Emission variety in ZnO nanocrystals obtained at different growth temperatures

Scanning electronic microscopy, X ray diffraction and photoluminescence have been applied to the study of structural and optical properties of ZnO nanocrystals prepared by the ultrasonic spray pyrolysis at different temperatures. The variation of temperatures and times at the growth of ZnO films permits modifying the ZnO phase from the amorphous to crystalline, to change the size of ZnO nanocrystals, as well as to vary their photoluminescence spectra. The study has revealed three types of PL bands in ZnO NCs: defect related emission in visible spectral range, the near-band-edge PL, related to the LO phonon replica of free exciton recombination, and IR emission that, apparently, is the second-order diffraction peaks of near band edge PL. The PL bands, related to the LO phonon replica of free exciton, in room temperature Pl spectrum testify on the high quality of ZnO films prepared by the ultrasonic spray pyrolysis technology.