Influence of annealing temperature on the structural and optical properties of nanocrystalline zirconium oxide

Nanocrystalline zirconium oxide powder was prepared by sol-gel method using zirconyl chloride octahydrate (ZrOCl2·8H2O) and ethylenediaminetetraacitic acid (EDTA) in ammonium hydroxide (NH4OH) solution. The as-synthesized complex product was annealed at 650 °C, 750 °C and 850 °C for 2 h to get fine ZrO2 powder. These samples were further analyzed by Scanning electron microscopy (SEM), X- ray diffraction (XRD), Energy-dispersive X- ray spectroscopy (EDX), UV-vis analysis, Fourier transform infrared (FT-IR) spectroscopy, Photoluminescence spectroscopy (PL) and Raman Spectroscopy to study their structural and optical properties. The structural studies revealed that nanocrystalline ZrO2 powder exhibits monoclinic phase with variation in crystallite size with annealing temperature. The UV-vis absorption band edge of ZrO2 decreases from 514 nm to 451 nm as annealing temperature rises from 650 °C to 750 °C. It seems that the drastic reduction in band gap energy may be one of the novel unexpected characteristics of ZrO2. The FTIR analyses further confirmed the formation of nanocrystalline monoclinic ZrO2. PL analysis revealed the novel emission peaks at 305 and 565 nm. The Raman spectroscopy confirmed the transformation of amorphous zirconium hydroxide to m-ZrO2 with increase in temperature from 650 °C to 850 °C.