Oxygen-Sensitive Photoluminescence of Rare Earth Ions in TiO2 Thin Films

Abstract

Some nanocrystalline TiO2 materials are notorious for their photoluminescence (PL), which exhibits a pronounced sensitivity to ambient oxygen and has a potential for optical gas sensing. Here, we utilized pulsed laser deposition to obtain thin (70 nm) anatase TiO2 films containing 1–2 atom % of either samarium (Sm) or neodymium (Nd) impurity ions. The highly porous nanostructure consisted of quite regular, interconnected nanopillars with a wall thickness of 15–20 nm, fully exposing the material to ambient environment. The PL intensity of both ions (induced by 355 nm pulsed laser) responded in a reversible manner to changes of oxygen volume fraction in dry O2/N2 flow. Sm3+:TiO2 worked effectively at room temperature, whereas Nd3+:TiO2 showed an improved relative response at 100–150 °C. Switching between pure nitrogen and oxygen atmospheres affected the PL intensities up to 6 times, with response time of 1 min to O2 and recovery time of 10 min in N2. The PL decay kinetics of Sm3+:TiO2 showed unambiguously t...