Thermally stimulated luminescence of dosimetric α-Al2O3 crystals

The results of experimental and theoretical research on thermally stimulated luminescence (TSL) of dosimetric crystals based on anion-defect corundum are systematized. It is shown that all of actually observed features — the dependence of the TSL yield on the heating rate, the dependence of the temperature position of the TSL peak and its shape on the irradiation dose and the heating rate, and the drop in average activation energy within a dosimetric peak — are due to a single process: quenching of the luminescence ofF centers. Evidence is given for a relationship between quenching and the presence of oxygen vacancies of thermochemical or radiative origin. Unusual behavior of Cr³⁺ ions during thermoluminescence is found. It is suggested that the TSL peak in anion-defect corundum is due to a complex defect formed by oxygen vacancies in various charged states, chromium ions, and possibly the ions of other transition metals. Ural State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 145–161, November, 1996.     

On the role of hole trapping centers in the interactive mechanism of the trap interaction in anion-defect alumina single crystals

The effect of deep hole traps on the intensity and shape of the dosimetric peak of thermoluminescence (TL) has been studied at 450 K in anion-defect alumina single crystals. It has been shown that filling of deep hole centers leads to a decrease in the sensitivity to radiation of crystals with a small half-width of the TL peak and has no effect on the sensitivity of crystals with a broadened peak. It has been assumed that traps responsible for the TL dosimetric peak broadening are of hole nature, which can be caused by the presence of Ti3+ ions in the corundum lattice. The results obtained have been interpreted within the modified model of the interactive system of traps.     

Photosensitive defects in silica layers implanted with germanium ions

Ge-implanted silica layers have been investigated by high-power pulsed synchrotron-photoluminescence (PL), photoluminescence excitation spectroscopy (PLE), and optically stimulated electron emission (OSEE) with respect to association of excitation and absorption bands to respective emission bands and lifetimes of excited defect states. In this way singlet-singlet (4.35 eV) and triplet-singlet (3.18 eV) radiative transitions from excited states of oxygen-deficient centers (ODC) in Ge-doped silica glass are characterized by their absorption and emission bands as well as their lifetimes. The main channel for non-radiative relaxation of photoexcitation is electron emission by the OSEE effect. The OSEE shows non-radiative transitions of surface and bulk E′-centers found with concentrations of (2.7-3.4) × 10¹² cm⁻² and (2-4) × 10¹⁶ cm⁻³, respectively.     

Spectroscopic characteristics of anionic centers in α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> crystals bombarded by Cu<Superscript>+</Superscript> and Ti<Superscript>+</Superscript> ions

We have studied the effect of bombardment by Cu⁺ and Ti⁺ ions with energy 30 keV on the optical absorption and luminescence of F centers in oxygen-deficient aluminum oxide. We have shown that in the induced optical absorption spectra there are six components of gaussian shape, which can be assigned to absorption bands of F⁺, F², and F₂⁺ centers. We have established that bombardment of the samples by ion beams has a weak effect on the thermoluminescence parameters in the 3.0 eV and 2.4 eV bands, while in the 3.8 eV luminescence band for F⁺ centers, the thermoluminescent response increases considerably. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 422–424, May–June, 2008.     

X-ray emission and photoluminescence spectroscopy of nanostructured silica with implanted copper ions

Quartz glass samples and compacted SiO₂ nanopowders have been studied by x-ray emission (CuL _{2, 3} transition 3d4s → 2p _{1/2, 3/2}) and photoluminescence spectroscopy following pulsed Cu⁺ ion implantation (energy, 30 keV; pulse current up to 0.5 A; pulse duration, 400 μs; irradiation doses, 10¹⁵, 10¹⁶, and 2 × 10¹⁷ cm^?2). It has been established that ion irradiation gives rise to the formation of glassy and compacted SiO₂ samples of nanosized metallic and oxide phases in the structure. An analysis of CuL x-ray emission spectra has shown that copper nanoparticles are thermodynamically metastable and chemically active because ion beam bombardment transfers them readily to the oxide form. This results from the radiation-stimulated fracture of regular Si-O-Si bonds in amorphous SiO₂ and the formation of defective Si-Si bonds, followed by capture of oxygen by copper atoms. The enhanced degree of oxidation of copper ions in SiO₂ nanostructured pellets can be reduced by coimplantation and thermal annealing. Optical spectroscopy studies suggest that, in glasses and SiO₂ nanostructured pellets, there exist metallic Cu _n ⁰ nanoclusters, which at low temperatures exhibit quantum-confined photoluminescence with a characteristic stepped excitation spectrum.     

Electron-emission activity of defects in surface layers of crystalline and vitreous silica

This paper deals with the photoemission activity of radiation defects in crystalline and vitreous silica. Spectral and kinetic parameters and the concentration of defects in the surface layer and the bulk of the material were determined. Some features of the distribution of radiation-induced defects along the depth of samples having different degrees of order were analyzed. Regularities of relaxation of excited states of emission centers suggested that thermally activated processes were involved in the release of electrons.     

Nanophosphors and outlooks for their use in ionizing radiation detection

The fundamental properties of nanophosphors determined by their structural state are discussed. The influence of a high concentration of surface trapping centers and quantum confinement effect on the nanophosphor luminescence characteristics is noted. These features determine some new properties, which are important for radiation detection. They include the increase in the luminescence yield under high-dose irradiation and improvement of radiation resistance. The luminescence and dosimetric properties of nanophosphors of different compositions are described. It is noted that nanophosphors show promise as high-dose detectors of ionizing radiation.     

Luminescent vacuum ultraviolet spectroscopy of Cr3+ ions in nanostructured aluminum oxide

Impurity Cr³⁺ centers in submicron and nanostructured Al₂O₃ crystals of different phase compositions at temperatures of 300 and 7.5 K were studied by a luminescent vacuum ultraviolet (VUV) spectroscopy method. Photoluminescence (PL) spectra and the energies of ²E, ⁴T₂, and ⁴T₁ excited states of Cr³⁺ ion depend on the type of crystalline samples phase. The PL excitation spectrum of R-line in α-Al₂O₃ nanoscale crystals is formed by intracenter transitions (2.5–5.5 eV region), by charge transfer band (6.9 eV) and by effective formation of impurity-bound excitons (9.0 eV region). Such impurity-bound excitons correspond to O₂p→Al₃s electron transition in surroundings of an impurity Cr³⁺ center. The efficiency of impurity-bound excitons formation decreases with the increase of the grain size above 100 nm. The size dependence is noticeably shown in PL excitation spectra in VUV region. Excitons bound to impurity centers do not appear in nanostructured δ+θ-Al₂O₃ crystals. The effect of the electron excitation multiplication is observed distinctly in nanostrucured α-Al₂O₃ at an excitation energy above 19 eV (more than 2E_g).     

Pulsed cathodoluminescence of nanoscale aluminum oxide with different phase compositions

The methods of pulsed cathodoluminescence have been used to study compacted powders and ceramics containing different phases of aluminum oxide. An intensive luminescence of the samples under study in the visible, NIR, and UV regions of the spectrum has been found. The luminescence bands are very broad and include a few components. The number of the bands depends on the phase composition of the samples. The oxygen vacancies, which capture one or two electrons, produce luminescence centers in the near UV region. The most probable in the visible region is the luminescence of aggregate defects, impurities, and surface centers.