Interaction of radiation-induced defects of glasses with CdSe and CdS nanocrystals

The influence of X-ray irradiation on the absorption spectra of commercial light filters based on the glasses containing selenium, cadmium, and sulfur has been investigated. The light filters were preliminary subjected to the heat treatment, which resulted in the precipitation of nanocrystals in the glass matrix. The irradiation leads to stationary partial bleaching of glasses. Analysis demonstrates that the difference spectra contain the induced absorption bands of conventional radiation-induced color centers of alkali silicate glasses and a fine structure. The fine structure closely resembles the known difference spectra obtained under the action of the external constant or low-frequency alternating electric field on glasses containing CdSe nanocrystals. The conclusion is drawn that the stable radiation-induced centers of the glass at the interface with nanocrystals serve as a source of the Coulomb field affecting the energy levels of the size quantization of the nanocrystals. It is suggested that nanocrystals of the type of the CdS_xS_1−x solid solutions in these glasses are either lacking or do not manifest themselves in the spectra after irradiation.     

Interaction of Gamma Rays with Calcium Aluminoborate Glasses Containing Holmium or Erbium

The optical absorption spectra of nominally pure and rare-earth-ion-doped (Ho³⁺ or Er³⁺) calcium aluminoborate (cabal) glasses were measured from 190 to 900 nm before and after γ-ray irradiation. The induced absorption spectra, calculated as the difference between the spectra of the irradiated and the unirradiated glasses, exhibit the characteristic absorption bands caused by the respective rare-earth ions. The intensity of the induced bands depends on the rare-earth oxide content. The response of the cabal glass to γ-ray irradiation is related to the formation of color centers associated with the intrinsic defects in the lattice structure of the cabal glass. The rates of formation and annihilation of the color centers are believed to approach saturation or equilibrium with prolonged irradiation.     

Interaction of γ-rays with Some Alkali-Alkaline-Earth Borate Glasses Containing Chromium

The change in the visible spectra of some irradiated ternary borate glasses containing chromium has been studied by increasing the γ-ray doses with changing alkali content or increasing chromium concentration. In the glass without chromium, the γ-rays induce two absorption bands which are attributed to the formation of positive hole centers, whereas in the glass containing chromium at least three absorption bands are observed. The results showed that the visible absorption bands before and after γ-ray irradiation exhibited changes with the radiation dose and/or the chemical composition of the glass. The response of the glasses to γ irradiation is related to the creation of defect color centers, the approach of a saturation condition, and the possible photochemical effect on the transition metal.     

Effect of Gamma Radiation on Optical and EPR Absorption Spectra of Phosphate and Fluoride Glasses Containing Lead

The induced optical and EPR absorption spectra of phosphate and fluoride glasses containing lead are investigated. It is revealed that exposure to gamma radiation leads to the formation of radiation-induced defects responsible for the induced absorption band with a maximum at 12500–13500 cm⁻¹ and the EPR signal in the form of an almost symmetric line with a g factor of 1.999 and a linewidth of ≈26 Oe. Analysis of the intensities of the absorption bands and the EPR signals in the spectra of glasses with low terbium, tin, and carbon contents and the study of their thermal bleaching demonstrate that the color centers are electron traps, whereas the paramagnetic centers are hole-trapping centers. Examination of the change in the parameters of the absorption bands in the spectra of glasses with different R ₂O contents (R = Na, K, Rb, Cs) makes it possible to determine the location of the color centers associated with the Pb⁺ ions in the structure. It is established that the glasses under investigation are characterized by the nonlinear absorption of radiation at a wavelength of 1.06 μm. The mechanism of formation of radiation-induced defects is considered. Original Russian Text Copyright ? 2005 by Fizika i Khimiya Stekla, Bocharova, Karapetyan.     

