Trend in the local-force variations due to substitutional transition-metal impurities in ZnS

Abstract

Numerical calculations of the impurity-induced Raman scattering intensity in ZnS crystals are made on the basis of Green's function theory. The isoelectronic defects studied consist in a series of substitutional transition-metal impurities (Cr, Mn, Fe, Co, Ni) with a variable number of 3 d electrons. The calculated results provide very good correspondence with all the existing experimental data, by considering that the impurity-sulfur bonds weaken by about 10 %. A monotonic evolution of the local force variations is found when going through the series of impurities : from Chromium to Nickel, the weakening of the bonds is decreasing. This trend appears to be a specific property of the transition-metal impurities, and a tentative explanation for it is proposed.