The project is aimed to solve a fundamental problem connected with the study of regularities and mechanisms of charge transfer processes and their role in the formation of luminescent properties of low-dimensional nonstoichiometric binary and multicomponent oxides. The study of charge transfer processes in wide-gap dielectrics is an actual problem in condensed matter physics, since these processes determine many of the radiation-optical, luminescent, and electrical properties of materials. Of special interest is the study of such processes in the presence of cluster defects and impurity centers in the material capable of capturing free charge carriers. The established regularities of relaxation processes in clusters with defects, well-founded models and mechanisms will allow developing physical principles for controlling the properties of luminescent sensors for measuring the parameters of radiation and temperature fields in solving problems of ensuring radiation safety of the population and combating terrorism.
Low-dimensional phosphors with high luminescence intensity can be created on the basis of wide-gap metal oxides during sintering under reducing conditions. These conditions stimulate the formation of oxygen nonstoichiometry and cluster defects in the material. To obtain high luminescence intensity of investigated samples the technique of thermochemical coloration will be used with high temperature treatment (up to 1700оС) of nanopowders in a vacuum in the presence of carbon in form of graphite to create strongly reducing conditions. This method allows to obtain in heat-treated oxides a high concentration oxygen vacancies, as well as to introduce impurity atoms into defects created during high-temperature synthesis in the lattice site of the initial oxide. A wide class of anion-defective oxides of aluminum, magnesium, zirconium, nickel, cadmium, yttrium and manganese марганца (Al2O3, MgO, ZrO2, NiO, CdO, Y2O3, MnO2), as well as complex multicomponent materials based on them, including the above oxides doped with impurities of chromium, manganese, magnesium, lanthanum, cadmium, sodium, nickel and zinc (Cr, Mn, Mg, La, Cd, Na, Ni и Zn), mainly in the form of ultrafine ceramics synthesized from nanopowders, will be used as objects of research in the claimed project.
To create non-stoichiometry and cluster defects in wide-gap oxides, along with the thermochemical, radiation coloration of the samples will be used. Comparative analysis of luminescent properties of radiation- and thermochemically colored oxides using the methods of photoluminescence (PL), pulsed cathodoluminescence (PCL), thermostimulated luminescence (TSL), photostimulated luminescence (PSL) with the using of EPR spectroscopy will allow to establish general regularities of influence of nonstoichiometry on the processes of charge transfer with the involvement of clusters of traps. High-dose (more than 1 kGy) pulsed electron beam irradiation with an electron energy of 130 keV for luminescence excitation in oxides is planned in this study. It should be noted that the value of the electron energy (130 Kev) is significantly lower than defects formation energy in the materials under study. Therefore, the applied electron irradiation does not directly lead to the formation of oxygen vacancies in the investigated oxides, but only stimulates the formation of aggregate clusters of defects and changes the charge state of traps and recombination centers.
Original computational algorithms and software based on the Monte Carlo method were developed for modeling the processes of charge transfer in cluster systems. The necessity for this approach derives from the fact that the standard methods for calculating the kinetics of luminescence based on the numerical solution of differential kinetic equation system are not applicable in cluster in contrast to the system with uniformly distributed defects. Carrying out such calculations would allow to justify theoretically the experimentally observed regularities of luminescence as well as to predict new effects, related to processes of charge transfer in cluster systems.
The new scientific idea underlying this work is the determination of the fundamental mechanisms and features of the relationship between the luminescent properties of ultrafine ceramics based on wide-gap oxides and their structural features arising from the presence of clusters of intrinsic and impurity defects.
The novelty of the research:
1. The parameters of multistage synthesis of the wide-gap oxide ceramics affecting their luminescent properties will be determined experimentally, and the role of these parameters in the formation of the luminescence quantum yield will be quantified.
2. For the first time the luminescence mechanisms of the studied materials synthesized in different conditions will be identified, as well as the nature of defect clusters formed in the samples as a result of doping with impurities and thermochemical and radiation coloration will be determined.
3. For the first time general regularities and features of luminescent properties of a wide class of oxide dielectrics doped with various metal impurities will be formulated on the basis of experimental data analysis from PCL, TL, PL, PTTL and PTSL.
4. For the first time new regularities will be experimentally established and kinetic models of charge transfer processes in low-dimensional anion-defective oxides containing defect clusters will be developed.
The results of research into the influence of the material structure, including impurity centers and non-stoichiometry in oxygen, on luminescent properties obtained within the framework of this scientific work will deepen the existing fundamental ideas about the role of the structural state in the formation of the properties of oxide dielectrics. In the case of the development of a procedure for the synthesis of oxide systems with cluster defects and impurity centers sensitive to high doses of ionizing radiation, it is possible to use them as experimental samples of dosimetric detectors. Based on the data of the experimental study, it will be possible to create effective luminescent materials possessing a high luminescence intensity for future use in optoelectronic and nanoelectronic devices