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.     

Influence of Point Defects in a Surface Layer on the Strength Characteristics of Glasses

The influence of the nature and the concentration of defects in a surface layer on the radiation resistance and the microhardness of silicate glasses is studied by photoemission spectroscopy. The investigation is performed with two types of silicate glasses: the K8 optical glass irradiated with fast electrons and an industrial sheet glass with a thermally polished surface. It is established that the radiation resistance and microhardness of glasses are determined by the content of structural defects of a particular nature. The radiation resistance of the surface of K8 optical glass decreases with an increase in the concentration of radiation E ^– ₄-centers, which are representative of the density of band-tail localized electron states recharged by irradiation. The microhardness of the studied glasses with different treatment of their surface depends linearly on the number of defect centers at the nonbridging and radiation-damaged bridging bonds of the silicon–oxygen network.     

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.     

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.     

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.     

Radiation Resistance of Porous Glasses

The sintering and evaporation of porous glasses under exposure to CO₂ laser radiation are investigated. It is demonstrated that the resistance of porous glasses to middle-IR laser radiation depends on the conditions of their preparation. The threshold radiation power densities necessary for sintering porous glasses of different compositions are obtained. The optical breakdown in porous glasses is studied. The resistance to near-IR laser radiation is determined for porous glasses prepared under different conditions.     

Spectroscopic Features of Silica Glasses Doped with Tin

The absorption, photoluminescence, and photoluminescence excitation spectra are investigated for tin-doped silica glasses synthesized by different methods. In all the glasses studied, two new centers belonging to the tin dopant in the SiO₂ network are revealed in addition to the well-known oxygen-deficient center with the absorption band at 4.9 eV. One new center is associated with the absorption band at 5.9 eV and the photoluminescence bands at 2.7 and 3.6 eV, whereas the other center is characterized by the absorption band in the range of 4.56 eV and the photoluminescence band at 2.95 eV. Both new centers are identified as oxygen-deficient centers. The latter center is an analog of the centers observed in pure silica glasses synthesized in a nitrogen atmosphere and in germanosilicate glasses prepared by the MCVD and SPCVD methods. It is revealed that the formation of the oxygen-deficient center is one of the main channels of incorporating tin into the SiO₂ network in all tin-containing silica glasses. Consideration is given to the reasons for the lower efficiency of the photodecay of oxygen-deficient centers in the SiO₂ network in tin-containing glasses as compared to that in germanosilicate glasses and for the relatively high efficiency in the formation of the photoinduced refractive index in optical fibers with a core consisting of tin-containing silica glass.     

Gamma-Ray-Induced Coloration in Solids; Application to Glass Systems

General aspects of radiation-induced coloration in solids are discussed. It is considered that the most significant initial effect of the radiation is to produce free electrons and trapped holes in a track. The decay of the track from the initial condition is described in some detail, assuming (a) that the rate of diffusion of electrons from the track is small compared with the rates of other processes and (b) that primary processes which form color centers can be considered to be independent of secondary processes which cause destruction of color centers. A method of calculation is described which gives the concentration of color centers formed at various doses. With plausible assumptions for the parameters, agreement with the data of Schulman et al. on a silver phosphate glass is obtained. The treatment of glasses less simple than the silver phosphate glass is also discussed.     

Color Centers in X-Irradiated Soda-Silica Glasses

The coloration produced by X-irradiation in silicate glasses prepared under oxidizing and reducing conditions was studied. These glasses differed both in the position of the absorption maximums and in the thermal stability of the color centers formed. Maximums were observed at 4.10, 2.70, and 1.96 ev in oxidized glasses and at 2.15 ev in reduced glasses. Additions of a wide variety of cations to the basic glasses modified the coloration produced by X-irradiation. These modifications appeared as new centers or in the enhancement or reduction of coloration produced by X-irradiation in the base glasses. The reduction of ions such as Ce⁴⁺, Eu³⁺, and Yb³⁺ by X-irradiation is observed. Although several of the color centers appeared to be associated with the glass network itself, there was some correlation between the added cations and the coloration of the glass by X-irradiation.     

Local environment of Eu3+ and Tb3+ ions in fluorophosphate glasses of the Ba(PO3)2-MgCaSrBaAl2F14 system

The induced optical absorption and EPR absorption spectra of fluorophosphate glasses of the compositions 40Ba(PO₃)₂ · 60MgCaSrBaAl₂F₁₄ and 5Ba(PO₃)₂ · 95MgCaSrBaAl₂F₁₄ doped with Tb³⁺ and Eu³⁺ ions are investigated within the model of the effective capture volume of free carriers. The concentration dependences of the relative number of radiation centers on the dopant concentration in fluorophosphate glasses are analyzed. It is established that the character of the distribution of dopant ions in glasses depends on the dopant concentration and the structure of the glass. The critical concentrations at which the oxygen local environment of Eu³⁺ or Tb³⁺ ions in the structure of fluorophosphate glasses transforms into a mixed local environment are determined for glasses of the compositions under investigation.     

