lower intensities than before irradiation but become closer with the increase of the CuO content.
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properties involving the dual occurrence of triangularly and tetrahedrally coordinated borons. The so-called boron anomaly leads to rich in boron glass chemistry in spite of controversial views regarding this behavior [1–3]. Glasses containing B2O3 find extensive applications including: gamma ray shielding [4], reversible electrodes [5], textile or continuous filament fiber glass [6], inhibiting bacterial growth [7], immobilization of radioactive wastes [8], and recently as biomaterials [9,10]. Glasses containing transition metal ions (TM) exhibit valuable spectroscopic and electrical properties [11,12]. Copper as one of the 3d TMs imparts greenish and bluish colors to some filter glasses beside the red glass hematite, aventurine and rubies where a combination of Cu2+, Cu+ and metallic copper Cu0 are existing together [13,14]. The stability of both the two oxidation states Cu+ and Cu2+ ions is very sensitive to environment [11,13,14]. In glass, it is known that the valence state of copper affects not only chemical and physical properties but also the glass-forming ability [15]. Extensive recent optical and infrared absorption spectral studies on various phosphate, silicate and borate glasses containing varying CuO as dopant have been carried out before and after gamma irradiation [16–21]. Optical absorption spectra of different glasses reveal a characteristic broad band at 780–880 nm due to distorted octahedral Cu2+ ions which on high concentration of CuO shows splitting to several component extended peaks. Also, it has been reached that copper ions show some shielding behavior toward gamma irradiation which are more initiated by the collective presence of heavy metal oxides such as PbO or Bi2O3 [16,19,21]. The present work aims to study the state of copper ions in lithium fluoroborate host glass and before and after gamma irradiation. The optical spectra of the prepared undoped fluoroborate glass and also derived glasses with additional varying content doped CuO-glasses were examined by collective UV/vis spectral measurements before and after gamma irradiation to justify the state of copper ions. The network structural building units of the studied glass system was determined by FTIR spectral analysis to elucidate the detailed structural groups and the role of both CuO and gamma irradiation.
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Property measurements Optical (UV/vis) absorption spectra were measured for perfectly polished glass samples of equal thickness (2 mm ± 0.1 mm) before and after gamma irradiation using a recording double beam
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Wavelength (nm) Fig. 1. Optical spectra of the undoped glass before and after gamma irradiation.
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Fig. 2. Optical absorption of the studied glasses doped with CuO (0.5–5.0%).
Infrared absorption spectra of the studied glasses
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Fig. 3a illustrates the FTIR spectra of the undoped and CuO-doped lithium fluoroborate glasses. The IR spectral characteristics of the undoped LiF–B2O3 glass reveal the following spectral features:
The glasses containing increasing additives CuO dopant concentrations reveal some changes in their IR spectra which are summarized as follows:
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(1) The intensity of all the main characteristic bands decreases and this decrease is more pronounced in the peaks at 465 and 545 cm 1. (2) The first broad band becomes broader extending from about 800 to about 1200 cm 1. (3) The second broad band extends from about 1200 to 1600 cm 1 and remains higher in intensity than the first broad band.
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(a) An intense far IR broad band is identified with four distinct sharp peaks at 403, 436, 473 and 508 cm 1. (b) A second medium and sharp band at 676 cm 1 is identified. (c) A first broad mid-IR and strong band with two distinct peaks at 936 and 1035 cm 1 is observed. (d) A second mid IR very broad and strong band with five peaks at 1252, 1341, 1384, 1422, and 1627 cm 1 is identified. (e) Two small consecutive bands are identified at 2854 and 2923 cm 1. (f) A broad near IR band is centered at 3436 cm 1.
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Fig. 3b shows the deconvoluted FTIR spectra of sample that contains 2.5 gm/batch CuO. The spectra are used to identify the vibrational bands related to the suggested network groups of the glass constituents.
A.M. Abdelghany et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 788–792
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Discussion Interpretation of the origin of the strong UV absorption in the studied undoped and CuO doped glasses Sigel and Ginther [22] and Cook and Mader [23] have separately identified strong ultraviolet absorption bands in various undoped commercial glasses. They have attributed that such strong UV absorption originated from unavoidable trace iron (Fe3+ ions) present as impurities within the raw materials used for the preparation of these commercial glasses. Duffy and Ingram [24] and Duffy [25] have classified various UV absorption in glasses. They have referred to the ability of some transition metal ions (e.g. Fe3+, Cr6+ . . ..) to exhibit distinct strong UV absorption bands in glasses even if present in the ppm level. Such specific metal ions owe their characteristic UV absorption to an electron transfer mechanism. Ehrt et al. [26–28] have reached to the same assumptions regarding the ability of trace iron impurities to cause deterioration of the UV transmission in optical phosphate and borosilicate glasses. They have claimed for the need for ultrapure chemicals for the preparation of special optical glasses for recent applications. Recently ElBatal et al. [16–21], have confirmed the appearance of strong UV absorption bands in various undoped borate, phosphate and silicate glasses and they have related such UV bands to the presence of trace iron impurities (Fe3+ ions) contaminated within the materials used for the preparation of such collective glasses. It can thus suggested that the observed UV bands from the undoped lithium fluoroborate glass are due to trace iron (Fe3+ ions) present as impurities within the chemicals used for preparation and this specific UV bands which are extended and observed within the spectra of CuO doped glasses. Interpretation of the optical spectra of CuO-doped glasses Spectral and color data reveal two new major characteristics, the green bluish color for the samples together with the appearance of a very broad band extending from 500 to 1200 nm and centered at about 780 nm. These properties indicate the presence of copper ions in the divalent state as (Cu2+) ions. This divalent state of copper is the only known ion having the 3d5 configuration [11,29]. The energy diagram for d5 system in octahedral symmetry is just the inverse of that for octahedral d1 system revealing a single visible band [11,29].
