Trace Iron Impurities Research Articles

Photoluminescence, optical and structural properties of Pr3+-doped fluorophosphate glasses and their induced defects by gamma irradiation

Multicomponent fluorophosphate host glass and samples containing Pr2O3 as dopant oxide with added (0.25, 0.5, 1.0 or 2 wt%) were prepared by melting and annealing technique. Multiple characterization techniques were employed to investigate optical, photoluminescence and FTIR spectral properties of the prepared glasses before and after being gamma irradiated with doses of 2, 9 Mrad. Optical absorption spectra reveal only distinct UV absorption in the undoped glass which is related to trace iron impurities while the Pr2O3-doped samples exhibit two series of characteristic extended peaks within the visible and near-IR regions which are due to absorption of Pr3+ ions. Gamma irradiation causes a continuous increase of the intensity of the UV absorption with irradiation. The Pr2O3-doped samples reveal obvious effects including the shift of the absorption to longer wavelength only of the first visible series of absorption peaks while the second series of peaks in the near IR region remain almost unchanged. These optical changes upon irradiation are suggested to be related to photochemical reactions with the liberated pairs of electrons and positive holes during the irradiation process. Photoluminescence (PL) measurements indicate the appearance of five emission peaks and three excited peaks before irradiation and their intensities increase with the Pr2O3 content. With irradiation, the PL spectra reveal limited changes with 2 Mrad but with 9 Mrad, the first emission peaks show few variations but the main high intense peak at 600 nm remains unchanged but the intensities of the peaks become very close with the increase of Pr2O3 content. The PL results support the stability of the Pr3+ ions as evidenced by the persistence of the optical absorption spectra. FTIR spectra of the studied glasses reveal the appearance of repetitive vibrational bands due to main building PO4 units mainly with Q2 and Q3 units with some suggested fluorophosphates groups (PO3F)− AlF4 (AlFO) groups. Gamma irradiation decreases the intensities of some bands together with the generation of a distinct band at 1455 cm−1. The FTIR results indicate the maintenance of the vibratonal bands after irradiation and the changes in the intensity of some bands are related to suggested variations in the bond angles and/or bond lengths of structural phosphate groups.

Impact effects of gamma irradiation on the optical and FT infrared absorption spectra of some Nd3+–doped soda lime phosphate glasses

The main aim of the present work is to study by two collective optical and FTIR spectral measurements some prepared Nd2O3–doped soda lime phosphate glasses before and after gamma irradiation with dose (9 Mrad). The spectral data reveal two strong UV absorption peaks which are correlated with unavoidable trace iron impurities beside extended additional characteristic bands due to Nd3+ ions. Gamma irradiation on the undoped glass produces slight decrease of the intensity of the UV absorption and the generation of an induced visible band and these effects are controlled with two photochemical reduction of some Fe3+ ions to Fe2+ ions together with the formation of nonbridging oxygen hole center (NBOHC) or phosphorous oxygen hole center (POHC). The impact effect of gamma irradiation on the spectra of Nd2O3–doped glasses is limited due to suggested shielding behavior of neodymium ions. FT–infrared spectra show vibrational modes due to main Q2–Q3 phosphate groups and the response of gamma irradiation of the IR spectra is low and the limited variations are related to suggested changes in some bond angles and bond lengths which cause the observed decrease to the intensities of some IR bands.

Shielding Behavior of Gamma-Irradiated MoO3 or WO3-Doped Lead Phosphate Glasses Assessed by Optical and FT Infrared Absorption Spectral Measurements