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.     

Effect of Gamma Radiation on Spectral Transmission of Some Commercial Glasses

An account is given of the effect of gamma radiation on the spectral transmission of certain commercial glasses. Curves are given showing the rate of fading of the coloration produced in these glasses by doses of gamma radiation in the range 10⁴ to 10⁸ rads. The effect on the optical density of some of these glasses by increasing doses of gamma radiation is discussed.     

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.     

Luminescence of modified nonbridging oxygen hole centers in silica and alkali silicate glasses

This paper reports on the results of the investigation of the cathodoluminescence spectra of silica and alkali silicate glasses upon excitation with a pulsed electron beam (energy, 180 keV; current density, 700 A/cm²; pulse duration, 2 ns). The luminescence band observed in the energy range 2.4–2.6 eV is assigned to modified structural defects of the ≡Si-O·/Me ⁺ type. These defects are revealed under high-density electronic excitation and, unlike the known L centers in alkali silicate glasses, are interpreted as a variety of nonbridging oxygen hole centers (defects of the dangling bond type) subjected to a disturbing action of the nearest neighbor alkali metal cations. The cathodoluminescence of similar centers is observed in neutron-irradiated silica glasses with lithium impurities; alkali silicate glasses with Li, Na, and K cations; and glasses in the two-alkali Na-K systems. It is established that the energy of the radiative transition of a modified nonbridging oxygen hole center, namely, ≡Si-O·/Me ⁺, depends on the alkali cation type.     

Photosensitive Mechanism of Dopant-Free, Ultraviolet-Sensitive Calcium Aluminate Glasses

Calcium aluminate glasses show high sensitivity to ultraviolet radiation without the doping of optically active components. A mechanism is proposed to account for their photosensitivity on the basis of the result that the cause of UV-induced coloring is the emergence of two kinds of paramagnetic centers, an aluminum-oxygen hole center (Al-OHC) and an ozonide (O^-₃). In this model, a peroxy linkage connecting tetrahedrally coordinated Al³⁺s and a physically dissolved O₂ molecule are assumed to be present in the glasses as structural defects. On exposure to UV rays, the peroxy linkage homolvtically dissociates into a pair of A1-OHC's by absorbing UV quanta and one of the two resulting A1-OHC's combines with a nearby O₂ to form an ozonide. Experimental evidences substantiating the mechanism are also reported.     

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 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.     

Radiation Dosimeter Glasses

Ionizing radiations produce visible colors in glasses containing certain multiple valence ions. The coloration, which is dependent on the radiation dose, is generally unstable. Combinations of certain ions can produce glasses with sufficient color stability to be used as dosimeters. Combinations of Mn-Fe, Mn-V, and Mn-V-Fe were studied. The response of glasses containing Mn-V-Fe was independent of the intensity of radiation and they may be used in the range between 10⁵ to 2 × 10⁷ roentgens.     

Electronically Conductive Vanadate Glasses for Resistive Plate Chamber Particle Detectors

Particle detectors are constantly being built and refitted with new technology to improve the spatial resolution, radiation hardness, and speed at which the detector can capture particle events. One of the most crucial components of a modern collider experiment is the hadron calorimeter. One of the proposed improvements on future hadron calorimeters is to utilize resistive plate chambers (RPCs). They provide the spatial and energy resolution as well as could provide speed and radiation hardness. RPCs depend on manufacturing electrically conductive glasses that are mechanically strong, durable, radiation resistant, and not ionically conductive. To achieve such requirements, vanadate glasses were developed as alternatives to current prototypes which use soda lime silicate glasses. The conductivity, oxidation states of vanadium, radiation hardness, as well as the prototype performance, were tested on vanadate glasses. The prototype tests show that using 0.40ZnO−0.40TeO₂−0.20V₂O₅ can improve the RPC detector rate up to 100 times.     

Tracer Diffusion and Electrical Conductivity in Sodium-Rubidium Silicon Sulfide Glasses

The tracer diffusion coefficients of ²²Na and ⁸⁶Rb and electrical conductivity were measured in a series of 0.56(Na, Rb)₂S.0.44SiS₂ glasses as a function of the Rb/Na ratio and temperature. The data were used to calculate the Haven ratio as a function of the Rb/Na ratio. The Haven ratio at 149.6°C increases from ∼0.3 in single-alkali glasses to ∼0.80 for intermediate compositions. The results are consistent with a single jump mechanism involving jumps of alkali ions between unoccupied sites. The observed correlation effects arise through interactions between alkali ions and charge-compensating centers in the glass network. The charge-compensating centers are thought to correspond to non-bridging oxygen ions in some oxide glasses and to nonbridging sulfur ions in sodium-rubidium silicon sulfide glasses.