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Fig. 2 shows within the optical spectra of the CuO-doped samples the same strong UV absorption bands previously identified in the spectrum of the undoped glass. The same reasoning can be applied through relating these UV bands to trace Fe3+ ions present as impurities within the chemicals. Numerous glass scientists have advanced different views regarding the interpretation of the visible absorption due to divalent copper even though one is dealing with an ion with the equivalent of one electron case [15–21,30]. Paul [29] has assumed that a close study of the asymmetric band around 800 nm in a variety of complexes shows that this band is virtually made up of at least two, and possibly three or four overlapping symmetric bands [31]. The present optical spectra of high CuO-doped glasses reveal several splitted peaks within the entire range of the broad band due to Cu2+ ions, and their behavior supports the previous assumption. Duran et al. [13] have assumed that in Cu2+ chemistry there is no crystallographic evidence for a static regular octahedral stereochemistry whose lack of symmetry caused by an electronic hole in the dx2 y2 orbital produces the tetragonal distortion known as the Jahn–Teller effect. They have assumed that three absorption peaks due to the transitions 2B1g ? 2B2g, 2B1g ? 2A1g and 2B1g ? 2Eg can appear in the visible and near-infrared region. They further added that the increasing distortion with change in the chemical composition may be related to the change of the polarizability of the oxygen ion surrounding the Cu2+ ions, and to the dependence on the field strength of the network former and modifier ions. Based on previous postulations, the broad visible/near IR peaks are correlated with divalent Cu2+ ions in octahedral symmetry with distinct distortion and the broadness and asymmetry of these bands are assumed to be due to splitting of a low symmetry ligand field component [32,33].
Interpretation of the effect of gamma irradiation on the optical spectra of the studied glasses It is accepted that the effects of ionizing radiations (c-rays, UV radiation) on glasses depend on the type of glass and its chemical constituents, the intrinsic defects already present within the glass (nonbridging oxygens, oxygen vacancies, or flaws created by the high energy generated electrons) and the dose of irradiation [34,35]. The undoped glass shows a decrease in the intensity of the UV absorption and the resolution of an induced visible band upon irradiation. The decrease of the UV absorption can be explained by assuming photochemical reactions between Fe3+ ions and generated positive holes during irradiation and the formation of Fe2+ ions which are known to have their main absorption at about 1100 nm and therefore the absorption due to Fe3+ ions in the UV region is observed to decrease. The resolution of an induced visible/near infrared band can be related to the effect of irradiation on the base glass itself and the formation of nonbridging oxygen hole center (NBOHC) or boron oxygen hole center (BOHC) as suggested by Bishay [34] and Friebele [35].
Interpretation of the FT infrared spectra Fig. 3 illustrates the FTIR spectra of the studied glasses and the inspection of the IR vibrational bands indicate the resemblance of these bands to that published from various alkali and alkaline earth oxides borate glasses [3]. Based on such close similarity, the FTIR results can be interpreted on the following basis:
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(a) The close similarity of the number and position of the main vibrational bands due to BO3 and BO3F groups in the present studied (LiFB2O3) glass to various published IR spectra of Li2O–B2O3 glass as pointed out by many authors [3,36–38] can be ascribed to the sharing the boron element itself. The boron element is the highest or smallest mass capable to form glass with the sharing of oxygen. (b) It is therefore expected that the main vibrational modes associated with the borate network appear well above 500 cm 1 in the mid-infrared region. (c) The vibrational modes due to BO3 and BO4 (or BO3F) groups are well separated from the vibrational modes due to metal ions sites which are active in the far-infrared region i.e. below 600 cm 1. (d) The support of the assumption that boron plays a main role for the observed IR results comes from the formation of both triangular and tetrahedral units within the same position of BO3 and BO4 groups. (e) The absorption peaks in the region of about 1200– 1600 cm 1 are attributed to stretches