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The emission centers and excited state characteristics of silica glasses implanted with Gd ions were studied by time-resolved pulsed cathodoluminescence. It was found that in the process of ion implantation, two types of new emission centers associated with Gd ions as well as Si quantum dots are formed in glassy silica. The distributions of excited states over the lifetime were found for both new centers and Si quantum dots. The nature of dispersion of the emission decay time was discussed in terms of structural disorder in the matrix. Thermal annealing and an increase in the ion fluence lead to the stimulation of the formation of Gd-related new centers and Si quantum dots. The micromechanisms for the formation of new Gd-related centers and two types of Si quantum dots were proposed on the basis of two scenarios for the introduction of Gd ions into the SiO 2 network: insertion of Gd into interstitial voids near oxygen-deficient centers and Gd  →  Si substitution with subsequent expulsion of Si atoms to the interstitial voids. New emission oxygen-deficient centers and quantum dots created by ion-beam technology in silica glasses are of interest for the development of new functional materials for photonics, and micro- and opto-electronics.

X-ray and optical spectroscopies were applied in order to study the band structure and electronic excitations of the SiO x /R y  O z (R  =  Si, Al, Zr) suboxide superlattices. The complementary x-ray emission and absorption measurements allow for the band gap values for the SiO x layers to be established, which are found to have almost no dependency on the cation type R. It is determined that, after annealing, the stoichiometric factor x remains near 1.8 in all the systems under study, implying that the silicon quantum dot synthesis reaction is not fully completed. It is shown that the SiO x /Al 2 O 3 multilayer contains octahedral structural motifs (SiO 6 ) usually found in stishovite, whereas SiO x /SiO 2 and SiO x /ZrO 2 demonstrate an electronic structure similar to conventional silica. The intrinsic electronic excited states are examined by means of synchrotron-excited photoluminescence spectroscopy. Low-energy UV-excited luminescence of SiO x layers is found to have the same spectrum in all of the studied structures, while VUV-excited spectra strongly depend on the cation R. In these measurements, manifestations of 'slow' exciton-mediated and 'fast' defect-related luminescence are distinguished using nanosecond time resolution. It is shown that both mobile and bounded excitons appear in the suboxide layer under 6.2 eV and 5.8 eV irradiation and then relax radiatively through the triplet-singlet transition of the neighbouring oxygen-deficient centers. The complete picture of the optical excitation and relaxation processes in these materials is illustrated in a general diagram depicting electronic states.

Optical and transport properties of nonstoichiometric tantalum oxide thin films grown by ion beam deposition were investigated in order to understand the dominant charge transport mechanisms and reveal the nature of traps. The TaO x films composition was analyzed by X-ray photoelectron spectroscopy and by quantum-chemistry simulation. From the optical absorption and photoluminescence measurements and density functional theory simulations, it was concluded that the 2.75 eV blue luminescence excited in a TaO x by 4.45 eV photons, originates from oxygen vacancies. These vacancies are also responsible for TaO x conductivity. The thermal trap energy of 0.85 eV determined from the transport experiments coincides with the half of the Stokes shift of the blue luminescence band. It is argued that the dominant charge transport mechanism in TaO x films is phonon-assisted tunneling between the traps.

The anomalous (τ < 10 ns) luminescence of wide bandgap crystals of lithium-gadolinium orthoborate Li(6)GdB(3)O(9) doped with trivalent cerium ions, has been revealed for the first time and investigated through the low-temperature time-resolved vacuum ultraviolet synchrotron spectroscopy. It was shown that the optical transitions at 6.2 eV are due to electron transfer from the ground 4f(1) states of Ce(3+) ion onto the autoionized states near the conduction band bottom of a crystal. These transitions lead to the formation of impurity-bound excitons in the form of correlated electron-hole pair, in which the hole component is localized at 4f-level of the cerium ion and an electron component is located at the conduction band bottom in the attractive potential of this hole. It is established that the direct radiative recombination of the cerium impurity-bound exciton leads to a fast broadband emission at 4.25 eV. The energy threshold for creation of the impurity-bound excitons was determined on the basis of the obtained spectroscopic data. We calculated the H(k) functions of distribution of the elementary relaxations over the reaction rate constants and explained on this basis the decay kinetics and quenching processes, not only for the anomalous emission at 4.25 eV, but for the ordinary 5d-4f luminescence at 3.0 eV in Ce(3+) ions. The paper discusses the decay channels for the impurity-bound excitons and their influence on the decay kinetics and spectra of luminescence in Li(6)GdB(3)O(9) crystals.

This research is focused on the 4f-5d transitions in Ce(3+) centers doped into tetragonal β-SrAlF(5) single crystals belonging to the I4(1)/a space group. The presence of four non-equivalent Sr(2+) sites in this compound leads to the appearance of three spectroscopically non-equivalent Ce(3+) luminescence centers, which can be well distinguished using a time-resolved laser spectroscopy technique. All 4f-5d transitions have slightly varying excitation and emission energies with characteristic probabilities resulting in several decay times that can be determined experimentally. One of these centers experiences strong perturbation due to a defect nearby, probably the O(2-) impurity ion substituting for the F(-) ion and acting as a charge compensator as well. Identification of these photoluminescence centers is performed using crystal field calculations. The crystal field parameters are calculated for two identified centers using the structural data for SrAlF(5); diagonalization of the crystal field Hamiltonian results in obtaining the splitting of the Ce(3+) 5d states. This method allows 'regular' unperturbed Ce(3+) centers with selected Sr(2+) sites to be assigned.

This paper presents the results of the study of electronic excitations in undoped LiBaAlF(6) single crystals by means of luminescence spectroscopy and complimentary optical methods. The intrinsic emission at 4.2 eV due to self-trapped excitons was identified. The fast nanosecond defect-related luminescence was revealed at 3.0 eV. Both emissions degrade under electron beam irradiation, the most probable reason of which is defect creation introducing an additional non-radiative relaxation channel prohibiting energy transfer to luminescence centers. These defects can be recovered and luminescence intensity restored at higher temperatures (>200 K). The permanent damage by electron beam irradiation results only in overall growth of the absorption coefficient in the whole 1.5-6.5 eV spectral region studied. The analysis of thermally stimulated luminescence glow curves in the temperature range of 5-410 K revealed two shallow charge carrier traps with the activation energies of 0.22 and 0.33 eV, respectively. The luminescence of an impurity peaked at 2.5 eV was found and tentatively assigned to an oxygen-related emission center.

Some regular features of the excitation energy transformation in anion-defective crystals of alpha-Al2O3 were analysed by the sub-nanosecond spectroscopic method. The samples were excited using synchrotron radiation and high-density pulsed electron beams. It was shown that much of the energy of the ionising radiation absorbed by the crystals was liberated as the luminescence of F- and F-centres immediately at the moment of irradiation. Luminescence of F+-centres dominated in the nanosecond range, while luminescence of F-centres prevailed in the millisecond range. The excitation energy transformation processes and their kinetics were governed by the temperature, the concentration ratio of intrinsic defects in alpha-Al2O3 crystals, and the excitation density.