Radiation-induced color centers in γ-irradiated glasses in the Na2O-Nb2O5-P2O5 system

The specific features of the induced optical absorption spectra of glasses in the 45Na₂O · xNb₂O₅ · (55 ? x)P₂O₅ system with Nb₂O₅ contents x = 5, 10, 20, 25, 30, and 35 mol % are investigated as functions of the irradiation dose and the heat treatment time. The spectra are decomposed into Gaussian components with the use of computer processing. It is revealed that the glass composition and the irradiation dose affect the number, type, and parameters of the bands associated with the PO ₄ ^2? hole-type centers, electron-type color centers of the phosphate matrix, [Nb^(5+)?] one-electron centers, and [Nb^(5+)?-O-Nb^(5+)?] two-electron centers. The inference is made that heat treatment at temperatures close to the glass transition point T _g leads to the formation of groupings with a structure similar to structural motifs of NaNbO₃ crystals. It is demonstrated that these groupings are responsible for the induced optical absorption in the near-IR spectral range.     

Nature of Pd and Ti Metals in the Structure of CMAS Glass and Ceramics

The structure of electrically conductive CMAS‐TiO₂‐Pd glass and ceramics was investigated by transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), X‐ray photoelectron spectroscopy (XPS), X‐ray absorption near‐edge spectroscopy (XANES), and extended X‐ray absorption fine structure spectroscopy (EXAFS). The XANES spectra of Ti do not show any significant difference between the glasses ceramized in air or in a reducing “forming” gas, as well as between Pd‐containing versus Pd‐free samples, nor between surface versus bulk of the glass‐ceramic samples. However, EXAFS and XANES data recorded at the Pd K‐edge show significant dependences on whether the glass‐ceramic was ceramized in air or in “forming” gas. The XPS spectra of Ti 2p core‐level electrons for glasses ceramized in air or “forming” gas also show a strong difference depending on whether the samples did or did not contain Pd. STEM mapping confirms the existence of grains in the form of main crystalline phases identified with XRD, and also reveals the existence of Pd nanoparticles in glasses ceramized in both air and in “forming” gas.     

An Alternative Model for Photochromism of Glasses: Reversible Injection of Carriers from a Microcrystal and Its Surface States into Point Defects of Glass

The radiation-induced absorption spectra of photochromic homogeneous silicate glasses and heterogeneous borosilicate glasses containing AgCl, AgBr, or CuCl microcrystals are analyzed. The inference is made that these spectra contain the bands of traditional radiation-induced color centers (RICCs) in glasses and the bands of halide defects in microcrystals. The band model of the photochromic process in the microcrystal–surface states–glass system is proposed on the basis of the performed analysis with due regard for burning of the exciton hole in the induced spectrum of CuCl-containing glass. This model makes it possible to explain a large number of experimental data.     

Spinel ferrites NiFe2O4 NCs enhanced Mössbauer spectra,magnetization and Faraday rotation of diamagnetic tellurite glasses

Glass containing magnetic nanocrystals are attractive for obtaining high magnetic and magneto-optical properties. In this study, for the first time, 10 nm cubic NiFe₂O₄ (NFO) nanocrystals doped heavy metal oxide glasses were fabricated and the influence of NFO to glass structure, chemical bonds, Mössbauer spectra, magnetization and Faraday rotation was studied. X-ray diffraction, Raman and X-ray photoelectron spectra revealed the existence of multi-valence states of Fe/Ni ions, oxygen vacancies in cubic lattice and modifications on glass structure, which in turn adjusted the polarizability, oxygen packing density, Mössbauer spectra, magnetic property and magneto-optical behaviors. Through Mössbauer study, the increase of NFO amount enhanced the hyperfine field intensity of tetrahedral Fe³⁺ ions at the expense of octahedral ones. NFO doped glasses exhibited ferromagnetic behavior whose M_s and H_c increased with the NFO amount due to the NCs size effect. Verdet constant and Faraday rotation angle were studied as function of wavelength, magnetic field, polarizer angle and NFO amount. 3%NFO glass exhibited significant enhancement in magnetization and Verdet constant of 91 rad/T.m at 633 nm which is 5-fold of host glass and superior than literatures. In addition, due to the nanoscale NCs, the thermal stability of obtained NFO glasses remained higher than 100 °C which is promising for photonics devices fabrication.     

