Abstract
Abstract In the present study ZnO nanocrystals embedded in a SiO 2 matrix were successfully produced by means of radio frequency magnetron sputtering deposition using ZnO and SiO 2 targets. Multilayer structures consisting of ZnO/SiO 2 bilayers were deposited on Si substrate wafers either in vacuum or in an oxygen-rich ambience. Subsequently, the structures were heat-treated at different temperatures and in different atmospheres. This procedure resulted in spherical ZnO nanocrystals with a narrow size distribution as determined by transmission electron microscopy. Photoluminescence (PL) properties of the ZnO nanocrystals were studied by means of steady-state luminescence spectroscopy with excitation in the blue-UV spectral range. The PL properties of the samples were observed to depend strongly on the ZnO nanocrystal size. A broad PL band in the visible spectral range is observed and is tentatively ascribed to defects on or in the vicinity of the nanocrystal surfaces. Sharp characteristic PL lines in the UV range were detected in relatively large ZnO nanocrystals. These lines are tentatively attributed to bound exciton and donor–acceptor pair recombinations, and they are similar to the corresponding lines observed in bulk ZnO. The role of surface defects for the PL properties of nanocrystalline ZnO is discussed.
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