Low-temperature luminescence of lead silicate glass (original) (raw)
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Thermoluminescence kinetic study of binary lead-silicate glasses
2009
This paper describes a detailed experimental study of the thermoluminescence (TL) properties of four binary lead-silicate glasses, with PbO concentrations ranging from 32% to 62% in mole percent. The TL glow peaks between room temperature and 300 1C were analyzed using a systematic thermal cleaning technique. The T max -T stop and E-T stop methods of analysis were used to identify the number of peaks under the glow curves, and to obtain the activation energy E for each TL trap. A computerized glow curve fitting analysis is used to fit the experimental data to four first-order peaks with maxima at temperatures of 54, 80, 110 and 210 1C, as measured with a heating rate of 2 1C/s. The kinetic parameters of the glow-peak at 210 1C were confirmed by using phosphorescence decay methods of analysis. The TL traps associated with the low-temperature TL peak at 54 1C are found to depend strongly on the PbO concentration of the samples, while the higher-temperature TL peaks show a behavior independent of the PbO concentration. The activation energy E and frequency factor s of the low-temperature TL trap associated with the peak at 54 1C are consistent with a trap involving a delocalized transition through the conduction band. However, the activation energies and frequency factors for the higher-temperature TL traps are consistent with traps involving localized transitions via an excited state below the conduction band. The data suggest that these higher-temperature TL traps are associated with the common silicate matrix in these binary silicate glasses.
Journal of Non-Crystalline Solids, 2001
In this paper, we report the excitation energy dependence of the 2.7 and 4.3 eV photoluminescence (PL) bands in oxygen de®cient silica glass at low temperature ($20 K). The increase or decrease of the PL intensity at low temperatures is dierent for dierent exciting light wavelengths. The PL intensity tended to decrease with low temperatures when the excitation was near the upper and lower end of the excited level. The peak energy of the excitation spectrum increases with cooling. These results indicate that the change in excitation level with cooling is associated with the lowtemperature dependence of light emission. Thermal motion is suppressed, when the sample temperature is lowered, and the energy-width of the excited level decreases, i.e., the light emission probability decreases (the emission intensity decreases), when near the upper and lower end of the excitation level. These phenomena were observed in the lowtemperature dependence of the 4.3 eV emission intensity. Ó
Localized states of silicon dioxide, sodium and lead silicate glasses
Journal of Non-Crystalline Solids, 1990
Luminescent methods were used for the study. In silica the electronic excitations are similar to those in quartz, but the excitons are localized. The self-trapped excitons in both materials are similar; however in glass some of them are strongly quenched. The same quenching is common for localized states luminescence in sodium and lead silicate glass. The non-zero luminescence polarization in these glasses is a strong proof for the presence of localized states in the fundamental absorption range of complex silicates.
Luminescence of localized states in silicon dioxide glass. A short review
Journal of Non-Crystalline Solids, 2011
The target is the description of the properties of localized states in silica glass, which relate to aspects of shortto-intermediate-range order. It has been observed that laser light interaction with localized states of silica glass leads to the creation of luminescence centers. Created luminescence centers, excited with laser light, provide intra-center luminescence of oxygen deficient centers (ODC) comprising a blue band at 2.7 eV and a UV band at 4.4 eV. Structurally, these ODCs are understood to comprise twofold-coordinated silicons that are commonly part of some larger local structure, and their luminescence bands can be suppressed by reaction with chlorine or hydrogen. Beside these processes laser light can give rise to charge separation. Recombination of well separated electrons and holes leads to recombination luminescence, which is similar to intra-center process luminescence but with greatly suppressed UV emission relative to the blue band and longer duration decay times. Evidence has been given that center of recombination at ODC sites involves an electron trap at the defect, whereas the hole is created as self-trapped holes (STHs) centers. Recombination results in the localized state recovering its initial state. Studies of temperature dependences of recombination luminescence intensity and decay show that intensive changes in these parameters take place in the known range of temperatures of STH liberation. Decrease of measured intra-center luminescence duration with increasing temperature is accompanied by less rapid decrease of recombination luminescence intensity. In the temperature range~300 to 450 K, the blue luminescence intensity actually grows with heating, with little change in the decay time constant. As a rule, luminescence decay curves are non-exponential well described with stretched exponential function, showing first order fractal-kinetics. It is argued that discovered localized states of silica glass are connected with structure other than tetrahedrons. In dense silicon dioxide crystal with rutile structure (stishovite) luminescence similar to ODC luminescence of silica glass has been found.
