Band structure of alkali metal sulfates

Abstract

The spectra of the creation of the main emission bands at 3.65 ÷ 4.0 eV and the long-wavelength emission bands at 3.0 ÷ 3.1 eV, 2.6 ÷ 2.7 eV, and 2.3 ÷ 2.4 eV in K2SO4 crystals and Na2SO4 at temperatures of 15-300 K was investigated. It is shown that these emissions are excited by low-energy photons with an energy of 4.6 ÷ 6.2 eV, as well as high-energy photons of 6.4 ÷ 10.5 eV. During excitation, electrons from 1t1 , 3t2 ,e, 2t2 orbitals of the valence band transfer to the state of the cation in the conduction band. Holes arising in these orbitals, float to a level above the valence band and are localized. The main emission of 3.65 ÷ 4.0 eV arises when electrons recombine with these localized holes located above the valence band.