of B-O in BO3 or (BO2O-) units as suggested by several authors [3,9,10,39] originating from the introduced B2O3 main glass constituent. (f) The absorption peaks identified in the region of about 800– 1200 cm 1 is normally related to B-O bond stretching vibrations of BO4 tetrahedra in alkali or alkaline earth oxides borate glasses. There is no alkali oxide in the present studied glasses and several glass scientists [36–38] have suggested that B2O3 is partly modified with alkali or alkaline earth halide. They have suggested that structural units of (BO3/2F)- distorted tetrahedral are the most probably formed units. This assumption is applied to our studied glasses. (g) The absorption peak in the region 670–690 cm 1 is assumed to be due to bending mode vibrations of various borate units. (h) The absorption peaks in the region 400–550 cm 1 can be related to vibrations of metal ions in their modifying sites (e.g. Li+ in our glass) as suggested by various authors [18– 21,39]. (i) The rest of the near IR spectrum shows a broad band centered at about 3400 cm 1 correlated to the molecular water or BOH vibrations [3,10,36]. Conclusion Optical spectrum of undoped lithium fluoroborate glass reveals two strong broad UV absorption bands at 235 and 310 nm but with no visible bands. Such strong UV bands are related to unavoidable trace iron (Fe3+) ions present as impurities within the chemicals used for preparation of this glass. CuO-doped glasses show an extra very broad band centered at 780 nm and in high CuO content glasses reveal splitting to several component peaks. Gamma irradiation decreases the intensity of the UV absorption accompanied with the resolution of an induced visible band at 520 nm. This response to radiation is related to suggested photochemical reaction through librated electrons and positive holes and the formation of induced boron oxygen hole centers or nonbridging oxygen hole centers in the visible region. Gamma irradiation of CuO-doped glasses shows only the decrease of the intensities of spectral curves indicating the suggestion of shielding effect of copper ions.
Infrared absorption spectral curves are repetitive indicating the presence of triangular and tetrahedral borate groups vibrating in their distinct characteristic wavenumbers. It is suggested that (BO3/2F) tetrahedral groups are formed through the reaction of LiF with B2O3 revealing the same vibrational position and extension as BO4 groups. Gamma irradiation shows nearly the same IR spectral features with the assumption of shielding of copper ions. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2015.04.105. References [1] L.D. Pye, V.D. Frechette, N.J. Kreidl (Eds.), Borate Glass: Structure, Properties and Applications, Plenum Press, New York, 1978. [2] A.C. Wright, S.A. Feller, A.C. Hanon (Eds.), Proc. Intern. Conf. Borate Glasses, Crystals and Melts, Society of Glass technology, Sheffield, UK (1997). [3] E.I. Kamitsos, Phys. Chem. Glasses 44 (2003) 79. [4] N. Singh, K.J. Singh, K. Singh, H. Singh, Nucl. Instrum. Methods Phys. Res. B 275 (2009) 305. [5] M. Tutsumisago, A. Hayashi, Glass Technol.: Eur. J. Glass Sci. Technol. A 48 (1) (2006) 6–12. [6] K.L. Loewenstein, The Manufacturing Technology of Continuous Glass Fibers, Glass Science and Technology, 3rd ed., Elsevier, Amesterdam, 1993. [7] D. Lippley, B.A. Melhus, M.R. Leonards, S.A. Feller, M.A. Affatigato, Glass Technol.: Eur. J. Glass Sci. Technol. A 47 (5) (2006) 127. [8] F.M. EzzElDin, Nucl. Instrum. Methods Phys. Res. B 183 (2001) 285–300. [9] M.A. Ouis, A.M. Abdelghany, H.A. ElBatal, Process. Appl. Ceram. 6 (3) (2012) 141–149. [10] A.M. Abdelghany, H.A. ElBatal, F.M. EzzElDin, Ceram. Int. 38 (2012) 1105– 1113. [11] C.R. Bamford, Colour Generation and Control in Glass, Elsevier Science Publisher, Amsterdam, 1977. [12] N.F. Mott, J. Non-Cryst. Solids 1 (1968) 1. [13] A. Duran, J.R. Jurado, J.M.F. Navarro, J. Non-Cryst. Solids 79 (1986) 333. [14] E. Metwalli, J. Non-Cryst. Solids 317 (2003) 221–230. [15] B.S. Bae, M.C. Weinberg, J. Am. Ceram. Soc. 76 (1993) 1395. [16] F.H. ElBatal, S.Y. Marzouk, N. Nada, S.M. Desouky, Physica B 391 (2007) 88. [17] F.H. ElBatal, J. Mater. Sci. 43 (2008) 1070. [18] H.A. ElBatal, Z. Mandouh, H. Zayed, S.Y. Marzouk, G. Elkomy, A. Hosny, Physica B 405 (2010) 4755. [19] N.A. Ghoneim, H.A. ElBatal, A.M. Abdelghany, I.S. Ali, J. Alloys Compd. 509 (2011) 6913. [20] H.A. ElBatal, A.M. Abdelghany, F.H. ElBatal, Kh.M. ElBadry, F.A. Moustaffa, Physica B 406 (2011) 3694. [21] H.A. ElBatal, A.M. Abdelghany, I.S. Ali, J. Non-Cryst. Solids 358 (2012) 820–825. [22] G.H. Sigel Jr., J.R. Ginther, Glass Technol. 