Sm3+ doped TiO2 as optical oxygen sensor material

The luminescence properties of Sm³⁺ in sol-gel-made nanostructural TiO₂ were shown to depend on surrounding gas environment. Both the intensity and lifetime of the luminescence increased with increasing oxygen content varied between 0% and 100% in the O₂/N₂ mixture at normal pressure. The luminescence decay kinetics after pulsed excitation at 355 nm followed the stretched exponential function with the value of stretching exponent equal to 0.4-0.5. The mechanism of oxygen sensitivity was interpreted as resonant excitation energy transfer from Sm³⁺ to the acceptor defects, the latter being switched on and off the resonance by electron exchange with surface-adsorbed oxygen. Oxygen vacancy related defects were proposed as most likely candidates of energy acceptors. The studied material can be used for luminescence lifetime based oxygen sensing.