The temperature variation of the luminescence of the A-center (a Cd-vacancy plus halogen-donor pair) was calculated by assuming a temperature-dependent electron-ion interaction. The photoluminescence lines of the A-center underwent a pronounced shift at temperatures of between 4 and 50K. The zero-phonon line was explained in terms of a donor-acceptor pair transition, and the temperature dependence was not thought to be due to thermal expansion of the crystal. It was concluded that it resulted from excitations of electrons from the shallow levels of isolated halogen donors and from transitions from the conduction-band edge into the deep acceptor level of the A center.

S.Biernacki, U.Scherz, B.K.Meyer: Physical Review B, 1993, 48[16], 11726-31