FTIR and UV–VIS optical absorption spectra of gamma-irradiated MoO3-doped lead borate glasses

Structure and optical properties of MoO₃-doped lead borate glasses which contain high PbO content (60, 70 and 80%) have been studied using Fourier transform infrared (FTIR) and ultraviolet–visible (UV–VIS) spectroscopic tools. FTIR spectra reveal absorption bands which are characteristic for various structural units of borate network, mainly BO₃ triangles and BO₄ tetrahedra, in addition to the PbO_n (where n = 3 and/or 4) structural units. UV–VIS optical absorption spectra reveal broad intense charge transfer UV bands due to Pb^2 + ions in the range 320–385 nm. Within this range, molybdenum ions, preferably Mo^3 + and Mo^5 +, can interfere at about 360–385 nm. Additionally, molybdenum ions give a weak visible band at about 850–860 nm. The optical absorption spectra of the studied glasses show marked resistance to successive gamma irradiation up to 5 Mrad. This shielding behavior can be related to the present high content of the high atomic mass Pb^2 + ions. Changes in the atomic structure before and after gamma irradiation are described and explained.     

UV–visible and infrared absorption spectra of transition metals-doped lead phosphate glasses and the effect of gamma irradiation

Undoped and transition metals (TM 3d)-doped lead phosphate glasses were prepared. Ultraviolet–visible absorption spectra were measured in the range 200–1100 nm before and after successive gamma irradiation. Experimental results indicate that the undoped lead phosphate glass reveals before irradiation strong and broad ultraviolet absorption which is related to the co-sharing of absorption due to both trace iron impurities and lead ions (Pb²⁺). In the TM-doped glasses, characteristic absorption bands are obtained in both the UV and/or visible regions due to each respective TM ion in addition to that observed by the base undoped UV absorption. Gamma irradiation produces with the undoped glass a prominent induced ultraviolet broad band centered at about 300 nm originating mostly from the contribution of trace iron impurities and the visible spectra reveal markedly high shielding behavior towards successive gamma irradiation, due to the presence of both high content of heavy Pb²⁺ ions and the sharing of phosphate as a partner. With TM-doped samples, the observed induced bands are virtually varying and related to the type of the sharing TM ions. Infrared absorption spectra reveal in the undoped and TM-doped glasses characteristic structural phosphate groups mainly consisting of metaphosphate and pyrophosphate units. Transition metals are assumed to cause depolymerization of the phosphate glass network with different ratios but the changes in IR spectral data are limited due to the low doping level. Gamma irradiation of the samples is assumed to cause changes in the bond angles or bond lengths of the structural phosphate units within network as evident in the variation of the intensities of the IR bands.     

Redox reactions during temperature change in soda-lime–silicate melts doped with copper and iron or copper and manganese

Glasses with the base composition 16Na₂O · 10CaO · 74SiO₂ doped with copper and iron or copper and manganese were studied by high temperature UV–vis–NIR spectroscopy. The spectra exhibited distinct absorption bands attributed to the respective transition metal ions present (Cu²⁺, Fe²⁺, Fe³⁺, Mn³⁺). In glasses doped with only one polyvalent element, the absorption decreases linearly with increasing temperature, the absorption bands are shifted to smaller wave numbers and get broader. In glasses doped with two types of transition metals, the situation is the same up to a temperature of around 550 °C. At larger temperature, the Cu²⁺-absorption in glasses also co-doped with iron increases again, while in glasses doped with both copper and manganese the absorption is approximately the same as in glasses solely doped with copper. It is shown that this is due to redox reactions between polyvalent species. These reactions are frozen in at temperatures <550 °C.     

The effect of copper ions addition on structural and optical properties of zinc borate glasses

Glasses in the ternary system xCuO?(100 ? x)[55B₂O₃·45ZnO] (0 ≤ x ≤ 20 mol%) have been prepared by melting at 1200 °C and rapidly cooling at room temperature. The effect of copper ions addition in 55B₂O₃·45ZnO glass matrix together with the matrix effect on paramagentic behavior has been investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential thermal analysis (DTA), electron paramagnetic resonance (EPR), ultraviolet–visible (UV–VIS) spectroscopy and density measurements. The increase of the number of non-bridging oxygen (NBO) atoms as a function of CuO content in these glasses leads to the decrease of glass polymerization which reduces the stability of the glasses and favors the association of copper ions in clusters. This leads to the major changes of structural and optical properties of the studied glasses as can be seen from the data obtained by FTIR and EPR spectroscopies.     

