[en] An application of the glow rate technique (GRT) for analysis of the parameters of thermostimulated decay of colour centres is presented using the data on the decay of radiation defects in LiBaF₃:Fe crystals created by X rays at 300 K. The GRT offers a procedure for evaluation of the mean activation energy as a function of temperature in the case of arbitrary thermostimulated relaxation kinetics represented by the trap distribution function. The experimental procedure involves at least two subsequent measurements of thermostimulated decay kinetics at different heating rates. It is shown that the decay of the F type centres is governed by interaction of mobile anion vacancies with F_A and F centres, leading to both the hopping migration and recombination of F centres and the thermoactivated dissociation of the F_A centres. (author)

[en] The glow rate technique (GRT) is the extension of the known heating rate method to the full glow curve. The GRT like the fractional glow technique (FGT) offers a procedure for evaluation of the mean activation energy as a function of temperature in the case of arbitrary thermostimulated relaxation kinetics represented by trap distribution function. The experimental procedure involves at least two subsequent measurements of thermostimulated recombination kinetics at different heating rates. The extension of the GRT to the direct measurements of thermostimulated bleaching of the radiation-induced color centers is presented. The experimental procedure involves measurements of the decay of radiation-induced absorption spectra of color centers in preliminary irradiated materials during linear heating. Procedure for evaluation of the trap energy and frequency factor spectrum is considered in the paper. Results of the application of GRT for analysis of the parameters of thermostimulated decay of color centers are presented in the case of decay of the radiation-induced defects in LiBaF₃ crystals irradiated by X-rays. It is shown that decay of F-type centers occurs in two steps, the activation energy slightly decreasing from 0.660±0.003 eV in the first step (300-370 K) to 0.615±0.003 eV (400-480 K) in the second step

[en] At present in slow neutron imaging an active layer of an imaging plate IP contains a mixture of storage phosphors, usually BaFBr:Eu²⁺ used for imaging of X-rays, and a neutron converter material, usually Gd₂O₃, LiF. A novel Li-containing luminescent material perspective for a direct neutron conversion and storage is discussed. Irradiation of LiBaF₃ crystals results in generation of Frenkel defect pairs and creation of F-type centres responsible for three absorption bands in UV-and visible spectral region. Because photo-stimulation in each of these absorption bands leads to bleaching of induced absorption, the F-type colour centres are convenient for storage of radiation dose. Photo-stimulated decay of F-centres causes recombination luminescence of impurity centres. Thermoactivated decay of F-type centres is governed by ionic process. The thermal stability of F-centres at RT and consequent material storage characteristics can be improved by doping of the LiBaF₃ with heterovalent oxygen impurities. The obtained radiation energy storage, photo- and thermostimulated read-out characteristics justify that LiBaF₃ is a suitable active media for imaging of slow neutrons

[en] Ionic and ion diffusion-controlled thermally stimulated relaxation (TSR) processes in CaF₂, BaF₂ and LiBaF₃ crystals (X-ray irradiated at 290 K) have been investigated by means of ionic conductivity and the correlated ionic thermally stimulated depolarisation current (TSDC), and radiation-induced optical absorption band thermal bleaching techniques at 290-650 K. It was found that under a DC field fluorides store large ionic space-charge. In CaF₂, BaF₂ and LiBaF₃, by using the ionic TSDC technique we were able to detect a series of the interstitial anion and/or anion vacancy delocalisation stages in the extrinsic ionic conductivity region. At least 4-6 wide and overlapping ionic TSDC ''peaks'' were observed. The activation energy values of the ionic conductivity and ionic TSDC coincide, or are very close: 1.313±0.002 and 1.27±0.02 eV for CaF₂, 1.040±0.002 and 1.00±0.02 eV for BaF₂ and 0.91±0.04 and 0.780±0.013 eV for LiBaF₃, respectively. The correlated data of the ionic TSDC and thermal bleaching (of the F band and other radiation-induced absorption bands) suggest that above RT ion diffusion-controlled TSR processes take place in CaF₂, BaF₂ and LiBaF₃ crystals. These processes are initiated and controlled by the anion defect thermal detrapping, migration and interaction with the trapped charges

