Investigation of energy band gap and its correlation with vacancy defects in Pb1-xNixO nanoparticles synthesized through sol-gel method

Nickel doped lead oxide (Pb1-xNixO) nanoparticles with different concentration (x = 0.00, 0.01, 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30) of nickel ion were prepared through a sol-gel route of synthesis. X-ray diffraction and transmission electron microscopic techniques confirmed the nanocrystallinity of the samples as the average sizes of the crystallites were found within 9-25 nm. The substitution of Pb2 + with Ni2 + caused of decrease of particle size with the increase of Ni2 + concentration. The EDS analysis confirmed the present of nickel ion in the Ni doped PbO nanocrystallites. The FT-IR spectra of the samples recorded to look for the distinct absorbance bands highlighting the atomic vibrations. The optical band gap energies (E-g) increased when the nanocrystallites became smaller in size. There is possibility of increase in vacancy defect concentration due to Ni doping that may also be the cause of E-g enhancement. The latter aspect is attributable to the onset of quantum confinement effects as seen in the case of a few other metal oxide nanoparticles. Positron annihilation studies focused on the vacancy type defects which were present in abundance in the samples and played crucial roles in modulating their properties. The concentrations of defects were significantly larger in the samples of lower crystallite sizes. The results supported the feasibility of tailoring the properties of lead oxide nanocrystallites for technological applications apart from the physical insight into the structural build-up when crystallites were formed with finite number of atoms and their distribution governed by site stabilization energy considerations. [GRAPHICS] .