Spectroscopic studies of gamma irradiated Nd doped phosphate glasses

Ultra violet-visible (UV-Vis) and Fourier transform infrared (FT-IR) spectra of Nd doped phosphate glasses have been studied before and after gamma irradiation in order to understand the changes in the optical properties of glasses as well as to find the characteristics frequencies of the vibrational modes of chemical bonds, which decide the structural and spectral changes. UV, Vis, IR absorption and photoluminescence spectra of these glasses show changes depending on the composition of glass matrix. These changes are correlated on the basis of oxygen (O) and neodymium (Nd) concentration ratio obtained from energy dispersive X-ray spectroscopic (EDX) measurement. Gamma irradiation shows decrease in transmission below 700 nm for all the Nd³⁺ absorption lines from all the samples. Differential absorption spectra (UV-vis) of the samples before and after gamma irradiation show generation of some new bands below 700 nm along with dips (decrease) in the spectrum at the location of main Nd³⁺ absorption lines. This is attributed to the generation of different types of defects in the glass matrix along with possibility of change in the valence state of Nd³⁺ to Nd²⁺. IR absorption spectra of these glasses are found dominated mainly by the characteristics phosphate groups and water (OH) present in the glass network. The effects of gamma irradiation on IR absorption are observed in the form of bond breaking and possible re-arrangement of bonding. EDX and X-ray photoelectron spectroscopic (XPS) measurements indicate decrease in the relative concentration of oxygen in the glass samples after γ-irradiation.     

X-ray absorption spectroscopy and high-energy XRD study of the local environment of copper in antibacterial copper-releasing degradable phosphate glasses

Phosphate-based glasses of the general formula Na₂O–CaO–P₂O₅ are degradable in an aqueous environment, and therefore can act as antibacterial materials through the inclusion of ions such as copper. In this study, CuO and Cu₂O were added to Na₂O–CaO–P₂O₅ glasses (1–20 mol% Cu) and X-ray absorption spectroscopy (XAS) and high-energy X-ray diffraction (HEXRD) used to probe the local environment of the copper ions. Copper K-edge X-ray absorption near-edge structure (XANES) spectra confirm the oxidation state of copper to be predominantly 2+ in all samples regardless of which copper oxide was used in the preparation. The XANES results suggest the structural environment of copper to be octahedral with respect to oxygen in all samples. The HEXRD results yield a Cu–O nearest-neighbour distance of 1.98 Å and associated coordination number of approximately six, both consistent with octahedral coordination. Analysis of the extended X-ray absorption fine structure (EXAFS) data also yields structural parameters consistent with copper in an octahedral environment. The HEXRD and EXAFS results reveal a Cu–P distance of 3.13 Å, which confirms that the copper ions are coordinated within the phosphate glass network and not phase-separated in domains of copper oxide.     

Interaction of gamma rays with some sodium phosphate glasses containing cobalt

Undoped and cobalt-doped sodium phosphate glasses of various compositions and with varying cobalt contents were prepared. UV-visible absorption spectra were measured before and after successive gamma irradiation. Experimental results indicated that the undoped base glass reveals strong ultraviolet absorption which is related to the presence of unavoidable trace iron impurities in the raw materials. Cobalt-doped glasses show characteristic visible absorption bands which are related to the presence of Co²⁺ ions mostly in the tetra-coordination state. The generated induced color centers in the UV and visible regions by gamma irradiation are characterized in relation to intrinsic defects from the host base sodium phosphate glass and the extrinsic defects from both trace iron impurities and added doped cobalt ions. Infrared absorption measurements were carried out for some selected samples to identify the structural building groups in the studied glasses. Cobalt ions showed a shielding behavior towards the effects of progressive gamma irradiation especially in the visible spectral region.     