9 (1968) 99. [23] L. Cook, K.H. Mader, J. Am. Ceram. Soc. 65 (1982) 609. [24] J.A. Duffy, M.D. Ingram, Phys. Chem. Glass 15 (1974) 34. [25] J.A. Duffy, Phys. Chem. Glasses 38 (1997) 289. [26] W. Seeber, D. Ehrt, Glastech. Ber. Glass Sci. Technol. 70 (1997) 312. [27] U. Natura, D. Ehrt, Glastech. Ber. Glass Sci. Technol. 72 (1995) 295. [28] D. Monke, D. Ehrt, Opt. Mater. 25 (2004) 425. [29] A. Paul, Chemistry of Glass, 2nd ed., Chapman and Hall, New York, 1990. [30] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic Chemistry, 6th ed., John Wiley-Intersience, New York, 1999. [31] A.G. Tomlinson, B.T. Hathaway, D. Billing, R. Nicols, J. Chem. Soc. A 65 (1969). [32] R.V.N. Ravikumar, A.V. Chandrasekhar, J. Ramoorthy, R.J. Reddy, T. Yamouchi, P.S. Rao, J. Alloys Compd. 364 (2004) 176. [33] V. Kamalaker, G. Upender, M. Prasad, V. Chandra Mouli, Indian J. Pure Appl. Phys. 48 (10) (2010) 709–715. [34] A. Bishay, J. Non-Cryst. Solids 3 (1970) 54. [35] E.J. Friebele, in: Optical Properties of Glass, (Eds.) D.R. Uhlmann, N.J. Kreidl, American Ceramic Society, Westerville, OH, USA (1991)pp209-262. [36] J.E. Shelby, L.D. Baker, Phys. Chem. Glasses 39 (1) (1998) 23. [37] I.Z. Hager, M. El-Hofy, Phys. Status Solidi A 198 (2003) 7. [38] H. Doweidar, G. ElDamrawi, M. Abdelghany, J. Mater. Sci. 47 (2012) 4028. [39] F.H. Elbatal, A.A. Elkheshen, M.A. Azooz, S.M. Abou Naf, Opt. Mater. 30 (2008) 881.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Influence of CuO content on the structure of lithium fluoroborate glasses: Spectral and gamma irradiation studies A.M. Abdelghany a,⇑, H.A. ElBatal b, F.M. EzzElDin c a
Spectroscopy Department, Physics Division, National Research Center, Dokki, 12311 Cairo, Egypt Glass Department, National Research Center, Dokki, 12311 Cairo, Egypt c National Center for Radiation Research and Technology, Nasr City, Cairo, Egypt b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
New base lithium fluoroborate glass Absorbance (Normalized Scale)
1.0
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and glasses doped with different content of CuO were prepared. FTIR and UV–vis absorption measured before and after gamma irradiation. UV optical data reveals some different changes that are related to copper ions and irradiation. FTIR spectra show minor variations on the combined vibrational units which are discussed.
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Article history: Received 14 November 2014 Received in revised form 23 February 2015 Accepted 29 April 2015 Available online 8 May 2015 Keywords: Fluoroborate glass Optical properties Infrared absorption spectra Gamma irradiation
a b s t r a c t Glasses of lithium fluoroborate of the composition LiF 15%–B2O3 85% with increasing CuO as added dopant were prepared and characterized by combined optical and FTIR spectroscopy before and after gamma irradiation. The optical spectrum of the undoped glass reveals strong UV absorption with two distinct peaks at about 235 and 310 nm and with no visible bands. This strong UV absorption is related to the presence of unavoidable trace iron impurity (Fe3+) within the materials used for the preparation of this glass. After irradiation, the spectrum of the undoped glass shows a decrease of the intensity of the UV bands together with the resolution of an induced visible broad band centered at about 520 nm. The CuO doped glasses reveal the same UV absorption beside a very broad visible band centered at 780 nm and this band shows extension and splitting to several component peaks with higher CuO contents. Upon gamma irradiation, the spectra of all CuO-doped glasses reveal pronounced decrease of their intensities. The response of irradiation on the studied glasses is correlated with suggested photochemical reactions together with some shielding effect of the copper ions. The observed visible band is related to the presence of copper as distorted octahedral Cu2+ ions. Infrared absorption spectra of the prepared glasses show repetitive characteristic triangular and tetrahedral borate units similar to that published from alkali or alkaline earth oxides B2O3 glasses. A suggested formation of (BO3/2F) tetrahedral units is advanced through action of LiF on B2O3 and these suggested units showing the same position and number as BO4 tetrahedra. Ó 2015 Elsevier B.V. All rights reserved.
Introduction ⇑ Corresponding author. Tel.: +20 1221133152; fax: +20 233370931. E-mail address: [email protected] (A.M. Abdelghany). http://dx.doi.org/10.1016/j.saa.2015.04.105 1386-1425/Ó 2015 Elsevier B.V. All rights reserved.
