  Anatase TiO2 is an indirect band-gap material with large degree of
sub-stoichiometry, selective excitation of its native defect reveals
polychromatic emission in blue, green and red spectral regions due to self
trapped excitons and singlet-singlet transition of defect states. Electron spin
resonance measurement in dark shows presence of isolated Ti+3, deep lying, and
surface lying VO at 1.986, 2.04 and 2.023 g values respectively, whereas , on
exposure with visible light in situ ESR measurement reveals the formation of
defect complex of Ti+3-VO and Ti+4-V+O.