EPR and UV–Vis characterization of multicomponent germano-silicate glasses for photonics

Photosensitive, germanium-doped multicomponent silicate glasses with different amount of boron oxide and sodium oxide were prepared and investigated by means of electron paramagnetic resonance (EPR) and ultraviolet–visible (UV–Vis) spectroscopy in order to investigate the structural changes occurring in the glasses under UV laser irradiation at 248 nm (KrF excimer UV laser). Spectral data were recorded before and after UV laser irradiation: all the glasses showed EPR signals only after UV laser irradiation, independently from the presence of a UV–Vis absorption band on the as prepared glasses. The main results showed that the presence or the absence of boron and sodium and their amount play a role in the type and the number of defects, their time and thermal decay, under the same UV laser exposure conditions. A clear correlation between the EPR signal and the UV–Vis absorption is observed only for the 240 nm band. It is also demonstrated that the sodium ions decrease the number of paramagnetic defects in these glasses and deeply change the germano-silicate glass structure. The presence, the absence and the co-presence of sodium and boron ions has a role in the structure, the number, the nature and the stability of the paramagnetic defects. It is important to understand the role of sodium and boron in order to increase the photosensitivity of germano-silicate glasses, for their interest in the field of ion-exchangeable glasses for photonic waveguides and Bragg-grating based devices.     

Preparation and characterization of CuO doped Bi2O3–B2O3–BaO–ZnO glass system for transparent dielectric layer

The electrical, thermal, optical, and morphological properties of CUO doped Bi₂O₃–B₂O₃–BaO–ZnO glasses were studied as a PbO-free, low firing transparent dielectric layer for plasma display panels (PDP). CuO improved the transmittance of Bi₂O₃–B₂O₃–BaO–ZnO by up to 84% in the visible region, eliminating a yellowish color typical of Bi₂O₃–B₂O₃–BaO–ZnO. A slight absorption within the near infrared (NIR) region was also observed. The glass transition temperature (T_g), thermal coefficient of expansion (TCE), and root-mean square (rms) roughness of 0.005 wt% CuO doped Bi₂O₃–B₂O₃–BaO–ZnO were found to be 455 °C, 81.4 × 10⁻⁷/K, respectively, and 162 ± 14 Å, which satisfied the requirements for a transparent dielectric layer for PDP application.     

Alkaline earth zinc borate glasses doped with Cu2+ ions studied by EPR,optical and IR techniques

Copper ions incorporated into alkaline earth zinc borate glasses 10RO + 30ZnO + 60B₂O₃ (R = Mg, Ca and Sr) and 10SrO + (30 ? x)ZnO + 60B₂O₃ + xCuO (x = 0, 0.1, 0.3, 0.5, and 0.7 wt.%) were characterized by electron paramagnetic resonance (EPR), optical absorption and FTIR techniques. The EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu²⁺ ions. The values of spin-Hamiltonian parameters indicate that the Cu²⁺ ions in alkaline earth zinc borate glasses were present in octahedral sites with tetragonal distortion. The spin concentration (N) participating in resonance was calculated as a function of temperature for strontium zinc borate (SrZB) glass sample containing 0.7 wt.% of Cu²⁺ ions and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility (χ) was calculated at different temperatures and the Curie constant was evaluated from the 1/χ-T graph. The optical absorption spectra of these samples show only one absorption band. The optical band gap energies (E_g) and Urbach energy (ΔE) are calculated from their ultraviolet edges. The FTIR studies show different stretching and bending vibrations of alkaline earth zinc borate glasses.     

Photoinduced redox-reactions and transmission changes in glasses doped with 4d- and 5d-ions

(Fluoride)phosphate and borosilicate glasses of high intrinsic transparency in the deep ultraviolet (UV), were doped with 50–5000 ppm of the 4d- and 5d-ions Zr, Nb, Ta, Mo, or W. All of these ions absorb strongly in the UV. Samples plates were irradiated by UV lasers and the as a consequence generated various extrinsic and intrinsic defects were characterized by optical and EPR spectroscopy. The laser induced transmission changes depend not only on the glass matrix, but also on the valence of the dopants. Only fully oxidized d⁰-ions are observed in fluoroaluminate glasses. Laser irradiation photoreduces the d⁰-ions to extrinsic electron-centers (EC). Laser induced transmission changes extend from the UV up to 600 nm in the visible. The dopants are easily reduced to lower valences in metaphosphate glasses. Extrinsic hole centers (HC) replace intrinsic HC in samples containing the reduced transition metal ions. The strong transmission changes seen below 300 nm arise from intrinsic EC and extrinsic HC. The few remaining intrinsic HC (300–600 nm) recombine rapidly with EC or transform into more stable extrinsic HC. Borosilicate glasses show the formation of intrinsic boron oxygen hole center in the EPR spectra and of intrinsic HC and EC in the optical spectra. The d¹-ion Mo⁵⁺ is the only identified reduced dopant species in the borosilicate glasses. The band intensity of intrinsic EC in relation to intrinsic HC is correspondingly highest for the Mo-doped samples, in which extrinsic HC are generated.     

