Influence of annealing on the structural, optical and photoluminescence properties of TiO2 nanoparticles

TiO2 nanoparticles were synthesized by co-precipitation method and annealed at 500°C and 700°C in air. The samples were characterized by powder X-ray diffractometry (XRD), Raman, UV-Vis-NIR and Photoluminescence spectroscopic measurements.XRD and Raman analysis confirmed that both the samples possess single phase anatase type tetragonal structure. The average crystallite size of the 500°C and 700°C annealed TiO2 nanoparticles were estimated to be 10±3 and 14±4 nm respectively. Optical absorption study showedthat in both the samples maximum photo absorption take place below 400 nm and the band gap energy were found to be 2.87 (±0.2) eV and 2.37 (±0.3) eV for 500°C and 700°C respectively. Photoluminescence spectrums of the two samples displayed strong emission in the visible band with multiple electronic transitions in the 400-850nm range, which suggests presence of various types of lattice defects in the TiO2 matrix. Increase in annealing temperature leads to red shifting of the visible band and reduction of band gap energy. Computed values of CCT were found to be 1992K and 1980K for 500°C and 700°C respectively, which makes them suitable material for the light harvesting optoelectronic devices.