Spectroscopic manifestation of self‐trapping excitons in ionic insulators

Abstract

AbstractThe luminescence and excitation spectra of free and self‐trapped excitons, whose states are separated by a small potential barrier, are investigated experimentally on an example of NaI and RbI crystals. The height of the self‐trapping barrier is established to be independent of the kinetic energy of an exciton, but it is inversely proportional to its first quantum number. The spectroscopic manifestation of the self‐trapping barrier in the excitation spectra of the steady‐state luminescence of self‐trapped excitons is shown. The value of barrier height obtained experimentally coincides best of all with the value calculated from the theoretical model of the polarizing exciton. The evolution of the luminescence excitation spectra of self‐trapped excitons in a temperature interval 4.2 to 80 K is studied. If the relaxation mechanism of free excitons is reflected in the oscillating structure (the oscillation period is equal to the energy of LO phonon) of luminescence excitation spectra, then the further exciton relaxation along the adiabatic sheet is manifested most directly in the structure of hot luminescence spectra of the self‐trapping excitons.