Effect of Cr3+ doping on structural and optical property of ZnGa2O4 synthesized by sol gel method

Abstract

Zinc gallate host and chromium ions doped ZnGa2O4 nano-powders was synthesized by citric acid assisted sol-gel method. The dopant molar percentage were varied between (0–2.5 mol. %). The x-ray diffraction (XRD) patterns shown that all synthesized nano powders are cubic structured and doping of Cr3+ ions did not affect the structure at all. The scanning electron microscope micrographs show small particles in nano range that are uniformly distributed, but became agglomerated with high doping of chromium concentrations. The high-resolution transmission electron microscope (HR-TEM) image shows the formation of several agglomerated particles with clear grain boundary and different sizes. Energy dispersive x-ray spectroscopy measurements confirm the presence of the expected elements. Ultraviolet–visible spectrophotometer measurement shows the % reflectance in the UV–vis region to be dependents on Cr3+ ions and the estimated band gap was found to vary between 4.46 and 4.80 eV. Un-doped ZnGa2O4 nano powder displays a broad blue emission but doping with Cr3+ ions caused the emission to occur in the near infrared region. An increase in Cr3+ ions up to 2.0 mol% lead to significantly enhancement in the near infra-red (NIR) emission but decrease thereafter. The CIE color coordinates values located in blue and NIR of the spectrum for undoped and Cr3+ doped samples, respectively. The photoluminescence emission intensity was also observed to be dependent on the excitation wavelength and the emission PL spectrum perfectly match the transparency window of living tissues and can effectively be used for bio imaging application.