Photoluminescence of Laser-Synthesized Anatase Titanium Dioxide Nanopowders

Abstract

Titanium dioxide (TiO2) nanopowders were prepared by laser-induced pyrolysis. Raman scattering showed that prepared TiO2 nanocrystals have anatase TiO2 structure. Specific surface area of the powders varies from 84 to 110 m2/g, while the grain size of nanoparticles is between 30 and 70 nm, depending on preparation conditions. We measured photoluminescence (PL) spectra of TiO2 nanocrystals. Under laser irradiation with photon energy between 2.41 and 2.71 eV the TiO2 nanocrystals displayed strong visible light emission, even at excitation power as low as 0.05 W/cm2. The line shape and position of this broad luminescence band vary with excitation energy. As PL spectra of anatase TiO2 can be attributed to three kinds of physical origins (self-trapped excitons, surface states and oxygen vacancies) in this paper we try to resolve which of them are dominant for different TiO2 nanopowders of different grain size.

Optical Characterization of Laser-Synthesized Anatase TiO2Nanopowders by Spectroscopic Ellipsometry and Photoluminescence Measurements

“…Raman measurements also confirmed that both investigated TiO 2 nanocrystals had an anatase structure [6].…”

“…However, excitation of the sample with smaller nanocrystallites, TiS57, by higher photon energies (2.71 eV, close enough to the energy bandgap) activates selftrapped exciton luminescence [1,6]. With temperature decrease, the PL intensity in the sample TiS57 increases and the band maximum position is redshifted from ≈ 2.30 eV at room temperature to ≈ 2.24 eV at 20 K (Fig.…”

“…The energy of these optical electron transitions is about 2.2 eV [1,6]. However, excitation of the sample with smaller nanocrystallites, TiS57, by higher photon energies (close enough to the energy band gap) activates self-trapped exciton luminescence with the energy of ≈ 2.41 eV [4] (and the references therein).…”

Photoluminescence of nanocrystalline titanium dioxide films loaded with silver nanoparticles

“…18 The PL due to the subgap energy states can be excited with a photon energy that is lower than the TiO 2 bandgap energy; the emission spectrum changes with the excitation energy, 26,27 and this PL is very weakly sensitive to the ambient air atmosphere. In the visible spectrum interval, the nc-TiO 2 exhibits two dominant PL features of different origin: (1) radiative recombination of the selftrapped exciton and (2) radiative transitions within subgap states originating from the surface.…”

Nanocrystalline titanium dioxide films: Influence of ambient conditions on surface- and volume-related photoluminescence

“…However, the physics of this interaction is still not well understood on the microscopic level. [10][11][12][13][14][15] The most common way to study the surface related PL of nc-TiO 2 is to use the sub band gap ͑Ͻ3.2 eV͒ energy photons for the photoexcitation. The interpretation of the experimental results is difficult due to variety in material properties.…”