Ce3+‐ and Dy3+‐Doped Oxyfluoride Borosilicate Glasses with Near White Luminescence

A series of Ce³⁺/Dy³⁺‐doped oxyfluoride borosilicate glasses prepared by melt‐quenching method are investigated for light‐emitting diodes applications. These glasses are studied via X‐ray diffraction (XRD), optical absorption, photoluminescence (PL), color coordinate, and Fourier transform infrared (FT‐IR) spectra. We find that the absorption and emission bands of Ce³⁺ ions move to the longer wavelengths with increasing Ce³⁺ concentrations and decreasing B₂O₃ and Al₂O₃ contents in the glass compositions. We also discover the emission behavior of Ce³⁺ ions is dependent on the excitation wavelengths. The glass structure variations with changing glass compositions are examined using the FT‐IR spectra. The influence of glass network structure on the luminescence of Ce³⁺/Dy³⁺ codoped glasses is studied. Furthermore, the near‐ideal white light emission (color coordinate x = 0.32, y = 0.32) from the Ce³⁺/Dy³⁺ codoped glasses excited at 350 nm UV light is realized.     

Spectral-kinetic analysis of the photoinduced recombination of radiation-induced color centers in the sodium silicate glass

A technique for the spectral-kinetic analysis of the photoinduced recombination of radiation-induced color centers in glasses is developed. This technique is used to investigate the sodium silicate glass. The photoinduced absorption spectra of color centers are decomposed into individual Gaussian profiles, and the kinetic dependences of the intensities of these profiles are determined. The absorption spectrum associated with the radiation-induced color centers stable to optical radiation in the spectral range used in this study is separated from the total absorption spectrum of color centers. It is demonstrated that the absorption bands with maxima in the vicinity of 2.0, 2.8, and 4.0 eV are attributed to intrinsic hole centers of different types.     

Gamma-Ray Interaction with Lead Borate and Lead Silicate Glasses Containing Manganese

The optical absorption of high lead borate and lead silicate glasses containing manganese before and after γ-ray irradiation was studied. To separate the absorption due to manganese from the intrinsic absorption, blank glasses were prepared and measured. The results showed that the visible absorption band before and after irradiation exhibited changes with the radiation dose and chemical composition of the glass. The response of the glasses to gamma irradiation was related to the creation and spread of defect "color centers," the approach of a saturation condition, and the possible photochemical effect on the transition metal.     

Effect of CoO and Gamma Irradiation on the Infrared Absorption Spectra of Lithium Borate Glasses

Undoped and cobalt-doped lithium borate glasses (LBG) of various compositions, by varying cobalt contents were prepared by a conventional melt quenching technique. The density and molar volumes of the glass samples were estimated and; infrared absorption spectra were measured in the spectral range 400–1600 cm^?1before and after an irradiation dose of 50 kGy and 200 kGy. Experimental results showed that the density of studied samples increased as CoO increased while the molar volume decreased. FT-IR spectra of the prepared samples have been analyzed by the deconvolution of the spectra. A deconvolution technique is presented to make use of the BO₄ data and follow the change in the modifier and former fractions of CoO. FTIR was also used to study the glass system before and after gamma irradiation. The experimental results clearly indicate that after irradiation a significant change in the structure of the LBG glass network is observed. The modifying action of CoO on the glass composition is also studied. The glasses doped with 5 wt% of CoO are relatively more radiation resistant than the other compositions.     

Correlation between Macro- and Microstructural Changes in Ge:SiO2 and SiO2 Glasses under Intense Ultraviolet Irradiation

The photochemical transformation mechanism of defects in germanosilicate and silica glasses under ultraviolet (UV) laser irradiation has been investigated based on the changes in Raman spectra before and after irradiation. Two types of silica glasses, fused silica (type I) and dry synthetic silica (type IV), and germanosilicate optical fiber preforms were irradiated by intense UV photons from excimer lasers. Spectral changes in optical absorption and Raman spectra were examined to clarify a correlation between the microscopic defect formation and the macroscopic structural changes causing a photorefractive effect. Successive generation of E' centers through divalent centers is closely correlated with changes in Raman spectra, indicating that large structural changes in the glass network involved in this process would be the origin of photon-induced densification of the glasses. In addition, it has been proposed that the successive generation of E' centers is mediated by transient divalent centers converted from relaxed cation homobondings.     

