Photoluminescence from heavy-hole and light-hole excitons split by thermalstrain in CuI thin films

We have investigated photoluminescence properties of heavy-hole and light-h ole excitons in 30-nm CuI thin films grown by vacuum deposition onto (0 0 0 1) Al-2 O-3, (0 0 1) NaCl, and (0 0 1) KCI substrates. In the absorption s pectra, the thermal-strain-induced splitting of the heavy-hole- and light-h ole-exciton energies is observed. The magnitude of the splitting energy dep ends on substrate materials. The free-exciton photoluminescence exhibits a remarkable dependence on the excitation energy. The peak energy and intensi ty of the photoluminescence oscillate with the period of the longitudinal o ptical (LO)-phonon energy reflecting intense nonequilibrium in the relaxati on process of the excitons. Furthermore, it is found that whether the excit on-splitting energy is smaller than the LO-phonon energy or not dominates t he final stage of the exciton-relaxation process. (C) 2000 Elsevier Science B.V. All rights reserved.