Resonant two-photon absorption and emission in single-crystal thin films of CuCl

A comparative study of the luminescence and absorption spectra of excitonic molecules in thin films of cuprous chloride grown on sodium chloride and fused quartz is reported. Thin films of CuCl on NaCl are in single-crystalline form while CuCl on quartz are polycrystalline as evidenced by X-ray diffraction analysis. Under resonant excitation at 7 K, the two-photon absorption spectra for CuCl grown on NaCl exhibit a reduction in linewidth and an increase in the peak absorption as compared with those for CuCl grown on fused silica quartz. Also, the emission lines arising from the decay of excitonic molecules to exciton states are sharper in the single-crystal thin film. These results suggest that the recently grown CuCl single-crystal thin films are substantially superior to polycrystalline thin films for studies of picosecond biexcitonic optical bistability and Bose-condensation of excitonic molecules.