Optical Properties and Effect of Gamma Irradiation on Bismuth Silicate Glasses Containing SrO, BaO or PbO

Optical and FT Infrared spectroscopic measurements have been utilized to investigate and characterize binary bismuth silicate glass together with derived samples by replacements of parts of the Bi₂O₃ by SrO, BaO, or PbO. This study aims to justify and compare the spectral and shielding behavior of the studied glasses containing heavy metal ions towards gamma irradiation. The study also aims to measure or calculate the optical energy band gap of these glasses. The replacements of parts of Bi₂O₃ by SrO, BaO or PbO caused some changes within the optical and infrared absorption spectra due to the different housing positions and physical properties of the respective divalent Sr2+, Ba2+, Pb2+ ions. The stability of both the optical and infrared spectra of the studied bismuth silicate glass and related samples towards gamma irradiation confirm some shielding behavior of the studied glasses and their suitability as radiation shielding candidates.     

ESR Study of Devitrification Processes

The radiation-induced ESR centers in glasses with different Ti concentrations were studied to elucidate crystallization processes in the glass. The parameters of the induced ESR absorption associated with the T ₂ center were investigated systematically as a function of heat treatment. The induced T ₂ centers in the glasses containing small concentrations of Ti characteristically decreased in intensity as nucleation began and disappeared completely in devitrified samples. A mechanism is proposed for the destruction of the T ₂ center as nucleation proceeds to crystallization. Supporting X-ray diffraction evidence is given. The systematic decrease in the ESR intensity of this radiation-induced center provides a means of monitoring devitrification processes in glasses.     

Spectroscopic Inquiry of the Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-role in Binary Sodium Borate,Sodium Silicate and Sodium Phosphate Glasses and Effects of Gamma Irradiation

Optical absorption spectral investigations have been carried out on Fe³⁺ ions doped sodium borate, sodium silicate and sodium phosphate glasses before and after gamma irradiation. The UV-visible absorption spectrum exhibits bands characteristic of Fe³⁺ ions coordination in each system. Interesting aspects of FT-IR spectra were found, and this gives information about the structure changes in the constituent units of these glass systems as a function of Fe₂O₃ concentration. All glasses reveal characteristic absorption bands due to the addition of different ratios of iron which explain the state of iron in each system in terms of its valence and coordination number. Results indicate that iron favors a higher oxidation state (tetrahedral coordination) in the case of sodium silicate glasses. The doping with progressive Fe₂O₃ additions (0.5?7.5 %) has some effect on the number and position of the characteristic bands due to formation of FeO₄ groups. The IR absorption spectra after irradiation reveal limited changes in the intensity which can be correlated with minor changes in bond angles and /or bond lengths within the structural units by irradiation.     

Controlled nano-crystallization of IR frequency-doubling Cd4GeS6 crystal in chalcogenide glass

Crystallization of IR frequency-doubling nanocrystals in chalcogenide glasses is a promising approach to achieve novel nonlinear optical materials. However, controllable glass crystallization remains challenging. In this study, IR-transparent chalcogenide glass-ceramics containing novel Cd₄GeS₆ IR frequency-doubling nanocrystals (about 60-80 nm) are fabricated through controlled nano-crystallization. Nanocrystalline structure of the Cd₄GeS₆ nano-crystallized glass-ceramics is investigated in detail through X-ray diffractometer, field emission scanning electron microscope, and Raman scattering techniques. The structural similarity of [Cd₄GeS₆] polyhedron in the network structure of as-prepared glass is found to be responsible for the nucleation of Cd₄GeS₆ crystal. A unique microstructure of Cd₄GeS₆ nanocrystals embedded GeS₂ phase-separated structure is discovered in samples thermally treated at high temperatures (370°C and 380°C). This study would not only shed more light on glass crystallization mechanism but also provide a feasible approach for the design and fabrication of new IR frequency-doubling materials through glass crystallization.     

