Luminescence of excitons in mesoscopic ZnO particles

Luminescence and time-resolved luminescence spectra of ZnO particles with the size of ∼20 nm have been investigated under band-to-band excitation. In the ultraviolet spectral region, there appear broad luminescence bands at 367.6, 368.8, 374.5 and 381.9 nm at 10 K. Decay profiles at 369 and 374 nm exhibit two decay components. The decay times are ∼20 and ∼100 ps for 369 nm, and ∼40 and ∼400 ps for 374 nm. These luminescence bands are attributable to the radiative recombination of free and bound excitons. Based on the present results, the effects of surface states and defects on excitons in mesoscopic ZnO particles have been discussed.