Photoluminescence engineering in polycrystalline ZnO and ZnO-based compounds

The results of the investigations of photoluminescence (PL) in ZnO and ZnO-based composite materials are presented. The PL and PL excitation (PLE) spectra of undoped and doped with I group elements or rear earth ions ZnO polycrystalline films, ZnO, Zn_1–xMg_xO and ZnMgO–TiO₂ ceramics were studied. The structural properties of the samples were investigated with X-ray diffraction. Polycrystalline films were prepared by a screen-printing method and annealed at T_S= 500–1000 °C. The films annealed at T_S< 800 °C exhibited intense UV emission, whereas defect-related one appeared at 800 °C and enhanced with increasing T_S. Improvement of the PL and structural characteristics of ZnO films due to Li-doping were achieved. The PL bands caused by Sm and Ho ions were observed under ZnO band-to-band excitation. In the PL spectra of ZnO and Zn_1–xMg_xO ceramics, two types of PL bands were separated: i) the bands, whose spectral positions were not influenced by the Mg content (green Cu-related as well as self-activated orange and red ones); ii) the bands, spectral positions of which exhibited some blueshift with increasing Mg content (orange Li- and Ag-related and self-activated green ones). In the PL spectra of ZnMgO–TiO₂ composites, an intense red emission was found to appear in addition to the broad blue-orange band inherent in ZnMgO alloy. The red emission was ascribed to Mg₂TiO₄inclusions in ZnMgO matrix