Structure-property correlations in lead silicate glasses and crystalline phases
2013
Lead silicate glasses containing 40-65 mol% of PbO were prepared at two meltquenching rates and characterized by X-ray diffraction, UV-Visible absorption spectroscopy, density, microhardness, thermo-mechanical analysis, differential scanning calorimetry and Raman scattering studies. On increasing the PbO concentration, density increases, glass transition temperature decreases and the optical absorption edge shifts towards longer wavelength. An intense optical absorption band was observed just below the absorption edge in glasses with 55 mol% and higher concentration of PbO. Dilatometric measurements show an unusual property that glasses do not show any abrupt increase in volume near the glass transition temperature but transform directly into the liquid state. Raman spectroscopy confirmed that the concentration of SiO 4 tetrahedra containing one or more NBOs increase with PbO mol%. Devitrification studies on lead silicate glasses found that samples with 40-45 mol% of PbO do not crystallize, whereas samples with higher PbO concentration produce multiple crystalline phases like PbSiO 3 , Pb 33 Si 24 O 81 , Pb 2 SiO 4 and Pb 3 Si 2 O 7 on heat treatment.
Stationary and nonstationary absorption in lead silicate glasses with short-range order inversion
Optical Materials, 2011
The methods of stationary and pulsed absorption spectroscopy were used to study the optical properties of xPbOÁ(1-x)SiO 2 glasses produced by cooling of a molten mixture of chemically pure oxides. The spectral dependence of the absorption in the range of the short-wavelength edge obeys the Urbach rule. As the PbO concentration increases, a red shift of the optical transparency cutoff is observed. At x = 0.45-0.50 the amorphous matrix undergoes a structural inversion, which is due to a transition from a silicate to a lead-oxygen glass-forming network. This transition shows up as an abrupt change in the type of optical transitions, the width of the optical gap E g , and the Urbach energy E U. The short-range order inversion in the glass is accompanied by an increase in the atomic correlation radius R 0 characterizing the size of the medium-range order in the system. It was found empirically that R 0 has a linear relationship with a continuum-disorder parameter E U. It was found that pulsed electron irradiation produces short-lived color centers, which absorb at 1.65 and 2.30 eV. The relaxation of unstable absorption centers is characterized by microsecond kinetics. The nature of unstable absorption centers and their relationship with a short-range order inversion and the structure function of lead atoms have been discussed. The kinetic dependences have been interpreted in the context of a mechanism responsible for diffusion-controlled tunneling recombination of radiationinduced electronic and hole states of the matrix.
Structural Transitions of Silicate Nanocrystals in the Glass
American Journal of Materials Science, 2012
The temperature dependences of resistivity and thermopower measurements reveal that nanocrystals of silicates in lead-silicate glass of various compositions undergo structural transitions in the temperature range of 800-1000 K. The diameter of these nanocrystals estimated from Scherrer's formula is about 0.8-1.6 nm and each nanocrystal consists of 8-64 unit cells. Structure transitions are detected as sharply maxima of resistivity ρ and thermopower S at temperature T = 800-100 K. Lead-silicate glass was doped by RuO 2 up to 16 weight% to facilitate the measurements of the ρ and the S. The doped lead-silicate glass has a metal-like behavior at the room temperature: the temperature dependences ρ(T) and S(T) are very slow, the value of the S is typical for metals (few and tens of μV/K). Beyond the maximum of the resistance (temperature T > 1000 K) doped lead-silicate glass turns into typical semiconductor having energy gap about 0.05-1.5 eV depending on the composition of the glass. Anomalous thermal expansion of the RuO 2 relict crystals is detected at the temperatures of 800-1000 K as well.