Undoped and MoO3- or WO3- doped lead phosphate glasses were prepared by the melting-annealing technique. The glasses were characterized through UV-visible and infrared measurements which were repeated after gamma irradiation. Optical spectrum of binary lead phosphate glass shows distinct ultraviolet bands correlated with unavoidable trace iron impurities within the chemicals used for the preparation of the glasses. UV-visible absorption spectra of MoO3- or WO3- doped glasses exhibit additional UV-visible bands which are related to the presence of four oxidation states of the two transition metal (molybdenum or tungsten) ions (Mo3+, Mo4+, Mo5+, Mo6+, W3+, W4+, W5+, W6+). The extra UV band is related to hexavalent (5d0) state while the rest of the visible bands are related to (350–440 nm - trivalent state), (450, 550, 650 nm - tetravalent state) while the broad band centered at about 770 nm (pentavalent state). The intensities of the absorption bands are observed to change with the transition metal content and their valencies. Infrared absorption spectra reveal distinct vibrational bands which are assigned to phosphate groups with sharing of Pb-O vibrations within both the range 460–620 cm-1 and the range 900–1100 cm-1 revealing a compact network structure. Gamma irradiation causes a minor increase in intensity of one of the UV band due to suggested photo-oxidation of some trace ferrous ions to additional ferric ions but the remaining spectral curve remains unaffected which is obviously related to some shielding effects of heavy atomic weight of PbO. This heavy metal oxide (PbO) is assumed to retard or prohibit the free passage of free electrons or positive holes generated during the irradiation process.

Study on the reducing effect of γ-irradiation on Sm3+ doped LiAl fluorophosphate glasses through optical, structural and luminescence analysis

Undoped and (0.2, 0.5, 1, 3%) Sm2O3-dopants within host LiAl fluorophosphate glasses of the basic composition mol% (P2O5 70, LiF 20, AlF3 10) were prepared. The glasses were characterized by studying their optical, FT infrared and photoluminescence spectra before and after successive γ-radiation (0.25, 1, 3 Mrad). The strong absorption in the UV wavelength region of the optical spectra has been related to trace iron impurity. The Sm3+ ions reveal their characteristic peaks arranged into two groups from about 330 to 460 nm and from 950 to 1550 nm. The major spectra of Sm3+ ions are assumed to be due to transitions from 6H5/2 level to various excited 2s+1Lj levels. The photoluminescence spectra show four emission lines at 560, 596, 642 and 702 nm and their intensities increase with Sm2O3 content. Gamma irradiation produces limited variations in the optical spectra. Examinations of the excitation and emission spectra of the studied glasses at λem = 600 and λex = 402 nm show results supporting the stability of Sm3+ ions after gamma irradiation. However, the change of the excitation wavelength to λex = 535 nm reveals the appearance of two additional peaks which are related to partial reduction of some Sm3+ ions to Sm2+ ions through suggested photoreduction by capturing librated electrons during the radiation process. FTIR spectra of the studied glasses reveal similar vibrational modes related to Q2 and Q3 phosphate groups due to the high content of P2O5 in the glass composition (70 mol%) together with some suggested mixed fluorophosphate groups (PO3F)2−. Gamma irradiation shows limited variations in the FTIR spectra due to the proposed presence of AlF4 and/or AlF6 groups which conduct stability to the glass network.

Optical and structural investigation on sodium borosilicate glasses doped with Cr2O3

In this work, Sodium borosilicate glasses with chemical composition of 60% SiO2–20% B2O3–20%Na2O doped with different contents of Cr2O3 were prepared by melting-quenching method. Physical, structural and optical properties of glasses were investigated by studying density and molar volume, Fourier Transform Infrared (FT-IR) Spectra and UV–visible absorption spectroscopy. The results showed an increase in density of glasses with the increase of Cr2O3 that can be due to addition of oxide with high molar mass. The optical absorption spectra of un-doped glass reveals UV absorption due to trace iron impurities with no visible band however Cr2O3 doped glasses shows absorption in visible range that are characteristic. Increasing of Cr3+ ions in the glassy microstructure of samples provides a semiconducting character to Sodium borosilicate glass by reducing the direct and indirect optical band gaps of glass samples from 3.79 to 2.59 (ev) and 3.36 to 2.09 (ev), respectively. These changes could be attributed to the role of Cr3+ ions as the network former which asserts improvement of semiconducting behavior in presence of Cr2O3.

