  We present the results of experiments on synthesis of ZnO nanoclusters by
reactive pulsed laser deposition (PLD). The nanoclusters were formed and
crystallized in the gas phase and deposited on SiO2 substrates. The
nanostructured films were characterized by conventional photoluminescence (PL).
The PL spectra consist of a narrow UV excitonic band and a broad visible band
related to defects in the film. The film preparation conditions such as the
substrate temperature, ambient gas nature and pressure, were optimized in order
to increase the intensity of excitonic emission and prevent the formation of
defects. A post-growth annealing by UV laser radiation improved the optical
quality of the deposited films. The photoluminescence intensity was found to be
dependent significantly on the laser fluence and on the number of shots per
site. The nature of the defects responsible for the observed luminescence in a
visible range is discussed.