Luminescent properties and applications of Tb3+ doped silicate glasses with industrial scales

Tb³⁺ doped X-ray conversion glassy screen with an industrial scale (50 mm × 50 mm × 12 mm) was successfully fabricated, and its luminescent properties and applications in CCD imaging system were investigated. Results showed that Tb³⁺ doped silicate glasses mainly emit weak blue (400–460 nm) and strong green (480–570 nm) fluorescence. With the increase of Tb³⁺ ion concentration, the intensity of green emission increases, but that of blue emission decreases. Gd³⁺ ions can sensitize the luminescence of Tb³⁺ ions among silicate glasses. With the increase of CeO₂ concentration, the luminescent intensity of Tb³⁺ doped silicate glasses at 550 nm quickly decreases. However, the irradiation resistance of Tb³⁺ doped silicate glasses can be effectively improved by CeO₂ addition. The imaging quality of the luminescent glass screen is more excellent than that of Gd₂O₂S polycrystalline screens.     

Blue,green and red upconversions in Ho2O3-doped fluorophosphate glasses

Near infrared (NIR) to visible upconversions of a fluorophosphate glass of composition (mol%) 7Ba(PO₃)₂–32AlF₃–30CaF₂–18SrF₂–13MgF₂ doped with various concentrations (0.1, 0.3 and 1.0 mol%) of Ho₂O₃ have been investigated by exciting at 892 nm at room temperature. Three upconverted bands originated from the ⁵F₃ → ⁵I₈, (⁵S₂, ⁵F₄) → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions have been found to center at 491 nm (blue), 543 nm (green) and 658 nm (red), respectively. These bands have been justified from the evaluation of the absorption, normal (down conversion) fluorescence and excitation spectra. The upconversion processes have been interpreted by the excited state absorption (ESA), energy transfer (ET) and cross relaxation (CR) mechanisms involving population of the metastable (storage) energy levels by multiphonon deexcitation effect. It is evident from the infrared reflection spectral (IRRS) analysis that the upconversion phenomena are expedited by the low multiphonon relaxation rate in fluorophophate glasses owing to their high intense low phonon energy of ∼600 cm⁻¹ which is very close to that of fluoride glasses (500–600 cm⁻¹).     

Ag-doped antibacterial porous materials with slow release of silver ions

The inorganic–organic hybrids of polyethyleneglycol (PEG), tetraethoxysilane (TEOS) and triethylphosphate (TEP) doped by silver ions were prepared by sol–gel method. After molding and heating at 600 °C to remove organic components, porous Ag–P₂O₅–SiO₂ monoliths were obtained. Thermogravimetry (TG), differential thermal analysis (DTA), infrared spectra, ultraviolet–visible (UV–vis) spectra and pore structure of the samples were measured to show that organic components and residual water could be removed by a heat-treatment up to 600 °C and the mesopores with 6 nm pore diameter were formed. Specific surface area and pore volume of the samples were adjusted with different contents of TEP in the starting composition. Ag⁺ ions could be stably released into water at 30 °C up to 28 days. Antibacterial experiment showed that such materials treated at 600 °C could restrain Escherichia coli effectively.     

Structural modifications induced by addition of copper oxide to lead–phosphate glasses

xCuO(1-x)[P₂O₅·PbO] glass system with 0 ≤ x ≤ 50 mol% was prepared and investigated by means of EPR and IR spectroscopy in order to evidence the structural changes induced by different amounts of copper ions. EPR spectra analysis together with EPR parameters has indicated a distorted tetragonal symmetry – named tetrahedral local symmetry – for Cu^2 + ions in the studied glasses. A change in the shape of EPR spectra was also observed as for small CuO concentration (x < 20 mol%) these glasses present an asymmetrical line typical for isolated ions and for high CuO content this line is replaced by a symmetrical one characteristic of clustered ions through dipole–dipole interactions. IR spectra of the studied glasses put in evidence a strong depolymerization effect with a gradual increase of CuO. The shift of PO asymmetric stretching vibration band to lower wave number can be explained by the increase of PO₄ tetrahedra charge density leading a more ionic and less covalent bonding.     

