Optical, structural and radiospectroscopic studies of ZnO/MnO nanostructures synthesized by ultrasonic spray pyrolysis

The technology for the synthesis of nanocrystals (NCs) of pure ZnO and ZnO doped with a magnetic Mn impurity in concentrations of 2% and 4% by ultrasonic spray pyrolysis has been developed. The structural, morphological and optical properties of syntesied ZnO NCs have been studied with methods of X-ray diffraction, scanning electron microscopy, electron paramagnetic resonance (EPR), spectroscopy of Raman scattering and photoluminescence. The defective near-surface layer in ZnO:Mn NCs has been identified based on the analysis of the EPR spectra. Thermal annealing of samples at T = 850°C leads to the ordering of the crystal structure of ZnO:Mn NCs. The solubility limit of the Mn impurity is less than 2%. Raman spectra analysis has revealed that ZnO:Mn NCs are covered with ZnMn2O4 and d--MnO2 shells. A significant increase in the intensity of exciton photoluminescence for ZnO NCs caused by the improvement of the structural perfection of NCs is to be a result of increasing the liquid flow rate to 40 l/h during the synthesis process. Thus, the optimal technological regimes to form high-quality, structurally perfect ZnO NCs can be elaborated by changing the liquid flow rate during the synthesis process.