OPTICAL PROPERTIES OF NANOSIZED ZINC OXIDE OBTAINED BY ELECTROCHEMICAL METHOD

For the synthesis of nanostructured ZnO, the electrolytic method developed by the authors was used, the advantages of which are the environmentally friendly and low-cost process, low synthesis temperatures (20-98°C), and no need for complex equipment. The developed method allows to obtain low-dispersion materials of different elemental composition, in particular, zinc compounds – ZnO and hydrozincite, which were studied in this work. Investigation of the samples by X-ray diffractometry (XRD) showed that the synthesized ZnO is characterized by the hexagonal structure of wurtzite, P63mc, and for hydrozincite – by the monoclinic prismatic structure C2/m. Studies of the synthesized nanocrystals (NC) of ZnO by scanning electron microscopy have shown that they form in the shape of rods and "nanostars", and their concentration increases with increasing electrolyte temperature during synthesis. At the same time, according to XRD, the concentration of hydrozincite in the synthesized powder decreases with increasing electrolyte temperature. It is established that the technological parameters of ZnO synthesis and subsequent annealing significantly affect the photoluminescence (PL) spectra. In particular, the effect of increasing the oxygen concentration in the electrolyte on the PL was investigated. It is shown that purging air through the electrolyte in the process of ZnO synthesis leads to a change in the number of photogenerating defects VO+ and Oi, which is manifested in a change in the intensities of individual PL bands. In particular, an increase in the intensity of ~ 440 nm PL band was registered, which is due to an increase in the number of defects associated with oxygen inclusions (Oi) in the ZnO lattice and the formation of hydrozincite (Zn5(OH)6(CO3)2); the formation of the latter was confirmed by X-ray diffraction. It has been shown that annealing of the powder synthesized with purging with air leads to an increase in the intensity of the exciton ZnO band, which is explained by thermal decomposition of hydrozincite to an "active" ZnO with a well-developed surface. It is demonstrated that the PL of the obtained phosphor based on ZnO NCs covers the entire visible spectrum, which is important for the creation of white light sources. In the resonant Raman spectra (lexcitation = 325 nm) of the annealed ZnO samples, only an A1(LO) first-order optical phonon is manifested at ~ 573 cm-1, and its overtones up to the 4th order, which confirms the high crystalline perfection of the synthesized ZnO material.