Role of defects in optical, photoluminescence and magnetic properties of Zn0.96−xNi0.04CrxO nanoparticles

Abstract

Cr, Ni doubly doped ZnO nanoparticles for Cr = 0%–5% have been synthesized successfully by sol-gel route. X-ray diffraction spectra revealed the hexagonal wurtzite structure of the samples without any detectable secondary phases up to Cr = 3% and a secondary spine ZnCr2O4 phase was noticed at higher Cr doping (Cr = 5%). The rapid decrease in crystallite size derived from Debye formula by incorporation of Cr was understood in terms of the dissimilarity in ionic radii among Cr3+ (0.063 nm) and Zn2+ (0.074 nm). The shape of the synthesized nanoparticles and the generation of defect concentrations by Cr-doping in ithe host Zn-Ni-O lattice plays major role in the reduction of optical energy gap from Cr = 1% (Eg ≈ 4 eV) to Cr = 5% (Eg ≈ 3.87 eV). The broad and dominant infrared absorption peaks between 483 cm−1 and 490 cm−1 revealed the occurrence of Zn-O stretching mode with octahedral co-ordinates. The steady enhancement of green emission by Cr addition from photoluminescence spectra supports total increase of defect states like oxygen vacancies. Room temperature ferromagnetism was noted in whole Cr range where Cr = 3% scored maximum magnetization and dropped off for Cr = 5% due to the secondary ZnCr2O4 phase.