Optical properties and theoretical study of Mn doped ZnAl2O4 nanoparticles with spinel structure

Zn1-xMnxAl2O4 (x = 0, 0.10, 0.20, 0.30 and 0.40) nanoparticles were synthesized by hydrothermal method, and the effects of Mn doping on the microstructure, morphology, binding energy and optical property of the samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), x-ray photoemission spectroscopy (XPS), ultraviolet–visible (UV–Vis) spectroscopy, photoluminescence spectra (PL) and fourier transform infrared spectroscopy (FT-IR). And the energy band structure of various defects in ZnAl2O4 structure were calculated by means of the first-principles calculations. The experimental results show that Zn1-xMnxAl2O4 nanoparticles possess cubic spinel structure without other impurity phases. The morphology of the samples exhibits irregular spherical or ellipsoid particles with uniform particle size. EDX Mapping display that Zn, Al, O and Mn elements are uniformly distributed without any enrichment phenomenon throughout the sample. Mn ions successfully used as doping agent replaced Zn2+ and entered ZnAl2O4 matrix. Combined with the calculated results of the first principle calculations, the substitution of Mn introduced new energy levels, which level make the intensity of PL spectra decrease and occur quenching phenomenon. XPS spectra demonstrate that the doped Mn ions mainly occupy the tetrahedral sites. UV–vis spectra indicate with the increase of Mn ion concentration, the band gap of the doped sample decrease with the increase of Mn content and exhibit red shift. FT-IR show that all Mn2+ ions substituted for Zn2+ ions without changing ZnAl2O4 spinel structure.