We have prepared zinc oxide nanocrystals using a new type of solid-state reaction. The nanosized grains were obtained by changing the heat treatment temperature and the sizes were determined to be from 10 to 42nm.The lattice vibrational Raman spectra were measured and assigned at different grain sizes. We observed a strong visible emission centred at 580nm in the nanosized ZnO at room temperature. We have investigated the photoluminescence properties under different grain sizes after annealing. The weakening of the luminescence is attributed to the decrease of intrinsic structural defects, mainly, oxygen vacancies and the increase of the grain size in the nanocrystals.