The influence of the pressure and temperature on the light emission of the ZnO

A new route for the preparation of zinc oxide powder is described along with its characterization. A proteic sol was prepared dissolving zinc nitrate in filtered coconut water. After calcination at 1000 degrees C. the powder was compressed to 1.3 x 10(8) Pa and ZnO pellets were obtained. The emission spectra were recorded under UV excitation at 325 and 400 nm. The powder showed no spectroscopic response, whereas one peak around 396 nin was observed for the pressed powder (pellet with no heat treatment). The pellets were then annealed for 24h at 500, 800 and 1000 degrees C. In the first case, bands at 396 and 440nm and a structure of narrow peaks around 480nm (oxygen vacancies) were observed. Increasing the annealing temperature led to a decrease in the intensity of the emissions at 440 and 480 nm. We propose that the high pressure induces a red-shift in the UV region of the ZnO nanopowder emission peaks to 396 nm. This is an indication that the ZnO nanopowder treated under pressure and sintering temperature exhibits the spectroscopic behavior characteristic of the ZnO single crystal. The disappearance of the 440 and 480 nm lines indicate the reduction of oxygen vacancies. The atomic force micrographs suggest a coalescence thermal point. (C) 2007 Elsevier B.V. All rights reserved.