Exciton luminescence spectra of CuCl films and their change by photo-irradiation

We have observed luminescence spectra of vapor-deposited CuCl films on rutile image under photo-irradiation with picosecond light pulses at 4.6 K. Decrease in the image-exciton and image luminescence intensities and an appearance of new exciton luminescence are found to be induced by the photo-irradiation. From the excitation photon energy dependence of the luminescence spectra, it is found that the image-exciton luminescence is resolved into two components: one is attributed to the optical phonon Raman lines and the other to the free image-exciton luminescence. The intensity of the Raman lines resonantly increases at the image-exciton band resulting in the optical phonon structures in the excitation spectrum. The excitation spectra of the new exciton and image luminescence are similar to the absorption spectrum of CuCl, which suggest that the resonant Raman process observed in the image-exciton luminescence hardly contributes to the generation of the excitons associated with the new exciton and image luminescence.