ИСТИНА

Mixed crystals in the form of substitutional solid solutions are promising scintillation materials for applications in high-energy physics, nuclear medicine, etc. Indeed, in recent years it has been demonstrated that solid solutions of scintillation materials in a large number of cases have a higher quantum yield, better energy resolution and faster luminescence with less afterglow compared to pure substances. This behavior is associated with a significant change in the dynamics of electronic excitations at the thermalization stage, when hot charge carriers start to lose their energy, undergoing inelastic scattering by phonons. The kinetic energy of charge carriers at this stage of relaxation does not exceed the band gap and occurs to be about several eV for typical scintillators. At these energies, the conduction band and the valence band of a dielectric crystal have a complex structure, characterized by the presence of a large number of branches of the dispersion law. In this regard, estimations of the efficiency of scattering of electronic excitations by phonons, made in the simplified approximation of one parabolic branch of the dispersion law, seem to be far from reality. In addition, in solid solutions with substitutional disorder, this scattering mechanism is supplemented by scattering of charge carriers by spatial fluctuations of potential. However, the efficiency of this scattering in the Born approximation in the model of a single parabolic branch band turns out to be insufficient to explain the reduction in the thermalization length and an increase in the efficiency of carrier recombination in solid solutions of scintillation crystals. In this work, the elastic (on potential fluctuations) and inelastic (on phonons) scattering of hot charge carriers in the approximation of multiple parabolic branches of the dispersion law are considered. The processes of migration and recombination of charge carriers in this approximation and their influence on the observed optical properties of substitutional solid solutions are investigated. It is shown that presence of several branches of the dispersion law in the conduction band of dielectric crystal accelerates the relaxation of electronic excitations and leads to a decrease in the thermalization length, thus resulting in the increase of the recombination efficiency.