Borate glass is one of the commonest and easiest glass-forming systems because it possesses peculiar and interesting physical
789
A.M. Abdelghany et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 788–792
Experimental details Preparation of the glasses Samples of nominal composition (85B2O315LiF) wt% and same samples of CuO-doped lithium fluoroborate glasses where copper added as additive (0.5, 1, 2.5 and 5 gm/batch) were prepared in the present study. Reagent laboratory grade H3BO3 (99% from Nasr Lab., Egypt, Fe 10 ppm), LiF (99.0% Fluka, Germany, Fe 0.01%) and CuO (99.0% BDH, England, Fe 0.05%) were used as raw materials. In platinum crucibles, the weighed batches were melted at 1100 °C for 1 h using an electric furnace under normal air atmospheric condition. The crucibles were rotated at intervals to reach acceptable mixing and homogeneity. The melts were poured into warmed stainless steel molds and the prepared samples were transferred to a muffle furnace regulated at 380 °C for annealing. After 1 h, the muffle was switched off and left to cool to room temperature at 30 °C/h.
spectrophotometer (type Jasco corp. V-570 Rel-00 Japan) covering the range from 200 to 1100 nm. FT infrared absorption spectra of the prepared glasses were measured at room temperature in the wavenumber range 4000– 400 cm 1 by a Fourier transform computerized infrared spectrometer type (Nicolet i10). The prepared glasses were mixed in the ratio 1:100 mg glass powder:KBr, respectively. The weighed mixtures were then subjected to a pressure of 5 tons/cm2 to produce clear homogenous discs. The FTIR spectra were measured immediately after preparing the discs then after the samples were irradiated. A 60Co gamma cell (2000 Ci) was used as a 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 gamma dose every successive time. Using a Fricke dosimeter, the absorbed dose in water was measured, rather than in terms of dose in glass. No cavity theory correction was made. Each glass was subjected to a dose of 8 Mrad (=8 104 Gy).
Results Optical absorption of the prepared glasses UV–vis absorption spectra of undoped lithium fluoroborate glass before and after irradiation Fig. 1 illustrates the optical spectra of the undoped glass before and after gamma irradiation. Before irradiation, the spectrum reveals strong charge transfer UV absorption with two distinct bands at 235 and 310 nm and with no visible bands. Upon irradiation, the UV absorption decreases in intensity and with a shift of the second band to 320 nm together with appearance of an induced broad visible band centered at 520 nm.
Optical absorption spectra of CuO-doped glass Fig. 2 shows the optical absorption of the studied glasses doped with additional CuO (0.5–5.0%). All the spectral curves before irradiation reveal the strong UV absorption as the undoped sample beside the appearance of a broad visible-near IR band extending from about 500 to beyond 1100 nm and centered at about 780 nm and with high CuO content samples the broad band is splitted to several component peaks. With gamma irradiation the irradiated samples spectral curves show lower intensities than before irradiation but become closer with the increase of the CuO content.
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properties involving the dual occurrence of triangularly and tetrahedrally coordinated borons. The so-called boron anomaly leads to rich in boron glass chemistry in spite of controversial views regarding this behavior [1–3]. Glasses containing B2O3 find extensive applications including: gamma ray shielding [4], reversible electrodes [5], textile or continuous filament fiber glass [6], inhibiting bacterial growth [7], immobilization of radioactive wastes [8], and recently as biomaterials [9,10]. Glasses containing transition metal ions (TM) exhibit valuable spectroscopic and electrical properties [11,12]. Copper as one of the 3d TMs imparts greenish and bluish colors to some filter glasses beside the red glass hematite, aventurine and rubies where a combination of Cu2+, Cu+ and metallic copper Cu0 are existing together [13,14]. The stability of both the two oxidation states Cu+ and Cu2+ ions is very sensitive to environment [11,13,14]. In glass, it is known that the valence state of copper affects not only chemical and physical properties but also the glass-forming ability [15]. Extensive recent optical and infrared absorption spectral studies on various phosphate, silicate and borate glasses containing varying CuO as dopant have been carried out before and after gamma irradiation [16–21]. Optical absorption spectra of different glasses reveal a characteristic broad band at 780–880 nm due to distorted octahedral Cu2+ ions which on high concentration of CuO shows splitting to several component extended peaks. Also, it has been reached that copper ions show some shielding behavior toward gamma irradiation which are more initiated by the collective presence of heavy metal oxides such as PbO or Bi2O3 [16,19,21]. The present work aims to study the state of copper ions in lithium fluoroborate host glass and before and after gamma irradiation. The optical spectra of the prepared undoped fluoroborate glass and also derived glasses with additional varying content doped CuO-glasses were examined by collective UV/vis spectral measurements before and after gamma irradiation to justify the state of copper ions. The network structural building units of the studied glass system was determined by FTIR spectral analysis to elucidate the detailed structural groups and the role of both CuO and gamma irradiation.
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Property measurements Optical (UV/vis) absorption spectra were measured for perfectly polished glass samples of equal thickness (2 mm ± 0.1 mm) before and after gamma irradiation using a recording double beam
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Wavelength (nm) Fig. 1. Optical spectra of the undoped glass before and after gamma irradiation.
