OBSERVATION OF REDSHIFTS OF PHOTOLUMINESCENCE FROM THIN-FILMS ASSEMBLED BY CUCL NANOCLUSTERS

Two samples of thin films, assembled by CuCl nanoclusters, have been p repared by the gas evaporation technique. The CuCl nanoclusters were d eposited on monocrystalline silicon and quartz substrates and then coa ted with a layer of NaCl to prevent oxidation of the CuCl nanoclusters . From transmission electron microscope and selected area diffraction, it is clear that the two samples consist of CuCl nanocrystals and Cu aggregates and the mean diameters are about 3 nm and 6 nm. From the ab sorption and photoluminescence (PL) spectra of the two samples carried out at similar to 300 K, we found that the peaks of exciton absorptio n do not show up and luminescence peaks shift to lower energies, possi bly due to the strong coupling between exciton and phonon. At 77 It, t he PL peaks of excitons broadened by exciton-phonon coupling have been observed, in approximate agreement with the values calculated by the quantum confinement model. The broad peaks of emission from trapped st ates or bands have also been observed at 77 K. In addition, the intera ction between exciton and phonon is stronger in the sample with mean d iameter about 3 nm according to a larger broadening and redshift of th e PL peak from excitons, in qualitative agreement with theoretical pre diction.