The effect of hydrostatic pressure on the optical properties and electron energy levels in thallous halides

Abstract

Abstract Measurements have been made on the optical absorption of freely mounted thin crystals of TIBr, and evaporated films of T1C1, TIBr and TlI, from room temperature down to 4°K. The shift with pressure to 6 kbars of the sharp excitonic features has been followed at 80°K and 274°K. All the exciton peaks move to lower energies with pressure, but the spin-orbit doublet moves at a slower rate than the other peaks. The pressure coefficient of the energy of the first exciton peak (minimum gap) rises sharply with temperature above the Debye temperature (ca. 130°K). From these measurements information on the electron lattice interactions and deformation potentials has been obtained. A model for the band structure of TIBr and T1C1 has been outlined, based on an analysis of the optical spectra, pressure shifts and band structures of isoelectronic compounds. We thank Trinity College for the award of a studentship to A. J. G.; Gonville and Caius College for a Research Fellowship to W. Y. L.; and the Science Research Council for a grant to the laboratory.