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Fig. 2. Optical absorption of the studied glasses doped with CuO (0.5–5.0%).
Infrared absorption spectra of the studied glasses
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Fig. 3a illustrates the FTIR spectra of the undoped and CuO-doped lithium fluoroborate glasses. The IR spectral characteristics of the undoped LiF–B2O3 glass reveal the following spectral features:
The glasses containing increasing additives CuO dopant concentrations reveal some changes in their IR spectra which are summarized as follows:
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(1) The intensity of all the main characteristic bands decreases and this decrease is more pronounced in the peaks at 465 and 545 cm 1. (2) The first broad band becomes broader extending from about 800 to about 1200 cm 1. (3) The second broad band extends from about 1200 to 1600 cm 1 and remains higher in intensity than the first broad band.
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(a) An intense far IR broad band is identified with four distinct sharp peaks at 403, 436, 473 and 508 cm 1. (b) A second medium and sharp band at 676 cm 1 is identified. (c) A first broad mid-IR and strong band with two distinct peaks at 936 and 1035 cm 1 is observed. (d) A second mid IR very broad and strong band with five peaks at 1252, 1341, 1384, 1422, and 1627 cm 1 is identified. (e) Two small consecutive bands are identified at 2854 and 2923 cm 1. (f) A broad near IR band is centered at 3436 cm 1.
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Fig. 3b shows the deconvoluted FTIR spectra of sample that contains 2.5 gm/batch CuO. The spectra are used to identify the vibrational bands related to the suggested network groups of the glass constituents.
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Absorbance (Normalized Scale)
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Discussion Interpretation of the origin of the strong UV absorption in the studied undoped and CuO doped glasses Sigel and Ginther [22] and Cook and Mader [23] have separately identified strong ultraviolet absorption bands in various undoped commercial glasses. They have attributed that such strong UV absorption originated from unavoidable trace iron (Fe3+ ions) present as impurities within the raw materials used for the preparation of these commercial glasses. Duffy and Ingram [24] and Duffy [25] have classified various UV absorption in glasses. They have referred to the ability of some transition metal ions (e.g. Fe3+, Cr6+ . . ..) to exhibit distinct strong UV absorption bands in glasses even if present in the ppm level. Such specific metal ions owe their characteristic UV absorption to an electron transfer mechanism. Ehrt et al. [26–28] have reached to the same assumptions regarding the ability of trace iron impurities to cause deterioration of the UV transmission in optical phosphate and borosilicate glasses. They have claimed for the need for ultrapure chemicals for the preparation of special optical glasses for recent applications. Recently ElBatal et al. [16–21], have confirmed the appearance of strong UV absorption bands in various undoped borate, phosphate and silicate glasses and they have related such UV bands to the presence of trace iron impurities (Fe3+ ions) contaminated within the materials used for the preparation of such collective glasses. It can thus suggested that the observed UV bands from the undoped lithium fluoroborate glass are due to trace iron (Fe3+ ions) present as impurities within the chemicals used for preparation and this specific UV bands which are extended and observed within the spectra of CuO doped glasses. Interpretation of the optical spectra of CuO-doped glasses Spectral and color data reveal two new major characteristics, the green bluish color for the samples together with the appearance of a very broad band extending from 500 to 1200 nm and centered at about 780 nm. These properties indicate the presence of copper ions in the divalent state as (Cu2+) ions. This divalent state of copper is the only known ion having the 3d5 configuration [11,29]. The energy diagram for d5 system in octahedral symmetry is just the inverse of that for octahedral d1 system revealing a single visible band [11,29].
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Fig. 2 shows within the optical spectra of the CuO-doped samples the same strong UV absorption bands previously identified in the spectrum of the undoped glass. The same reasoning can be applied through relating these UV bands to trace Fe3+ ions present as impurities within the chemicals. Numerous glass scientists have advanced different views regarding the interpretation of the visible absorption due to divalent copper even though one is dealing with an ion with the equivalent of one electron case [15–21,30]. Paul [29] has assumed that a close study of the asymmetric band around 800 nm in a variety of complexes shows that this band is virtually made up of at least two, and possibly three or four overlapping symmetric bands [31]. The present optical spectra of high CuO-doped glasses reveal several splitted peaks within the entire range of the broad band due to Cu2+ ions, and their behavior supports the previous assumption. Duran et al. [13] have assumed that in Cu2+ chemistry there is no crystallographic evidence for a static regular octahedral stereochemistry whose lack of symmetry caused by an electronic hole in the dx2 y2 orbital produces the tetragonal distortion known as the Jahn–Teller effect. They have assumed that three absorption peaks due to the transitions 2B1g ? 2B2g, 2B1g ? 2A1g and 2B1g ? 2Eg can appear in the visible and near-infrared region. They further added that the increasing distortion with change in the chemical composition may be related to the change of the polarizability of the oxygen ion surrounding the Cu2+ ions, and to the dependence on the field strength of the network former and modifier ions. Based on previous postulations, the broad visible/near IR peaks are correlated with divalent Cu2+ ions in octahedral symmetry with distinct distortion and the broadness and asymmetry of these bands are assumed to be due to splitting of a low symmetry ligand field component [32,33].
