THE PRESSURE-DEPENDENCE OF THE INTRAIMPURITY ABSORPTION AND THE CHARGE-TRANSFER PROCESS OF ZNS-NI AND ZNSE-NI

The absorption spectra of ZnS:Ni and ZnSe:Ni were measured at 100 K under hydrostatic pressure up to 10 GPa. Two kinds of optical transition were investigated: (i) the d-d transitions between crystal field levels of Ni2+ in the tetrahedral held of the host lattice and (ii) a charge transfer band that occurs when an electron is transferred from the valence band to the Ni2+ ion. The pressure dependence of the crystal field parameter Dq and of the Racah parameter B were determined and a revised assignment of the d-d transitions was obtained. The charge transfer can be considered as a deep-acceptor transition. In this case the Ni acceptor level may be used as an energy reference, which enabled us to determine the hydrostatic deformation potential of the valence band.