Effects of Hydrostatic and Chemical Pressures on Impurities Determined through Optical Parameters

Abstract

A survey on the influence of hydrostatic and chemical pressures upon optical properties due to Transition-Metal impurities in insulators is offered in this article. Aside from recalling the theoretical framework where the properties of impurities in insulating materials are reasonably explained particular attention is paid to the dependence of crystal field and charge transfer transitions upon the impurity-ligand distance, R . By means of 10 Dq dependent d-.d transitions or the energy of charge transfer transitions it is pointed out that j R variations around 0.1 pm can be detected. The R dependence of 10 Dq is shown to determine also the corresponding dependence of Huang-Rhys factors and Stokes shift. The Huang-Rhys factor, S A , of the A 1 local mode is found to increase when R does a conclusion supported by recent experimental data on Cs 2 NaScCl 6 : Cr 3+ under hydrostatic pressure. The increase of the Stokes shift when R increases observed in the series of cubic fluoroperovskites doped with Mn 2+ is also discussed. It is pointed out that for the same j R variation, j y A changes produced by chemical pressures can be bigger than those produced through a hydrostatic pressure.