Tailoring luminescence properties of TiO2 nanoparticles by Mn doping

TiO2 nanoparticles are doped with three different concentrations of Mn, 2%, 4% and 6% respectively. Absorption edge of TiO2 is shifted from UV to visible region on amplification of Mn content. Room temperature photoluminescence spectra, excited at 320 nm, exhibit band edge and visible emission peaks associated with self trapped excitons, oxygen defects, etc. Doping of Mn increases the width and decreases the intensity of the UV emission peak. Potential fluctuations of impurities increase the width and auger type non-radiative recombination decreases the intensity of the UV emission peak. The intensity ratio of the UV to defect emission band decreases on doping, indicating degradation of structural quality. Excitation of pure and doped nanoparticles at 390 nm results in Mn2+ emission peaks at 525 nm and 585 nm respectively. Photoluminescence excitation spectra also indicate the presence of Mn2+ in the crystalline environment of TiO2. The oxygen defects and Mn related impurities act as efficient trap centers and increases the lifetime of the charge carriers.