Environment-Friendly Synthesis of Undoped and Cu doped ZnO Nanoparticles and Study of their Optical Absorption Properties towards Biological Applications

Wet chemical method is a simple and cost-effective way to synthesize nanoparticles of high yield and mass production compared to other conventional methods. Besides, it does not require the maintenance of rigorous experimental conditions like high temperature, low pressure or flow of carrier gases. We have followed a simple wet chemical method to synthesize pure and Cu doped ZnO nanoparticles. Absorption spectroscopic study yields the absorption behavior of a material over a wide range of the electromagnetic spectrum. Absorption study of the synthesized undoped ZnO and Cu/ZnO reveals that doping with Cu decreases the absorption coefficient. It clearly indicates that the scattering of photons by phonons reduces due to Cu doping. The Urbach energy is an important parameter to understand the degree of disorder of phonon states in a material. It also enables us to study the dependence of the absorption coefficient on the wave-length of incident photons of energies lower than the band gap energy. For pure ZnO, the Urbach energy was calculated to be 0.511 eV and decreased to 0.483 eV upon doping with Cu in ZnO. The extinction coefficient was also calculated to understand the optical absorption process in the material.