Sub-band-gap-excited luminescence of localized states in SiO2–Si and SiO2–Al glasses
Journal of Non-Crystalline Solids, 2010
Silica glass samples doped with extra silicon (SiO 2 -Si: artificial oxygen deficiency) and with aluminum (SiO 2 -Al: Al-doped without accompanying alkali ions) were studied. The luminescence properties of these two samples are compared in the range of temperature 15-290 K under excitation of ArF excimer laser (193 nm). In both samples the luminescence of oxygen deficient centers (ODCs) is detected, i.e., emission bands in the blue at 440 nm and the UV at 280 nm. Cooling of the both samples led to strong increases of luminescence intensity down to 80 K with much smaller increases for still lower temperatures. At 290 K in SiO 2 -Si a luminescence similar to that of twofold-coordinated silicons in stoichiometric silica glasses was detected, i.e., displaying exponential decay of emission bands in the blue (s = 10.3 ms) and UV (s = 4.5 ns). In both samples emission at 440 nm occurs in times shorter that $400 ls, according to a non-exponential decay law. These decay times are much faster than the 10.3 ms exponential decay typical of the twofold-coordinated silicon center in pure undoped silica. Conversely, the decay of the UV band possesses an additional decay ranging from 2 to 5 ls, that is much slower than 4.5 ns typical of lone twofold-coordinated silicons in stoichiometric silica. Prolongation of the decay time of UV emission can only be explained in terms of electron-hole recombination processes. Moreover, the observed diminishing of the luminescence intensity concomitant with acceleration of decay times with increasing temperature above 90 K is found to be correlated with thermally activated recombination of self-trapped holes in pure silica [D.L. Griscom, J. Non-Cryst. Solids 149 (1992) 137]. It is concluded that the ArF-laser induced electronic processes of recombination luminescence in SiO 2 -Si (and SiO 2 -Al) are related to trapping of an electron on in a localized state related to oxygen deficiency (or to an Al in the SiO 2 network) and nearby trapping of a hole on a normal bridging oxygen, forming an STH.
Electronic states spectrum for lead silicate glasses with different short-range order structures
Journal of Non-Crystalline Solids, 1991
Molecular orbital (MO) linear combination of atomic orbitals (LCAO) simulation of the electronic states spectra of PbO-SiO 2 glass with different structures of short-range order is performed. It is determined that superposing of 'almost free' Pb 2+ ion levels on silicon-oxygen spectrum takes place in low-lead glass, whereas high-lead glasses are characterized by mixing of Pb and O atoms valency states. Density-of-states peaks in X-ray photoelectron spectra and optical Pb6s ~ Pb6p transition with 5.2-3.0 eV energy as a function of Pb structural role are identified. The most probable radiation centers in PbO-SiO 2 glasses are the analogues of known E-and H + centers formed on the band energies edges as a result of electron-hole localization-Si-O-...Pb 2+ fragments.
Luminescence of silicon Dioxide - silica glass, α-quartz and stishovite
2011
This paper compares the luminescence of different modifications of silicon dioxide -silica glass, α-quartz crystal and dense octahedron structured stishovite crystal. Under x-ray irradiation of pure silica glass and pure α-quartz crystal, only the luminescence of self-trapped exciton (STE) is detected, excitable only in the range of intrinsic absorption. No STE luminescence was detected in stishovite since, even though its luminescence is excitable below the optical gap, it could not be ascribed to a self-trapped exciton. Under ArF laser excitation of pure α-quartz crystal, luminescence of a self-trapped exciton was detected under two-photon excitation. In silica glass and stishovite mono crystal, we spectrally detected mutually similar luminescences under single-photon excitation of ArF laser. In silica glass, the luminescence of an oxygen deficient center is presented by the so-called twofold coordinated silicon center (L.N. Skuja et al., Solid State Commun. 50, 1069). This center is modified with an unknown surrounding or localized states of silica glass (A.N. Trukhin et al., J. Non-Cryst. Solids 248, 40 (1999)). In stishovite, that same luminescence was ascribed to some defect existing after crystal growth. For α-quartz crystal, similar to silica and stishovite, luminescence could be obtained only by irradiation with a lattice damaging source such as a dense electron beam at a temperature below 80 K, as well as by neutron or γ-irradiation at 290 K. In spite of a similarity in the luminescence of these three materials (silica glass, stishovite mono crystal and irradiated α-quartz crystal), there are differences that can be explained by the specific characteristics of these materials. In particular, the nature of luminescence excited in the transparency range of stishovite is ascribed to a defect existing in the crystal after-growth. A similarity between stishovite luminescence and that of oxygen-deficient silica glass and radiation induced luminescence of α-quartz crystal presumes a similar nature of the centers in those materials.