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

Abstract

Some nanocrystalline TiO 2 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 TiO 2 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 O 2 /N 2 flow. Sm 3+ :TiO 2 worked effectively at room temperature, whereas Nd 3+ :TiO 2 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 O 2 and recovery time of 10 min in N 2 . The PL decay kinetics of Sm 3+ :TiO 2 showed unambiguously that both decreasing O 2 concentration and increasing temperature reduced the fluorescence quantum yield of excited Sm 3+ ions. Such behavior is compatible with the proposed model of energy acceptors created by (reversible) electron transfer from desorbed charged O 2 species to certain lattice defects. In contrast, decreasing O 2 concentration increased the PL intensity of Nd 3+ :TiO 2 . In this case, PL decay kinetics showed an increased excitation efficiency of Nd 3+ ions, suggesting that O 2 adsorption favors a concurrent relaxation path for the photoexcited charge carriers.

Optically Active TiO2:Er Thin Films Deposited by Magnetron Sputtering

“…Titanium dioxide doped with lanthanide Ln-ions exhibits well-pronounced photoluminescence in the visible range of the light spectrum [ 20 , 21 , 22 , 23 , 24 ]. Numerous reports on the application of such nanomaterials in photoelectrochemical cells and photocatalytic decomposition of organic pollutants were published recently [ 25 , 26 , 27 ].…”

Extraction–Pyrolytic Method for TiO2 Polymorphs Production

“…To reduce the bandgap, TiO 2 should be either doped (e.g., with N, Ta) or used in the form of nanotubes [13,[21][22][23][24][25][26]. Other important studies are related to the applications of TiO 2 as protective coatings in microelectronic and optical devices and as luminescent compounds [27][28][29][30][31][32]. TiO 2 forms three naturally occurring polymorphic crystalline modifications in the form of the corresponding minerals: brookite with rhombic, anatase and rutile with a tetragonal crystal lattice [1,4,33].…”

Mesoporous TiO2 from Metal-Organic Frameworks for Photoluminescence-Based Optical Sensing of Oxygen

“…The detection of gaseous oxygen (O 2 ) in gas mixtures and/or aqueous environments is important for many of applications, such as air quality control, packaging, life sciences, and automotive and chemical industry [1][2][3][4].…”