Manifestation and Role of B2O3 in High Lead Containing Silicate Glasses

Glass matrices of nominal composition 90% PbO-10% SiO2 with progressive partial replacement of PbO by B2O3 have been prepared using the conventional melting and annealing method. Collective Fourier transform infrared (FTIR) and optical absorption spectral measurements recorded before and after irradiation with a final gamma ray dose (8 Mrad) were employed to manifest the role of B2O3 on the studied properties of high lead silicate glasses. Optical spectra reveal extended UV/vis. absorption spectral bands resulting from absorption from both lead ions and trace iron impurities. FTIR absorption spectral measurements indicate the appearance of compact mid IR spectra correlated with the presence of multifunctional mixed vibrating groups including SiO4, BO3, BO4 and PbO4. The application of the deconvolution analysis technique (DAT) enables the identification of mixed or hidden peaks associated with different vibrational modes due to the expected structural groups from silicate and Pb-O linkages. Gamma irradiation of glasses produces stable and slightly affected spectral bands which can be assigned to the presence of lead oxide in high percent which causes shielding and retarding characteristics towards gamma irradiation to reduce passage of generated positive holes and electrons throughout the irradiation process.

Trace iron impurities deactivate palladium supported on nitrogen-doped carbon nanotubes for nitrobenzene hydrogenation

Nitrogen-doped carbons can effectively stabilize noble metal particles to achieve high catalytic performances. However, the metallic impurities in carbon nanomaterials, e.g. the residual growth catalysts of carbon nanotubes (CNTs), have some unforeseen effects on the catalysis involving nanocarbons. Herein, we demonstrate that the residual growth catalysts of N-doped CNTs (NCNTs) may significantly deactivate Pd catalysts for the hydrogenation of nitrobenzene. Through high-resolution transmission electron microscopy and CO-stripping, it was determined that the N dopants improved the dispersion of Pd nanoparticles. However, the iron, at ppm level, in residual catalysts encapsulated inside NCNTs can transfer onto the surface of Pd to block active sites so that the activity of Pd/NCNTs was much lower than that of Pd/CNTs. The similar effect was observed for most of the common metallic impurities in carbon materials, including Co, Ni, Mn, Cr, Cu, Zn, Mo, Al and Mg. To exploit the N-doped carbons, we deposited N-doped carbon layers on purified CNTs through pyridine pyrolysis and then supported Pd nanoparticles. By this means, the activity of Pd for nitrobenzene hydrogenation was improved by 3.85 folds compared to conventional CNTs, emphasizing the importance of controlling impurities in N-doped carbon materials for high performance catalysts.

Gamma ray interaction with vanadyl ions in barium metaphosphate glasses; spectroscopic and ESR studies

Optical, FTIR, ESR investigations of prepared undoped barium metaphosphate glass and other samples with the same basic composition containing varying V2O5 contents (0.5, 1, 2, 3%) were carried out before and after gamma irradiation. The undoped glass shows a strong UV optical absorption which is correlated with unavoidable contaminated trace iron impurities. The V2O5-doped samples reveal two additional strong broad visible bands centered at 450 and 680 nm. Such extra peculiar and strong two broad visible bands are related to both tetravalent and trivalent vanadium ions in measurable percent due to the reducing behavior of barium phosphate host glass. Gamma irradiation on the undoped glass results in the generation of collective induced UV and visible bands which are originating from positive hole and electron centers. Glasses containing V2O5 reveal upon gamma irradiation induced defects in the UV as the undoped sample together with distinct splitting within the first broad visible band while the second broad band remains unchanged. This behavior is related to limited photoionization upon the addition of V2O5 indicating specific shielding effect of the vanadium ions towards gamma irradiation. It was noticed that irradiation causes no distinct variations in the FTIR spectra due to the presence of 50% of heavy metal oxide (BaO) and some shielding effect of vanadium ions.

Gamma rays Interactions with Bismuth Phosphate Glasses Doped with 3d Transition Metal Oxides

Bismuth phosphate glasses of the basic composition (Bi2O3 30 mol%-P2O5 70 mol%) with additional dopants 3d TM oxides (0.2 wt%) were prepared by the melting and annealing technique. Combined optical (UV/vis.) and FT infrared absorption spectra were measured for the prepared samples before and after gamma irradiation with a dose of 8 Mrad (8×104 Gy). Optical spectra reveal strong UV absorption bands due to trace iron impurity together with an additional absorption band due to Bi3+ beside characteristic absorption related to specific 3d TM ions with preference for the lower valences due to the reducing effect of phosphate host glass. FTIR spectra show vibrational bands due to phosphate chains with the sharing of absorption bands due to Bi-O vibrations. Gamma irradiation causes limited changes due to the presence of heavy metal Bi3+ ions which show some shielding behavior towards gamma irradiation as revealed by optical and FT infrared absorption measurements. Some suggested photochemical reactions are forward to interpret the changes in the UV spectra beside the formation of an induced phosphorus oxygen hole center (POHC) in the visible region.