Interpretation of the effect of gamma irradiation on the optical spectra of the studied glasses It is accepted that the effects of ionizing radiations (c-rays, UV radiation) on glasses depend on the type of glass and its chemical constituents, the intrinsic defects already present within the glass (nonbridging oxygens, oxygen vacancies, or flaws created by the high energy generated electrons) and the dose of irradiation [34,35]. The undoped glass shows a decrease in the intensity of the UV absorption and the resolution of an induced visible band upon irradiation. The decrease of the UV absorption can be explained by assuming photochemical reactions between Fe3+ ions and generated positive holes during irradiation and the formation of Fe2+ ions which are known to have their main absorption at about 1100 nm and therefore the absorption due to Fe3+ ions in the UV region is observed to decrease. The resolution of an induced visible/near infrared band can be related to the effect of irradiation on the base glass itself and the formation of nonbridging oxygen hole center (NBOHC) or boron oxygen hole center (BOHC) as suggested by Bishay [34] and Friebele [35].
Interpretation of the FT infrared spectra Fig. 3 illustrates the FTIR spectra of the studied glasses and the inspection of the IR vibrational bands indicate the resemblance of these bands to that published from various alkali and alkaline earth oxides borate glasses [3]. Based on such close similarity, the FTIR results can be interpreted on the following basis:
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(a) The close similarity of the number and position of the main vibrational bands due to BO3 and BO3F groups in the present studied (LiFB2O3) glass to various published IR spectra of Li2O–B2O3 glass as pointed out by many authors [3,36–38] can be ascribed to the sharing the boron element itself. The boron element is the highest or smallest mass capable to form glass with the sharing of oxygen. (b) It is therefore expected that the main vibrational modes associated with the borate network appear well above 500 cm 1 in the mid-infrared region. (c) The vibrational modes due to BO3 and BO4 (or BO3F) groups are well separated from the vibrational modes due to metal ions sites which are active in the far-infrared region i.e. below 600 cm 1. (d) The support of the assumption that boron plays a main role for the observed IR results comes from the formation of both triangular and tetrahedral units within the same position of BO3 and BO4 groups. (e) The absorption peaks in the region of about 1200– 1600 cm 1 are attributed to stretches of B-O in BO3 or (BO2O-) units as suggested by several authors [3,9,10,39] originating from the introduced B2O3 main glass constituent. (f) The absorption peaks identified in the region of about 800– 1200 cm 1 is normally related to B-O bond stretching vibrations of BO4 tetrahedra in alkali or alkaline earth oxides borate glasses. There is no alkali oxide in the present studied glasses and several glass scientists [36–38] have suggested that B2O3 is partly modified with alkali or alkaline earth halide. They have suggested that structural units of (BO3/2F)- distorted tetrahedral are the most probably formed units. This assumption is applied to our studied glasses. (g) The absorption peak in the region 670–690 cm 1 is assumed to be due to bending mode vibrations of various borate units. (h) The absorption peaks in the region 400–550 cm 1 can be related to vibrations of metal ions in their modifying sites (e.g. Li+ in our glass) as suggested by various authors [18– 21,39]. (i) The rest of the near IR spectrum shows a broad band centered at about 3400 cm 1 correlated to the molecular water or BOH vibrations [3,10,36]. Conclusion Optical spectrum of undoped lithium fluoroborate glass reveals two strong broad UV absorption bands at 235 and 310 nm but with no visible bands. Such strong UV bands are related to unavoidable trace iron (Fe3+) ions present as impurities within the chemicals used for preparation of this glass. CuO-doped glasses show an extra very broad band centered at 780 nm and in high CuO content glasses reveal splitting to several component peaks. Gamma irradiation decreases the intensity of the UV absorption accompanied with the resolution of an induced visible band at 520 nm. This response to radiation is related to suggested photochemical reaction through librated electrons and positive holes and the formation of induced boron oxygen hole centers or nonbridging oxygen hole centers in the visible region. Gamma irradiation of CuO-doped glasses shows only the decrease of the intensities of spectral curves indicating the suggestion of shielding effect of copper ions.