Corrosion and Infrared Study of Some γ-Irradiated Lead-Phosphate Glasses Doped with MoO3

In this study we compared the effect of three different concentrations of MoO₃ on the corrosion of sodium phosphate glass containing lead and aluminum oxides to develop its durability. The corrosion was studied in deionized water and acidic solution of 0.1 N HCl. The dissolution mechanism is interpreted depending on the glass weight loss versus time and change in the glass surface. MoO₃ had a stabilizing effect on the glass, causing a decrease in the glass dissolution rate. Acidic medium was found to strongly enhance the glass dissolution. The pH decrease in water with increase in acidic solution gives evidence of the release of some phosphorous ions to form phosphoric acid. The consequent enhancement of the glass durability was influenced by the presence of MoO₃ and showed a remarkable advance by doping with 3 wt% of MoO₃. FT-infrared absorption spectra of the studied glasses show IR vibrational bands due to phosphate groups mainly of the metaphosphate and pyrophosphate units together with the sharing and interference of IR vibrations due to Pb–O bonds. Gamma irradiation produces a minor effect on the IR spectra, and enhances the base glass durability at the beginning of the corrosion process, which can be related to the shielding behavior of the high lead glass. However, glass containing 3% MoO₃ has the best durability and is the least affected by irradiation. The glass durability corresponding to its structure is verified by IR spectroscopy.

     

‘Optical and FT Infrared Absorption Spectra of Soda Lime Silicate Glasses Containing nano Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and Effects of Gamma Irradiation

The optical absorption spectra of undoped soda lime silicate glass together with two glasses doped with either (1 % nano Fe₂O₃ ) or with both (1 % Nano Fe₂O₃ + 5 % cement dust) have been measured from 200 to 2400 nm before and after gamma irradiation with a dose of 8 Mrad. The undoped glass reveals strong UV absorption with two distinct peaks which are attributed trace ferric iron ions present as impurity. Upon gamma irradiation , this base glass exhibits three peaks at 240,310 and 340 nm and the resolution of an induced broad visible band centered at 530 nm. The two doped glasses show an additional small visible band at about 440 nm and followed by a very broad band centered at 1050 nm. Upon gamma irradiation, the two doped samples reveal the decrease of the intensities of the spectrum. The two additional bands are related to ferric (Fe⁺³) ions to the band at (440 nm) while and the broad band at 1050 nm is due to ferrous iron (Fe⁺²) ions. The decrease of the intensities of the UV-visible spectrum upon irradiation can be related to of capturing freed electrons during irradiation . Infrared spectra of the glasses reveal repetitive characteristic absorption bands of silicate groups including bending modes of Si–O–Si or O–Si–O, symmetric stretching , antisymmetric stretching and some other peaks due to carbonate , molecular water , SiOH vibrations . Upon gamma irradiation, the IR spectra reveal a small change in the base spectrum while the IR spectra of the two doped glasses remain unchanged. The change of the IR spectrum of the base glass is related to suggested changes in the bond angles or bond lengths of the mid band structural units. The doped glasses show resistance to gamma irradiation because the nano Fe₂O₃ can capture released electrons and positive holes.     

Unveiling crystallization mechanism for controlling nanocrystalline structure in glasses

Controlling nanocrystalline structure in glasses renders the exploration of new composite multiphase (glass-ceramic) materials with novel functionalities that determined by the precipitated nanocrystals and residual glassy matrix. Previous microstructural investigation of glass-ceramics focused only on one aspect of nanocrystalline structures, e.g., nano-polycrystalline or single nanocrystalline. The recognition of the microscopic mechanism of nanostructure formation in glasses is absent. Here, we use advanced microscopic techniques to show the formation of different nanocrystalline structures composed of nano-polycrystals and single nanocrystals in 80GeS₂·20In₂S₃ and 72.5GeS₂·14.5Sb₂S₃·13RbCl glasses, respectively. Crystallization mechanism for controlling the nanocrystalline structure in glasses was revealed to depend on whether the glass network former participates in crystallization process. The results may shed light not only on glass crystallization mechanism, but also on the fundamental nature of the network structure of chalcogenide glasses.