Tuning of energy gap and photoluminescence behaviour of Zn0.96Ni0.04O nanostructure by Cr substitution

The Cr-doped Zn0.96Ni0.04O (Zn0.96-xNi0.04CrxO) nanoparticles with different Cr concentrations from 0 to 6 % have been synthesized successfully by sol-gel method. The obtained nanoparticles were systematically characterized by X-ray diffraction, energy dispersive X-ray spectra, scanning electron microscope, Fourier transformation infrared spectroscopy, UV-Vis spectroscopy and photoluminescence spectra. X-ray diffraction patterns revealed that Cr was incorporated into the ZnO crystal lattice without disturbing the original wurtzite crystal structure. The increase of lattice parameters by Cr-doping concluded that both Cr3+ and Cr2+ ions co-exist, and occupy Zn2+ in the ZnO host lattice. The observed higher transmittance, energy gap and emission intensity at Cr = 2 % indicate that this is selected as optimized Cr concentration in the host lattice. The blue shift of energy gap and the variation in intensity and position of emission bands in photoluminescence spectra were discussed based on size and defects density.