Laser spectroscopy of Nd3+-doped PbO–Bi2O3–Ga2O3–BaO glasses

We present spectroscopic results of PbO–Bi₂O₃–Ga₂O₃–BaO glass doped with different concentration of Nd₂O₃. These glasses have high refractive index (∼2.4) and large spectral transmission window. Measurements of absorption, emission and fluorescence lifetime are presented. From the calculations of the Judd–Ofelt parameters the radiative lifetimes, branching ratios and quantum efficiency of ⁴F_3/2 level are calculated. The highest emission intensity was measured for the sample doped with 0.5 wt% of Nd₂O₃ with emission cross-section of 2.6 × 10⁻²⁰ cm², at 1069 nm, fluorescence lifetime of 110 μs, quantum efficiency of 82% and effective linewidth of 34 nm. The results point out this glass system as good candidate to be used in the development of photonic devices operating in the near infrared spectral range.     

Electronic transport properties of mixed transition metal ions doped borophosphate glasses

A series of borophosphate glasses in the composition (B₂O₃)_0.10–(P₂O₅)_0.40–(CuO)_0.50?x–(MoO₃)_x; 0.05 ? x ? 0.50 have been investigated for room temperature density and dc conductivity over the temperature range from 350 to 650 K. The density decreased with increase in MoO₃ over the composition range studied except a slight increase around 0.35 mole fraction. The observed initial decrease in conductivity with the addition of MoO₃ has been attributed to the hindrance offered by the Mo⁺ ions to the electronic motions. The observed peak-like behavior in conductivity in the composition range 0.20 – 0.50 mol% of MoO₃ is ascribed to the mixed transition metal ion effect (MTE). Mott’s small polaron hopping model has been used to analyze the high temperature conductivity data and the activation energy for conduction has been determined. The low temperature conductivity has been analyzed in view of Mott’s and Greaves variable range hopping models. It is for the first time that conduction mechanisms have been explored and MTE detected in mixed transition metal ions doped borophosphate glasses.     

Silver metal enhanced photoluminescence of Tm3+ doped GeS2–Ga2S3–CsCl glasses

We report silver metal enhanced near-IR and infrared-to-visible upconversion luminescence in Tm³⁺ doped 70GeS₂–10Ga₂S₃–20CsCl (in mol. %) glasses. The metal embedded glasses are prepared under controlled crystallization. Upon 808 nm excitation three fold enhancement of emissions is observed in the visible (446 nm, 496 nm, and 532 nm) and near infrared (1230 nm, 1450 nm and 1480 nm) regions. The possible mechanism responsible for the enhanced luminescence is discussed.     

Nano-composite soda lime silicate glass prepared using silver ion exchange

Commercial soda lime silicate glasses have been subjected to ion exchange at different temperatures ranging from 320 to 500 °C in a molten mixture of AgNO₃ and NaNO₃ with molar ratio of 10:90, 02:98 and 50:50 for different time periods ranging from 40 to 180 min. Optical and structural properties of the ion exchanged glass are measured using UV–Vis–NIR absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, fluorescence spectroscopy and transmission electron microscopy (TEM). Signature of silver nanoparticle formation is obtained from the UV–Vis–NIR spectra, which shows a peak at 425 nm due to surface plasmon resonance (SPR). Replacement of Na⁺ ions by Ag⁺ ions is inferred from FTIR spectra. Fluorescence spectra reveal the formation of Ag⁰ atoms from Ag⁺ ions at higher temperatures. TEM image shows the silver nanoparticles of average size 3.75 nm. At exchange temperature of 500 °C Ag nanoparticles are formed without post-exchange annealing treatment.     

Photoluminescence and structural studies on Na2O–PbO–SiO2 glasses

PbO_x[(Na₂O)_0.25(SiO₂)_0.75]_1−x glasses (with x = 0.1–0.30) were prepared by a conventional melt-quench method and characterized by UV–visible optical absorption, photoluminescence and ²⁹Si magic angle spinning nuclear magnetic resonance (MAS NMR) studies. It has been confirmed that the increased number of non-bridging oxygen atoms brought about by the increase in Q² structural units of silicon is responsible for the shifting of the wavelength corresponding to the onset of absorption, as PbO concentration increases in the glass. Emission in the visible region (400–450 nm), from these glasses has been attributed to the presence of L-centers, whose the peak maxima and line widths systematically shift to higher values by incorporating Pb²⁺ along with Na⁺ in the network modifying positions. All the Pb²⁺ ions in these glasses occupy only the network modifying positions, as revealed by the identical chemical shift values of Qⁿ structural units of silicon with increase in PbO concentration. In contrast to binary lead silicate glasses, no luminescence has been observed for comparable concentration of PbO, possibly due to the significant quenching of Pb²⁺ ions in the excited state.