[en] We reported on the recombination processes determined by the release of electrons from defects connected with the dosimetric 430 K thermostimulated luminescence (TSL) peak as well as with the 260 K TSL peak. These TSL peaks appear in thermochemically reduced α-Al₂O₃ crystals containing hydrogen and emission of these TSL peaks corresponds to luminescence of the F-center. The X-ray exposure or UV excitation in the absorption band of F-centers at 6.0 eV of reduced α-Al₂O₃ crystals doped with acceptor impurities results in the appearance of a broad anisotropic complex absorption band in the spectral region 2.5-3.5 eV and in the appearance of a predominant TSL peak at 430 K. Above 430 K the above-mentioned broad absorption band disappears. Optical bleaching of the 2.5-3.5 eV band is accompanied by the disappearance of the 430 K TSL peak and results in F-center emission. The X-ray or UV excitation of reduced α-Al₂O₃ crystals with donor-type impurities results in the appearance of an anisotropic absorption band at 4.2 eV and the appearance of a dominant TSL peak at 260 K. Above 260 K the 4.2 eV absorption disappears and photostimulated luminescence (PSL) of the F-center recombination luminescence in the 4.2 eV region is no longer observed. Optical bleaching of the 4.2 eV absorption band is accompanied by the disappearance of the 260 K TSL peak. The successful use of reduced α-Al₂O₃ in dosimetry needs the optimization of the concentration of all components (acceptors, hydrogen, intrinsic defects) involved in the thermo- and photostimulated processes. (Author)

[en] The creation of radiation defects in LiBaF₃ crystals at 10 K and the processes of their thermostimulated recombination are investigated. The methods of optical absorption, thermal bleaching of color centers, thermostimulated luminescence and fractional glow technique are used. The radiation defects anneal in a multi-stage process accompanied with thermo-luminescence at 20, 46, 105, 130, 170, 210 and 270 K. Differences in the optical absorption spectra measured before and after the TSL peaks are obtained and recombination parameters are determined. The TSL peak at 20 K arises from the delocalization of H-centers. The presence of two TSL peaks related to V_K-centers at 105 and 130 K indicates that 60 deg. and 90 deg. migration hops occur

[en] We investigated electron paramagnetic resonance (EPR) angular dependencies, recombination afterglow and thermostimulated luminescence of undoped LiBaF₃ crystals, X-irradiated at low temperatures. EPR parameters of the F₂^- molecule oriented along the [1 1 0] direction have been obtained. Based on the value of the g-shift Δg=g_{perpendicular} g_II=0.02, characteristic for the V_K-centres in similar perovskites, we propose that we indeed observed the V_K-centres, not the H-centres. X-irradiation below 170 K results in creation of a long-time temperature-independent afterglow due to the tunnelling recombination between close electron and hole centres. The F-type electron centres and the V_K as well as probably O^2- centres are proposed to be the tunnelling recombination partners, responsible for the 4.1 and 3.15 eV luminescence bands, respectively

[en] Full text: Creation of radiation defects in LiF, BaF₂ and LiBaF₃ crystals and their thermostimulated recombination process are investigated. Methods of optical absorption, thermal bleaching of colour centres, thermostimulated luminescence (TSL) and fractional glow technique are used. The radiation defects in LiBaF₃ annealed in multi stage process accompanied with thermo-luminescence at 20, 46, 105, 130, 170, 210 and 270 K. Possible parameters of recombination partners are determinate by the difference of optical absorption spectra measured before and after TSL peaks. These processes are to be compared to similar processes in LiF and BaF₂. The TSL peaks at 105 K and 130 K in LiBaF₃ are governed by thermo activated migration-tunnelling recombination of self-trapped holes. Presence of two TSL peaks of V_k-centres at 105 and 130 K indicates that the 60⁰ and the 90⁰ migration hops occur. The expected absorption bands of V_k - centres are at 3.2 and 4.3 eV

[en] Thermo- and optically stimulated processes are studied in reduced α-Al₂O₃ excited by X rays or UV light. It is shown that the 430 K TL peak and OSL band at 2.7 eV is caused by release of electrons from traps followed by recombination mainly at F⁺ cntres and resulting in F centre emission. Traps responsible for the composite 430 K TL peak and induced 2.7 eV absorption band are caused by several kinds of defects of an electronic nature. Production of free electrons by selective UV excitation in the region of the absorption of F centres results in effective filing of all kinds of traps responsible for the 430 K TL peak, whereas free electrons and holes produced by X ray excitation competitively recombine via various localised electronic states, which results in lowered efficiency of the accumulation of the light sum and selective filling of different kinds of traps, responsible for the 430 K TL peak. (author)

[en] TSL properties of the DTG-4 LiF:Mg,Ti dependent on the annealing treatments in the temperature region 350-500 K are examined by the fractional glow technique and by the decay of the optical absorption spectra. Association-dissociation reactions involving Mg-V_c dipoles and anion vacancies are discussed. Increased observed values of the mean TSL activation energies and the mean frequency factors, the latter sufficiently exceeding the optical phonon frequency, are explained as arising from the change of the concentration of the moving defects with temperature. These moving defects perturb the electronic traps and lower the activation energy of electron release in approaching the trap. The origin of the moving ionic defects is considered. (author)