Water as probe molecule for midgap states in nanocrystalline strontium titanate by conventional and synchronous luminescence spectroscopy under ambient conditions
Abstract Alkaline earth metal titanates are broad bandgap semiconductors with applications in electronic devices, as catalysts, photocatalysts, sorbents, and sensors. Strontium titanate SrTiO 3 is of interest in electronic devices, sensors, in the photocatalytic hydrogen generation, as catalyst and sorbent. Both photocatalysis and operation of electronic devices rely upon the pathways of relaxation of excited charge in the semiconductor, including relaxation through the midgap states. We report characterization of nanocrystalline SrTiO 3 at room temperature by “conventional” vs. synchronous luminescence spectroscopy and complementary methods. We determined energies of radiative transitions in the visible range through the two midgap states in the nanocrystalline SrTiO 3 . Further, adsorption and desorption of vapor of water as “probe molecule” for midgap states in the nanocrystalline SrTiO 3 was studied, for the first time, by luminescence spectroscopy under ambient conditions. Emission of visible light from the nanocrystalline SrTiO 3 is significantly increased upon desorption of water and decreased (quenched) upon adsorption of water vapor, due to interactions with the surface midgap states. Highlights Photoluminescence, reflectance, Raman spectra and XRD are reported for nanoSrTiO 3 . The energy diagram for charge photoexcitation and emission is determined at 25°C. Energies of optical emission through the two midgap states in nanoSrTiO 3 are found. Synchronous luminescence spectra at 25°C are narrower than conventional spectra. Adsorption of water vapor on nanoSrTiO 3 causes reversible PL quenching. Graphical Abstract [DISPLAY OMISSION]
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