"White" emission of ZnO nanosheets with thermal annealing

Photoluminescence (PL), its temperature dependence, scanning electronic microscopy (SEM) and X ray diffraction (XRD) have been studied in thermal annealed crystalline ZnO nanosheets. ZnO nanosheets were created by the electrochemical (anodization) method using different technological regimes with the typical size of 50 nm x 100 nm. Then ZnO nanosheets were annealed at 400°C for 2 h in ambient air. XRD study has shown that thermal annealing stimulated the Zn oxidation and ZnO crystallization with the creation of wurzite ZnO crystal lattice. The oxidation and crystallization processes in ZnO nanosheets are accompanied by the intensity increasing a set of PL bands with the peaks at 1.58, 1.98, 2.55, 2.94, 3.06 and 3.18 eV at 10 K. The reasons of emission transformation and the nature of optical transitions related to the studied PL bands have been discussed. It is shown that by the controllable way it is possible to obtain the wide spectral range for ZnO emission that is interesting for the room temperature "white" light-emitting diodes.