The violet luminescence band in ZnO and ZnO-Ag thin films

Abstract

The stationary and time-resolved photoluminescence (PL) spectra of ZnO films deposited on different substrates were studied. The intensive violet (V) emission centred at about 415–420 nm was observed at room temperature in photoluminescence (PL) spectra of the ZnO films. We found that the V-band is observed in all types of film, regardless of the type of substrate or the presence of a dopant. The ratio of intensities of violet and ultraviolet (UV) bands depends on temperature and duration of the heat treatment. It is also shown that the V band is not associated exclusively with the film surface states; instead, it is inherent in both the surface and the entire volume. The V band is of a complex shape and consists of 3 sub-bands with the maxima at 408, 414, and 421 nm. The relative contribution of each of the sub-bands is determined by the technological conditions of the film preparation. Analysis of obtained data allows us to conclude that the V-band is due to intrinsic defects of the ZnO film and can be attributed to the near band edge emission of ZnO.