HYDROSTATIC-PRESSURE EFFECTS ON THE FREE AND SELF-TRAPPED EXCITON-STATES IN CSI

The s-like (Gamma(8)(-),Gamma(6)(+)) and d-like (Gamma(8)(-),Gamma(8)( +)) free exciton (FE) states and the corresponding self-trapped excito n (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 i s changed from the s-like (Gamma(8)(-),Gamma(6)(+)) state to the d-lik e (Gamma(8)(-),Gamma(8)(+)) state, and consequently the lowest-energy STE state is changed from the s-like state to the d-like state: The la tter 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 pres sure the s-like and d-like STE's fall into a quasithermal equilibrium distribution. Based on the results, we discuss the pressure-induced ch anges of the adiabatic potential energy surfaces of the STE states in CsI.