Higher excited electronic states in clusters of ZnSe, CdSe, and ZnS: Spin-Orbit, vibronic and relaxation phenomena.

Metal selenide clusters have been made and characterized, using the arrested precipitation colloidal technique. A comparison of sulfide and selenide spectra enables observation of the effect of changes in the highest occupied molecular orbitals upon cluster electronic properties. The first and second excited electronic states are both observed as a function of size in ZnSe clusters. The systematic dependence of the spectra lead to assignment of the higher state to a 1S-type hole based upon the split-off valence band. It is shown that the energy spectrum of discrete hole states is controlled by the spin- orbit energy and the isotropic holes mass in small, highly symmetrical clusters. This result contrasts with the heavy hole and light hole states observed for planar confinement. ln ~-20angstroms diameter ZnS clusters, there is a strong vibronic temperature dependence in the excited state spectra, which we assign to Frohich coupling. We conjecture that lifetime broadening is severe in clusters of other, small gap materials.