Hydrostatic pressure effects on the free and self-trapped exciton states in CsI.

Abstract

The s-like (${\mathrm{\ensuremath{\Gamma}}}_{8}^{\mathrm{\ensuremath{-}}}$,${\mathrm{\ensuremath{\Gamma}}}_{6}^{+}$) and d-like (${\mathrm{\ensuremath{\Gamma}}}_{8}^{\mathrm{\ensuremath{-}}}$, ${\mathrm{\ensuremath{\Gamma}}}_{8}^{+}$) free exciton (FE) states and the corresponding self-trapped exciton (STE) states in CsI have been studied under hydrostatic pressure up to 1.3 GPa. As the pressure is increased, the lowest-energy FE state is changed from the s-like (${\mathrm{\ensuremath{\Gamma}}}_{8}^{\mathrm{\ensuremath{-}}}$ ,${\mathrm{\ensuremath{\Gamma}}}_{6}^{+}$) state to the d-like (${\mathrm{\ensuremath{\Gamma}}}_{8}^{\mathrm{\ensuremath{-}}}$,${\mathrm{\ensuremath{\Gamma}}}_{8}^{+}$) state, and consequently the lowest-energy STE state is changed from the s-like state to the d-like state: The latter is evidenced by the replacement of the s-like STE luminescence (3.7-eV band) by the d-like STE luminescence (4.7-eV band). At high pressure the s-like and d-like STE's fall into a quasithermal equilibrium distribution. Based on the results, we discuss the pressure-induced changes of the adiabatic potential energy surfaces of the STE states in CsI. \textcopyright{} 1996 The American Physical Society.