Photoluminescence studies of nitrogen-doped TiO₂ powders prepared by annealing with urea

Abstract

Photoluminescence and excitation spectra have been investigated for undoped and nitrogen-doped TiO₂ powders at low temperatures. A broad luminescence band peaking at 2.25 eV is observed in the undoped TiO₂ powders. The 2.25 eV luminescence band exhibits a sharp rise from 3.34 eV in the excitation spectrum reflecting the fundamental absorption edge of anatase TiO₂. On the other hand, the N-doped TiO₂ powders obtained by annealing with urea at 350 and 500°C exhibit broad luminescence bands around 2.89 and 2.63 eV, respectively. The excitation spectra for these luminescence bands rise from the lower energy side of the fundamental absorption edge of anatase TiO₂. The origin of the luminescence bands and N-related energy levels formed in the band-gap of TiO₂ are discussed.

Keywords:

• anatase TiO₂
• localized states
• luminescence properties
• sol-gel method
• brookite phase
• rutile phase

Acknowledgments

The optical measurements of this work were supported by the Joint Studies Program of the Institute for Molecular Science, Japan.