High pressure study of ZnSe:Cr2+ crystals: the origin of the 1.25 eV luminescence

High pressure studies of Cr2+ luminescence in ZnSe crystals were performed at low temperatures. In addition to the mid-infrared luminescence transitions from the first excited 5E level, higher energy luminescence was also observed. These two luminescence bands exhibit similar pressure coefficients but of opposite signs, which identify the origin of the higher energy band as the transitions from the second excited 3T1 level. At higher pressures, increased covalence effects are observed, which result in the appearance of an additional peak in the luminescence due to changes in the spin-orbit coupling strength.