Pressure-dependent photoluminescence of ZnO nanosheets

Photoluminescence and Raman spectra of ZnO single-crystal nanosheets have been studied as a function of applied hydrostatic pressure using the diamond-anvil-cell technique at room temperature. The ZnO nanosheets synthesized via a vapor transport process have uniform plane surfaces with lateral dimensions up to several microns and thickness of similar to 100 nm. In terms of Raman results, the ZnO nanosheets underwent a transition from wurtzite to rock-salt structure with an increase of pressure, and the phase-transition pressure was measured to be about 11.2 GPa. However, a strong near-band-edge UV emission of ZnO nanosheets was observed with the applied pressure up to 20.0 GPa. Simultaneously, the emission peak shifted to higher-energy side with increasing pressure. By examining the dependence of the near-band-edge emission peak on the applied pressure, the pressure coefficient of the direct Gamma band gap in the wurtzite ZnO nanosheets was determined. (c) 2005 American Institute of Physics.