The dissertation is devoted to solving an important scientific problem related to clarifying the photo- and thermally stimulated electronic processes features, in particular, establishing the mechanisms of luminescence and excitation energy transfer, studying the nature of trap levels and recombination centers of charge carriers in gallium and aluminum oxides doped with transition (Cr3+, Mn2+) and rare-earth (Tb3+, Eu3+, Yb3+) metals.
The spectroscopic characteristics of Cr3+ ions in -Ga2O3: 0.05 % Cr3+ single crystals were studied in detail in a wide temperature range of 4.5300 K. It was demonstrated that-Ga2O3: Cr3+ single crystals is the perspective material for non-contact temperature monitoring within the range 30-250 K. It was shown that the position of the maxima of thermally stimulated conductivity in -Ga2O3 crystals in the temperature range 85–400 K correlates well with the position of TSL maxima of undoped gallium oxide crystals, which indicates the electronic nature of charge carrier trap centers. A model of local energy levels in -Ga2O3 single crystals, which explains the observed dependences of impurity luminescence yield, mechanisms of TSL and photoconductivity occurrence was proposed.
It was established that the emission of Cr3+ ions is presented in all TSL maxima of Gd3Ga5O12: Cr polycrystals and the spectral composition of the thermostimulated luminescence coincides with the PL spectrum recorded at the corresponding temperature. This indicates that the radiative recombination under the condition of the release of carriers from the trap centers occurs through the same centers of Cr3+ as in the modes of PL and stationary radioluminescence. It was demonstrated that the effect of annealing in oxidizing or reducing atmospheres on the luminescence intensity of Gd3Ga5O12: Cr, Mg single-crystalline films is associated with a change in the ratio of Cr3+ and Cr4+ ions in the octahedral positions of the garnet structure. The luminescent characteristics of Bi3+ ions, which are included in the single-crystalline films Gd3Ga5O12, Gd3Ga5O12: Cr and Gd3Ga5O12: Cr, Mg as components of the flux under the film growth, are analyzed.
It is established that the relative intensity of Tb3+ emission in the green spectral region (5D4→7Fj transitions) prevails over the emission in the violet-blue region (5D3→7Fj transitions) for the concentration of Tb3+ activator 1 mol.% in micro- and nanoceramics of Gd3Ga5O12: Tb3+.The luminescence efficiency in the green spectral region in Gd3Ga5O12: 1 mol.% Tb3+ nanoceramics increases approximately threefold comparison with the intensity of activator luminescence in polycrystals, which is important when used such nanoceramics as phosphors of green luminescence. Mechanisms for IR photoluminescence quenching in Y3Al5O12: Yb3+ epitaxial films and nanopowders are proposed. The influence of annealing in the air on the kinetic characteristics of Yb3+ ions was studied and the IR photoluminescence quenching concentrations in Y3Al5O12: Yb3+ nanopowders were calculated.
It was revealed that the coordination polyhedron around Eu3+ ions is rather distorted or asymmetric, ie Eu3+ ions occupy positions with low local symmetry without the center of inversion in the spinel lattice of MgGa2O4: Eu3+, Mn2+ and ZnGa2O4: Eu3+, Mn2+ polycrystals. An orange glow with dominant 5D0→7F1 electric dipole transitions in Eu3+ ions at 593 nm was detected in Lu3(Ga, In)5O12: Eu3+ epitaxial films under the UV excitation. It indicates high symmetry of the local environment of Eu3+ ions in such films. It has been shown that magnesium and zinc gallates doped with Eu3+ and Mn2+ ions can be used as phosphors in LEDs because they allow controlling the color of the emission by changing the excitation wavelength and/or the concentration of the activator.
It is shown that deep traps in MgGa2O4:Mn2+ and ZnGa2O4:Mn2+are stable and can be used in dosimetry. At the same time, shallow traps are responsible for the long afterglow of gallates. Considerable attention is paid to the study of the phenomenon of optically stimulated luminescence (OSL) in magnesium and zinc gallates, as well as yttrium orthoaluminate (YAlO3), activated by Mn2+ ions. The irradiation dose readout can be realized by optical stimulation in continuous-wave or pulse-modulated modes. Dose dependence of the integrated signal of time-resolved OSL of the YAlO3: Mn2+ single crystals demonstrates that the dose-response remains linear at radiation doses up to almost 1 kGy, which is important for practical application of yttrium orthoaluminate doped with Mn2+ ions in the dosimetry of ionizing radiation.
The results obtained in this dissertation can be used for the predicted modification of luminescent and electrical properties of oxide materials of functional electronics based on gallium and aluminum by changing the defective structure, type, and concentration of impurities, which is important for practical application.