Infrared absorption spectral curves are repetitive indicating the presence of triangular and tetrahedral borate groups vibrating in their distinct characteristic wavenumbers. It is suggested that (BO3/2F) tetrahedral groups are formed through the reaction of LiF with B2O3 revealing the same vibrational position and extension as BO4 groups. Gamma irradiation shows nearly the same IR spectral features with the assumption of shielding of copper ions. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2015.04.105. References [1] L.D. Pye, V.D. Frechette, N.J. Kreidl (Eds.), Borate Glass: Structure, Properties and Applications, Plenum Press, New York, 1978. [2] A.C. Wright, S.A. Feller, A.C. Hanon (Eds.), Proc. Intern. Conf. Borate Glasses, Crystals and Melts, Society of Glass technology, Sheffield, UK (1997). [3] E.I. Kamitsos, Phys. Chem. Glasses 44 (2003) 79. [4] N. Singh, K.J. Singh, K. Singh, H. Singh, Nucl. Instrum. Methods Phys. Res. B 275 (2009) 305. [5] M. Tutsumisago, A. Hayashi, Glass Technol.: Eur. J. Glass Sci. Technol. A 48 (1) (2006) 6–12. [6] K.L. Loewenstein, The Manufacturing Technology of Continuous Glass Fibers, Glass Science and Technology, 3rd ed., Elsevier, Amesterdam, 1993. [7] D. Lippley, B.A. Melhus, M.R. Leonards, S.A. Feller, M.A. Affatigato, Glass Technol.: Eur. J. Glass Sci. Technol. A 47 (5) (2006) 127. [8] F.M. EzzElDin, Nucl. Instrum. Methods Phys. Res. B 183 (2001) 285–300. [9] M.A. Ouis, A.M. Abdelghany, H.A. ElBatal, Process. Appl. Ceram. 6 (3) (2012) 141–149. [10] A.M. Abdelghany, H.A. ElBatal, F.M. EzzElDin, Ceram. Int. 38 (2012) 1105– 1113. [11] C.R. Bamford, Colour Generation and Control in Glass, Elsevier Science Publisher, Amsterdam, 1977. [12] N.F. Mott, J. Non-Cryst. Solids 1 (1968) 1. [13] A. Duran, J.R. Jurado, J.M.F. Navarro, J. Non-Cryst. Solids 79 (1986) 333. [14] E. Metwalli, J. Non-Cryst. Solids 317 (2003) 221–230. [15] B.S. Bae, M.C. Weinberg, J. Am. Ceram. Soc. 76 (1993) 1395. [16] F.H. ElBatal, S.Y. Marzouk, N. Nada, S.M. Desouky, Physica B 391 (2007) 88. [17] F.H. ElBatal, J. Mater. Sci. 43 (2008) 1070. [18] H.A. ElBatal, Z. Mandouh, H. Zayed, S.Y. Marzouk, G. Elkomy, A. Hosny, Physica B 405 (2010) 4755. [19] N.A. Ghoneim, H.A. ElBatal, A.M. Abdelghany, I.S. Ali, J. Alloys Compd. 509 (2011) 6913. [20] H.A. ElBatal, A.M. Abdelghany, F.H. ElBatal, Kh.M. ElBadry, F.A. Moustaffa, Physica B 406 (2011) 3694. [21] H.A. ElBatal, A.M. Abdelghany, I.S. Ali, J. Non-Cryst. Solids 358 (2012) 820–825. [22] G.H. Sigel Jr., J.R. Ginther, Glass Technol. 9 (1968) 99. [23] L. Cook, K.H. Mader, J. Am. Ceram. Soc. 65 (1982) 609. [24] J.A. Duffy, M.D. Ingram, Phys. Chem. Glass 15 (1974) 34. [25] J.A. Duffy, Phys. Chem. Glasses 38 (1997) 289. [26] W. Seeber, D. Ehrt, Glastech. Ber. Glass Sci. Technol. 70 (1997) 312. [27] U. Natura, D. Ehrt, Glastech. Ber. Glass Sci. Technol. 72 (1995) 295. [28] D. Monke, D. Ehrt, Opt. Mater. 25 (2004) 425. [29] A. Paul, Chemistry of Glass, 2nd ed., Chapman and Hall, New York, 1990. [30] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic Chemistry, 6th ed., John Wiley-Intersience, New York, 1999. [31] A.G. Tomlinson, B.T. Hathaway, D. Billing, R. Nicols, J. Chem. Soc. A 65 (1969). [32] R.V.N. Ravikumar, A.V. Chandrasekhar, J. Ramoorthy, R.J. Reddy, T. Yamouchi, P.S. Rao, J. Alloys Compd. 364 (2004) 176. [33] V. Kamalaker, G. Upender, M. Prasad, V. Chandra Mouli, Indian J. Pure Appl. Phys. 48 (10) (2010) 709–715. [34] A. Bishay, J. Non-Cryst. Solids 3 (1970) 54. [35] E.J. Friebele, in: Optical Properties of Glass, (Eds.) D.R. Uhlmann, N.J. Kreidl, American Ceramic Society, Westerville, OH, USA (1991)pp209-262. [36] J.E. Shelby, L.D. Baker, Phys. Chem. Glasses 39 (1) (1998) 23. [37] I.Z. Hager, M. El-Hofy, Phys. Status Solidi A 198 (2003) 7. [38] H. Doweidar, G. ElDamrawi, M. Abdelghany, J. Mater. Sci. 47 (2012) 4028. [39] F.H. Elbatal, A.A. Elkheshen, M.A. Azooz, S.M. Abou Naf, Opt. Mater. 30 (2008) 881.