Tuning of ultra-violet to green emission by choosing suitable excitation wavelength in ZnO: Quantum dot, nanocrystals and bulk

ZnO particles (quantum dots to bulk) have been prepared using urea hydrolysis and are dispersible in methanol. In photoluminescence study, as-prepared sample shows the main emission peaks at 375 and 394 nm, which are assigned to the exciton and band-edge emissions, respectively. The former peak disappears when as-prepared sample is heated at 300, 500, 700 and 900 °C due to particle size effect. Interestingly, higher heated samples shows emission peak at 505 nm and it is attributed to oxygen vacancy created in ZnO lattice. The intensity ratio of UV-light at 394 nm to green light at 505 nm can be adjusted by choosing suitable excitation wavelengths and also particle size or heat-treatment. Optimum emission intensities at 394 and 505 nm can be obtained on 360–370 and 320–330 nm excitations, respectively. These materials will be useful in optoelectronic applications.