Sm3+ doped TiO2 as optical oxygen sensor material

• Nanostructural TiO2 based material is proposed for optical oxygen sensing.
• Luminescence lifetime based sensing with rare earth emission is demonstrated.
• Mechanism of oxygen sensing – electronically switched energy transfer – is proposed.

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.