Photoluminescence and spectral performance of manganese ions in zinc phosphate and barium phosphate host glasses

Zinc and barium metaphosphate glasses containing dopants of MnO2 (2, 4, 8%) were prepared. Collective studies were carried out through optical, photoluminescence and Fourier transform infrared (FTIR) spectral measurements for the prepared glasses before and after gamma irradiation. Electron spin resonance (ESR), thermal expansion and crystallization studies were also investigated. Optical spectra for undoped and MnO2–glasses reveal strong ultraviolet (UV) absorption due to trace iron impurity in the materials used for preparation of glasses and Mn2+ ions are not identified due to spin–forbidden nature of their spectra. Upon gamma irradiation, the MnO2–doped glasses reveal extension of the UV absorption exhibiting two peaks together with the generation of an induced broad visible band centered at 570–580nm. Extra two glasses doped with 8% MnO2 were melted under reducing condition and they showed characteristic band at 410nm related to Mn2+ ions absorption. Photoluminescence (PL) spectra reveal two excitation peaks in MnO2–doped zinc phosphate glasses at 348 and a sharp peak at 410nm while the MnO2–doped barium phosphate glasses exhibit a sharp peak at 410nm and a curvature at 348nm. The emission spectra show a broad band centered at 620nm in both glasses but with a curvature at 605–610nm in zinc phosphate glasses which are correlated with the transition 4T1g→6A1g.The efficiency of the photoluminescence increases with the MnO2 content and the heat treatment. The values of the optical band gap (Eopt) and Urbach energy (∆E) were calculated. FTIR spectra reveal vibrational bands due to phosphate network mainly of metaphosphate groups but in zinc phosphate glasses, the mid spectra show compact network because of the ability of Zn2+ ions to participate partly as ZnO4 or P–O–Zn linkages. Thermal expansion data show different responses. Zinc phosphate glasses show anomalous behavior related to the change in the coordination of zinc cations while barium phosphate glasses exhibit normal expansion because Ba2+ ions exist only as modifiers. The crystallization behavior reflects also anomalous behavior. The zinc phosphate glass crystallizes in two crystalline species, mainly zinc metaphosphate phase and another zinc phosphate (3ZnO·P2O5) phase while the barium phosphate glass crystallizes only in barium metaphosphate phase.

The effect of Li2O and LiF on structural properties of cobalt doped borate glasses

Two glassy (LiF–B2O3) and (Li2O–B2O3) systems containing different content of CoO dopants (0.05, 0.1, 0.15, 0.2wt%) were prepared. UV/Vis optical absorption of base glasses reveals a strong UV absorption bands attributed to unavoidable contaminated trace iron impurities. CoO-doped glasses show extra three visible bands due to both octahedral and tetrahedral Co2+ ions related to the little variation between energies of ligand field stabilization between the two coordination states. Fluoride containing glasses show limited variations in the spectral properties due to the different ligand strength of the anions (F− and O2−). FTIR spectra display characteristic modes of vibrations due to triangular and tetrahedral borate groups. It is assumed that LiF acts as Li2O in promoting the formation of tetrahedral (BO3F) units which possess the same wavenumber position for vibrations of (BO4) units in the range of 800–1200cm−1. CoO causes no distinct variations in number or position of characteristic IR vibrational bands due to their low dopant level (0.05–0.2%). A new suggested trial has been utilized to calculate the percent of four coordinated borons from both optical and FTIR spectra to give more insight on the role of CoO as dopant on these spectral properties and on the calculated parameters.

