About defect phenomena in ZnO nanocrystals.

ZnO nanocrystals are receiving renewed attraction due to their multifunctional properties. Selective enhancement and tuning of their optical and electrical properties are essential for achieving novel devices with accurate sensing and conducting capabilities. The nature and type of intrinsic defects that occur in ZnO influence these properties. In this work, we investigate the intrinsic defect structure of ZnO via electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy and correlate the results with existing computational works. Mainly, the defects are analysed by taking the microscopic defect structure of the lattice into account. The results manifest the core-shell model of the defect structure in ZnO. By default, specifically for nanocrystals, oxygen vacancies localise on the surface, while zinc vacancies localise in the core. The investigations in this report demonstrate that the concentration of the intrinsic defects and their position can be tuned merely by changing the size of the nanocrystal. Additionally, the UV, green, orange and red emissions can be tuned by nanocrystal's size and post-annealing treatments.