The decay of infrared luminescence in II-VI compound semiconductors doped by 3d transition elements

Abstract

The decay processes of infrared emission after laser excitation have been studied in a sampling technique for several crystalline II-VI materials: ZnS and/or CdS doped by V, Cr, Co, Ni or Cu. From the exponential decay curves with time constants 0.5<or= tau <or=50 mu s recorded at low temperatures, transition probabilities have been derived and compared with calculated electric-dipole matrix elements. Two different interactions are considered by which the parity-forbidden d-d transitions of 3d impurity ions become allowed: in a covalent model, the contribution of the wavefunctions of neighbouring ions is treated by LCAO-MO methods. In a configuration mixing model, lattice vibrations induce a mixing of 4p states of the transition-metal ion with the 3d levels. Configuration mixing appears to be the prevailing mechanism for the internal transitions considered here. The temperature dependence of the lifetime from 4 to 300K is also studied and can be interpreted by means of a configuration-coordinate model.