Effect of TiO2 on the optical, structural and crystallization behavior of barium borate glasses

Collective characterizations of prepared binary barium borate glass (50 mol % BaO – 50 mol % B2O3) together with samples containing increasing added TiO2 contents (5% → 30%) were carried out by optical and FT infrared absorption measurements. FT infrared and X-ray diffraction analysis were done for heat treated glass – ceramic derivatives prepared through two step regime process. Optical spectra of the glasses reveal the presence of titanium ions mainly in the tetravalent state imparting additional UV band beside strong UV absorption due to trace iron impurity. IR spectral studies indicate the presence of triangular and tetrahedral borate groups through the modification of BaO to some BO3 to BO4 groups beside the presence of titanium ions as interfering or overlapping TiO4 or BOTi groupings in the glassy network. Crystalline X-ray diffraction results indicate the separation of crystalline barium borate of the composition (2BaO.5 B2O3) as a main constituent together with some crystalline alkali titanates confirming the role of TiO2 of both as nucleating agent beside acting as structural forming through reaction with alkali oxides to form crystalline titanates. The optical band gap values reveal progressive decrease and increase of Urbach energy with TiO2 content and the same for the refractive index values and all these parameters are correlated with the proposed changes in the glass constitution with the introduction of TiO2. The additional thermal expansion measurements indicate the peculiar characteristic negative expansion up to 300 °C and after which an increase in the coefficient of thermal expansion is identified with the increase in temperature. The thermal parameters are also correlated with the modification of the glass structure by the introduction of titanium ions.

Comparative Studies of IR Spectra, Optical and Thermal Properties of Binary CdO-B2 O 3, SrO-B2 O 3, and BaO-B2 O 3

Binary glasses of barium borate, strontium borate, and cadmium borate systems were prepared by melting and annealing techniques. Combined optical (UV-visible) and infrared absorption spectral measurements of the prepared glasses were carried out before and after gamma irradiation with a dose of 8 Mrad (8x10 4Gy). Optical results reveal that the glasses possess excellent transmission in the visible region but the presence of unavoidable trace iron impurity within the chemicals even in the ppm level imparts strong absorption in the UV region. Infrared absorption spectra indicate the presence of both triangular and tetrahedral borate groups as structural building units which brings stability to the glassy network. Gamma irradiation causes limited induced defects due to the presence of heavy alkaline earth ions in high percent in their chemical composition (40 mol%) which confirms their usefulness as radiation shielding materials. Thermal properties of the prepared glassy samples were obtained by measuring their thermal expansion coefficients and deriving transformation and softening temperatures. The thermal data indicate that these glass systems can be used as promising sealing candidates.

Optical stability of 3d transition metal ions doped-cadmium borate glasses towards γ-rays interaction

This work reports the preparation of glasses of binary cadmium borate with the basic composition (mol% 45 CdO 55 B2O3) and samples of the same composition containing 0.2 wt% dopants of 3d transition metal (TM) oxides (TiO2 → CuO). The glasses have been investigated by combined optical and Fourier Transform infrared spectroscopic measurements before and after being subjected to gamma irradiation with a dose of 8 Mrad (8 × 104 Gy). Optical absorption of the undoped glass before irradiation reveals strong charge transfer UV absorption which is related to the presence of unavoidable contaminated trace iron impurities (mainly Fe3+) within the raw materials used for the preparation of the base cadmium borate glass. The optical spectra of the 3d TM ions exhibit characteristic bands which are related the stable oxidation state of the 3d TM ions within the host glass. Gamma irradiation produces some limited variations in the optical spectra due to the stability of the host glass containing high percent 45 mol% of heavy metal oxide (CdO) which causes some shielding effects towards irradiation. From the absorption edge data, the values of the optical band gap Eopt and Urbach energy (∆E) have been calculated. The values of the optical energy gap are found to be dependent on the glass composition. Infrared absorption spectral measurements reveal characteristic absorption bands due to both triangular and tetrahedral borate groups with the BO3 units vibrations more intense than BO4 units due to the known limit value for the change of BO3 to BO4 groups. The introduction of 3d TM ions with the doping level (0.2 wt%) causes no changes in the number or position of the IR bands because of the presence of TM ions in modifying sites in the glass network. It is observed that gamma irradiation causes some limited changes in the FT-IR spectral bands due to the stability of the host heavy cadmium borate glass.

