Optical properties of Cr doped ZnAl2O4 nanoparticles with Spinel structure synthesized by hydrothermal method

Zn1-xCrxAl2O4 (x = 0, 0.01, 0.03, 0.05 and 0.07) nanoparticles were synthesized by hydrothermal method and heat treatment technology, and the effects of Chromium doping ratios on the microstructure, morphology, element distribution, binding energy and optical property of the samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), x-ray energy dispersive spectroscopy (XEDS), x-ray photoemission spectroscopy (XPS), ultraviolet-visible (UV-vis) spectroscopy, photoluminescence spectra (PL) and fourier transform infrared spectroscopy (FT-IR). The experimental results show that Zn1-xCrxAl2O4 nanoparticles possess cubic spinel structure without other impurity phases. The average crystallite size decrease and the lattice parameter increase with the increase of Cr doping concentration. The morphology of the samples exhibits irregular spherical or ellipsoid particles with uniform particle size. XEDS spectra display Cr3+ successfully used as doping agent replaced Zn2+ and entered ZnAl2O4 matrix. XPS spectra demonstrate that the doped Cr ions mainly occupy the tetrahedral sites in Zn0.95Cr0.05Al2O4 sample. UV-vis spectra indicate the band gap of the doped sample decrease and exhibit red shift with the increase of Cr ion concentration. The intensity of FT-IR spectra for Zn1-xCrxAl2O4 samples decreases slowly and occurs red shift. PL spectra show the intensity decrease and occur luminescence quenching phenomenon for Cr doped sample.