Defect induced band gap narrowing of zinc oxide nanoparticles using li + , na + and k + metal ions as a dopant

Abstract

ZnO nanoparticles have been synthesized by precipitation method from zinc acetate dihydrate and sodium hydroxide. The obtained precipitated compound was calcined at 4000 C for 2 hr and then, the obtained product was dissolved in deionized water. The prepared solution was characterized by UV-visible spectrophotometer and it was show absorption maxima at 380 nm and particle size of 3.6 nm that was almost equal to 4 nm, not exhibiting band gap enlargement. The band gap energy was lower for synthesized ZnO nanoparticles (3.263eV) than their bulk counterparts (3.37 eV), indicating high conductivity than the bulk ZnO powder. Zn1-xLixO, Zn1- xNaxO and Zn1-xKxO (where x= 0.005, 0.01, 0.015 and 0.02 M for all dopants) doped ZnO nanoparticles was prepared and calcined at 4000C for 2 hr and their solution was then characterized by UV-vis spectrophotometer. All concentration of Li+ doped ZnO nanoparticles was more narrowing the band gap of the undoped ZnO nanoparticles than Na+ and K+ doped ZnO nanoparticles. Both the size and concentration of dopants were affecting the band gap energy of ZnO nanoparticles. As the concentration and ionic radii of the dopants increases the optical band gap energy was also increasing. So the highest band gap energy was obtained by 0.015 and 0.02 M K+doped ZnO nanoparticles. The band gap narrowing was necessary to absorb photons with a wide range of energies, so Li+ doped ZnO nanoparticles was used to absorb photons in the portion of the solar irradiance with a high intensity than other dopants (Na+ and K+).