Study on bound exciton dynamics in CdS crystals at acoustic driving

Abstract

A variety of ps transient and cw optical techniques including photoluminescence (PL), Raman scattering and optical absorption spectroscopy has been applied to elucidate acoustically driven bound exciton dynamics. The lifetime of the I 1 bound excitons in CdS platelets is found to be initially enhanced with increasing driving amplitude whereas a drop in the lifetime is achieved at sufficiently high drivings. The line shape of the I 1 exciton PL lines experiences remarkable broadening in the region of the lifetime decrease and this is accompanied by a reduced light emission in the acoustic phonon wing of the I 1 exciton PL line. Additionally, an enhancement of the E 1 LO phonon resonant Raman line and an appearance of the A 1 LO phonon Raman line, normally forbidden in the employed scattering geometry, are achieved by increasing the driving amplitude. The detailed analysis of the observations is made within the framework of internal electric fields generated by the driving. It is shown that the effects presented can be reasonably well understood by taking into account both the long-range electric fields and nonuniform microfields accompanying acoustic driving. It is shown that the microfields likely arise from variations in the local-crystal environment at the exciton site imposed by the driving.