Integration Between Optical and Structural Behavior of Heavy Metal Oxide Glasses Doped with Multiple Glass Formers

Heavy metal oxide glasses (composition 60 PbO, 20 Bi2O3 mol%) and containing 20 mol% conventional glass formers SiO2, B2O3, and P2O5 were prepared. Combined optical and Fourier transform infrared absorption spectra were measured for the prepared glasses to justify the role of glass formers in the optical spectra together with the network structural groups in such glasses. Also, the density and molar volume values were calculated to obtain some insight on the compactness and arrangement in the network. Optical measurements have been used to determine the optical band gap (Eg), Urbach energy (ΔE) and the refractive index (n). Optical spectra of all the samples reveal strong UV absorption which is related to the presence of unavoidable trace iron impurities (Fe 3+ ions) contaminated within the raw materials which were used for the preparation of the studied glasses. Additional near visible bands are observed in all prepared glasses due to characteristic absorption of Pb 2+ and Bi 3+ ions. Furthermore, The variations of the luminescence intensity, values of the optical band gap, band tail, and refractive index can be understood and related in terms of the structural changes that take place in the glass samples. The infrared absorption spectra of the prepared glasses show characteristic absorption bands related to the borate or silicate or phosphate network (BO3, BO4, SiO4, PO4 groups) together with vibrational modes due to Bi-O and Pb-O groups.

Hydrogenated Graphenes by Birch Reduction: Influence of Electron and Proton Sources on Hydrogenation Efficiency, Magnetism, and Electrochemistry.

Interest in chemical functionalisation of graphenes today is largely driven by associated changes to its physical and material properties. Functionalisation with hydrogen was employed to obtain hydrogenated graphenes (also termed graphane if fully hydrogenated), which exhibited properties including fluorescence, magnetism and a tuneable band gap. Although the classical Birch reduction has been employed for hydrogenation of graphite oxide, variation exists between the choice of alkali metals and alcohols/water as quenching agents. A systematic study of electron (Li, Na, K, Cs) and proton sources (tBuOH, iPrOH, MeOH, H2O) has been performed to identify optimal conditions. The proton source exerted a great influence on the resulting hydrogenation with water and out-performed alcohols, and the lowest carbon-to-hydrogen ratio was observed with sodium and water with composition of C1.4H1O0.3. Although ferromagnetism at room temperature correlates well with increasing hydrogen concentrations, small contributions from trace iron impurities cannot be completely eliminated. In contrast, hydrogenated graphenes exhibit a significant paramagnetic moment at low temperatures that has no correlation with impurities, and therefore, originates from the carbon system. This is in comparison to graphene, which is strongly diamagnetic, and concentrations of paramagnetic centres in hydrogenated graphenes are one order of magnitude larger than that in graphite. Nonetheless, hydrogenation over a particular level might also excessively disrupt intrinsic sp(2) conjugation, resulting in unintended reduction of electrochemical properties. This was observed with heterogeneous electron-transfer rates and it was postulated that hydrogenated graphenes should generally have high defect densities, but only moderately high hydrogenation, should they be employed as electrode materials.

Synthesis and Spectral Properties of Nd2O3-Doped Sodium Silicophosphate Glass

Combined UV-visible and FTIR spectral studies of undoped and Nd2O3 –doped sodium silicophosphate glasses were carried out to characterize the optical and structural properties of such glasses. The base undoped silicophosphate glass exhibits strong UV absorption which is due to the presence of unavoidable trace iron impurities (mainly Fe3+ ions) present contaminated within the raw materials used for the preparation of such glasses. Nd2O3 –doped glasses show characteristic absorption bands extending in the entire visible region which are attributed to the contribution of Nd3+ ions with distinct peaks which are almost constant with the increase of dopant. This comes from the combined compact glass structure containing two glass forming units and the shielding of the rare-earth ions. Infrared absorption spectra of the studied glasses reveal characteristic IR bands due to the combination of both silicate and phosphate groups. The introduction of Nd2O3 within the dopant level (2 %) produces no variations in the IR vibrational bands due to the presence of the two structural silicate and phosphate groups giving compactness of the network structure. The deconvoluted spectra reveal the presence of phosphate groups in a slightly high ratio due to the high content of P2O5 in the composition.

