SIZE-DEPENDENT HOMOGENEOUS BROADENING OF CONFINED EXCITONS IN CUCL MICROCRYSTALS

In nm-size CuCl microcrystals embedded in NaCl matrices, resonant luminescence spectra of the Z3 confined excitons were measured under size-selective excitation among the exciton absorption band, inhomogeneously broadened due to the size-distribution of the microcrystals. The temperature- and size-dependences of the homogeneous line width of the confined exciton absorption with the lowest energy could be derived from the bandwidth of the exciton resonant luminescence. Based on the analysis similar to that for the line width of the free excitons in a bulk crystal, it is found that with decreasing microcrystal size the short-range deformation-type interaction of confined excitons with LA phonon becomes more and more important for the broadening, mainly because of the localization of the vibrational motion, while the Frohlich-type interaction with LO phonons does not change much on account of its long-range interaction.