On the thermal ionization of dielectron centres in ionic crystals

The energy required for the thermal ionization of pairs of electrons trapped in ionic crystals by point defects of positive charge ze (z≥2) has been evaluated. Utilizing a simple trial function of the form ψ(πa3)-1/2exp(-r/a) to represent the electron ground state in dielectron centres, it is shown that Lehovec's previous results (Lehovech, Phys. Rev., 92 (1953) 253) are reproduced with an effective extra-charge (z-5/16) e. The parameter a is determined by variational calculus. Results are compared with experimental data on thermal ionization energy in ZnS and CdS