Search results for "absorption."
showing 10 items of 2682 documents
Relaxation of electronic excitations in strontium titanate
2002
The transient absorption spectra and kinetics were studied for undoped, lead doped and high purity SrTiO 3 single crystals. The pulsed electron beam induced transient absorption is studied in all crystals. The strong absorption at 0.8 v eV was observed only in high purity SrTiO 3 . This absorption is suggested to arise from intrinsic electron polaron. The bound electron polarons are likely responsible for absorption band at 1.4 v eV. The main luminescence band under excitation pulse is observed at 2.75 v eV. The luminescence decay is faster than that of transient absorption.
The experimental observation of the potential barrier for self-trapped exciton decay into F-H pair in KCl-Na crystals
1995
Abstract The optical absorption induced by the electron pulse irradiation of Na+ doped KCl has been measured. Transient optical absorption band of FA centers was observed at 80 K (LNT). The temperature dependence of FA center formation was studied. It is proposed that the obtained activation energy originates from the potential barrier between the STE perturbed by the cation impurity and the nearest neighbour FA-H pair. The mechanism of the suppression of the defect formation by the monovalent cation impurity in alkali halide crystals is discussed.
ODEPR of indium colour centres in the X- irradiated storage phosphor KBr:In
1995
The results of measurements of the magnetic circular dichroism of the optical absorption (MCDA) and optically detected electron paramagnetic resonance (ODEPR) of X-irradiated KBr :In crystals are presented. The MCDA bands and ODEPR parameters of In°(1) centers and In 2+ centres have been measured. The mechanism of the energy storage in KBr :In crystals is found not to be simply the formation of correlated F centre-In 2+ centre pairs as was assumed previously. Considerable similarities to the storage phosphor BaFBr :Eu 2+ were found for the photostimulated emission and read-out properties.
ODMR of cd impurity centers in gg irradiated BaF2crystals
1995
Abstract The magnetic circular dichroism of the optical absorption (MCD), optically detected magnetic resonance (ODMR) as well as ESR and luminescence in Cd- doped BaF2 crystals γ-irradiated at RT were investigated. MCD signals centered at 295 nm, 290 nm and 365 nm are observed, together with corresponding radiation induced optical absorption bands in the same wavelength regions. The ODMR detected in all these bands is caused by hyperfine (hf) interaction of unpaired spin with Cd− nucleus. Three types of different Cd− related defects have been separated: 1) Cd+ c, represented by the MCD of derivative type centered at 295 nm and hf constant ACd = 480 mT, 2) Cd++c -center having lowered symme…
Thermal relaxation of colour centres in LiBaF3crystals
2001
Abstract Processes in LiBaF3 crystals caused by the thermal decay of F-type centres created by X-irradiation at room temperature have been examined. It is shown that the thermal decay of F-type centres results in the formation of two kinds of electron centres peaking at 630 nm and 740 nm differing in thermal stability. Weak TSL intensity, accompanying the decay of F-centres, also observed as well as the low value of the process activation energy suggest that due to the presence of moving anion vacancies a random walk of the F-centres occur. We propose that in course of the random walk of the F-centres both the aggregate F-centres are created and the annihilation with some complementary radi…
Transient color centers in GGG crystals
2002
Electron pulse induced absorption and their decay kinetics have been investigated in samples of GGG crystals with different starting absorption spectra. It is shown that for all samples there appears a wide transient absorption (TA) band with two maxima in the region 14,000-17,000 v cm m 1 and 22,000-26,000 v cm m 1 . TA decay kinetics measurements in 14,000 v cm m 1 and 22,000 v cm m 1 are two-exponential (with half-time order several tens and several hundreds ns). Analyzing the obtained results, we can suppose that low and high energy TA bands are connected with the F + (or O m ) and F transient color centers (TCC) respectively.
Time-resolved spectroscopy of ZnWO4
2001
The luminescence spectra of ZnWO 4 excited by a pulsed electron beam, pulsed nitrogen laser and X-ray are studied. The luminescence decay kinetics are compared with transient absorption relaxation kinetics. Broad band transient absorption spectra are observed and it is shown that the slow decay component (∼14 μs at RT) of the transient absorption matches well with the luminescence decay therefore this absorption is due to the excited state absorption of the luminescence center.
Modelling of point defects in α-AL2O3
1995
Abstract The semiempirical method of the Intermediate Neglect of Differential Overlap (INDO), in the program SYMSYM, has been used for calculations on perfect and imperfect corundum crystals. For the perfect crystal the periodical Large Unit Cell (LUC) model was used while the Molecular Cluster (MC) model was used in defect calculations. By means of the MC model, we have investigated the optical properties of electronic centers (F+, F, F−, FMg, F− Mg) in corundum. Calculated optical properties of these defects are compared with experimental values and new bands are predicted to exist in the absorption spectrum of Mg-doped corundum. The energy levels of F-type and Mg-impurity related centers…
Induced optical absorption and ITS relaxation in LiNbO3
1999
Abstract Electron pulse induced absorption spectra and their decay kinetics have been investigated in LiNbO3 crystals with various Li/Nb ratios rasnging from congruent to stoichiometric composition. It is shown that the absorption spectra, the optical density and the decay kinetics depend on the Li/Nb ratio. The rising front of the induced absorption is too fast to be resolved. The room temperature decay, characterized by the half-lifetime Δt, is faster in the stoichiometric crystal (∼ 750 ns) than in the congrruent crystal (∼ 3.5 μs).
UV and vacuum-UV properties of ge related centers in gamma irradiated silica
2002
Photochemical inhomogeneity in the reduction process of the optical activity related to Ge oxygen deficient point defects in silica, characterized by an absorption band centered at 5.15 v eV and two emission bands centered at 3.2 v eV and 4.3 v eV, have been investigated. We have made a comparative study of the stationary and time dependent photoluminescence under excitation in the UV (5 v eV) and in the vacuum-UV (7.4 v eV) ranges in natural silica samples with native and with n -irradiation bleached optical activity. Our measurements evidence that the same spectral features are observed in the native and in the irradiated samples, but for an intensity reduction in the irradiated ones. Mor…