Highly Stabilized Monodispersed Citric Acid Capped $\hbox {ZnO:Cu}^{2+}$ Nanoparticles: Synthesis and Characterization for Their Applications in White Light Generation From U

Nanophosphors of ZnO:Cu²⁺ were synthesized by a chemical technique based on coprecipitation method. The synthesized nanophosphors were annealed at different temperatures (100-400°C) in steps of 100°C for 4 h. A reduction in photoluminescence intensity was observed with increase in the annealing temperature. Further, these nanophosphors were capped with citric acid, which results in enhancement in the luminescence intensity. These surface-modified ZnO nanoparticles were found to be remarkably stable. The reduction in luminescence with annealing temperature occurred due to removal of surface defects and intrinsic impurities, while the citric acid reduced the unsaturated bond density and passivated the surface, resulting in reduction in the number of surface trap sites for nonradiative recombination processes to occur, enhancing the luminescence intensity. Currently, LEDs giving UV emission have been combined with broadband visible green phosphors to make white-light LEDs. Thus, green luminescent ZnO:Cu²⁺ nanoparticles can be seen as necessary and critical constituent for white light generation from UV LEDs, underlying the findings and importance of current investigations. Besides this citric acid capped ZnO:Cu²⁺ nanophosphors can also be used in biological (drug delivery system, bioimaging, etc.) and biosensors.