Cheap vacuum-free method was used for doping ZnO films by silver.
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Hydrothermal annealing was applied to increase the luminescence intensity.
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Intensive violet band was obtained in the emission of ZnO films.
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Differences of violet radiation band from low-energy bands were revealed.
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Similarity was found in behavior of violet and ultraviolet bands.
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.