Photoluminescence and spectroscopic dependence of fluorophosphate glasses on samarium ions concentration and the induced defects by gamma irradiation

Combined optical, FTIR and photoluminescence spectra of varying Sm3+ ions in NaF–AlF3–phosphate glasses were investigated before and after successive gamma irradiation. Optical (UV–visible) absorption of the base undoped glass reveals UV absorption which becomes broadened and strong with progressive gamma irradiation. The UV absorption of the undoped glass is related to unavoidable trace iron impurity (Fe3+) contaminated within the chemicals used for its preparation. Upon gamma irradiation, ferrous ions present in noticeable percent within the impurity due to the reducing nature of phosphate glass interact with positive holes during the irradiation process and are transformed to ferric ions through photochemical reactions and the additionally formed Fe3+ ions impart their characteristic strong absorption in the UV region. Sm3+ containing glasses show characteristic small peaks arranged into two regions from about 350 to 900nm and from about 1000 to 1600nm. Such absorption peaks are more distinct with the increase of Sm2O3 content. Most of the limited number of absorption peaks are due to transitions from the 6H5/2 level to the various excited 2s+1LJ levels. The majority of the transitions in the spectra are assumed to originate from induced electric dipole (ED) interactions with the selection rule ∆J≤6. The intense band 6P3/2←6H5/2 around 25,000cm−1 (~400nm) is spin-allowed. The emission spectra of Sm2+ ions were recorded under the excitation wavelength of 402nm for all prepared Sm2O3-containing glasses. The photoluminescence spectra show four emission lines, of which three consist of strong bands while the last line is a weak band. The wavelengths of the four luminescence peaks occur at about 560, 596, 642 and 702nm and they are assigned to transitions from 4G5/2 to 6H5/2, 6H7/2, 6H9/2 and 6H11/2, respectively. The intensity of the emission spectra is observed to increase with the increase of Sm2O3 content. The optical spectra within the visible–near IR region and photoluminescence spectra of Sm2O3-doped glasses are found to be stable and show almost no variations after gamma irradiation especially when rare-earth ions are present in noticeable contents (1–3%). FTIR spectra of all the studied glasses reveal repetitive and characteristic vibrational bands mainly due to phosphate groups with abundant of Q2 and Q3 groups due to the high content of P2O5 (70mol%). The introduction of 10% NaF and 20% AlF3 is observed to cause formation of mixed fluorophosphate groups (PO3F)2−. The formation of (AlPO)4 and/or (AlPO6) groups needs further justification by combined techniques. The increase of Sm2O3 content to 3% causes obvious increase of the IR absorption bands within the wavenumbers range of about 850–1400cm−1 due to suggested depolymerization effect. Gamma irradiation causes no distinct variations in the FTIR spectra due to suggested compactness through the formation of additional structural groups from AlF4 or AlF6.

Influence of CuO content on the structure of lithium fluoroborate glasses: Spectral and gamma irradiation studies

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 310nm 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 520nm. The CuO doped glasses reveal the same UV absorption beside a very broad visible band centered at 780nm 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.

Structural and Optical Correlation of Gamma-Irradiated 3d Transition Metals-Doped Lithium Disilicate Glasses

Undoped lithium disilicate glasses together with glasses of the same nominal composition containing 0.2 % of one of the 3d transition metal oxides (TMO) were prepared. Combined optical and FT infrared absorption spectral analysis were carried out for the prepared glasses before and after gamma irradiation with a dose of 8 Mrad. The optical spectrum of undoped glass reveals strong UV absorption which is related to the presence of unavoidable trace iron impurities (mainly Fe3+ ions). UV/Visible absorption spectra of 3d TM ions show additional characteristic absorption bands due to each respective TM ion. The TM ions mostly exhibit the higher valance or tetrahedral coordination states. Gamma irradiation of the undoped glass produces some variations in the optical spectra. The UV spectra reveal a slight increase in intensity while the visible spectra exhibit an induced defect at about 420 nm due to a silicon oxygen hole center or a nonbridging oxygen hole center. Some TM ions are assumed to share or compete for generated electrons and positive holes during the irradiation process. Infrared absorption spectra of the glasses reveal repetitive characteristic vibrational bands due to bending, symmetric stretching and antisymmetric stretching of the Si-O-Si or O-Si-O modes in the silicate network. The introduction of TM ions within the doping level (0.2 %) causes no effect on the IR spectra. The minor effects of irradiation on the IR spectra are related to some changes in the bond angles and/or bond lengths of some structural building units.