[Spectral analysis of ZnO nanocrystals]

ZnO nanocrystals with different size were prepared with deposition method at different annealing temperatures. The images of transmission electron microscopy show that the nanocrystals have a good dispersion characteristic, uniform shape, and centralized distribution. The X-ray diffraction spectra of samples show that the size and the crystallization of the nanocrystals increase as the annealing temperature grows. The peak positions of ultraviolet and visible spectra exhibit a blueshift as the crystal size decreases, which demonstrates the quantum confinement effect of ZnO nanocrystals. The infrared spectra present that there are a few residual ions adhering to the surface of ZnO nanocrystals. In addition, it was observed in the infrared spectra that the peaks at about 430 cm(-1) shift to the red and become broader with the decrease in particle size. Two emission bands were clearly observed from the photoluminescence spectra of the samples. One is a relatively narrow emission band in the ultraviolet region (360 nm), while the other is a broad emission band in the visible region (468 nm). Compared with the theoretical calculation it is suggested that the latter originates from the zinc vacancies.