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Abstract: The optical absorption and photoluminescence of anatase and rutile TiO2 were studied at room temperature. TiO2 nanocrystalline powders were synthesized in the form of pure anatase or rutile. The samples were characterized by X-ray diffraction, X-ray fluorescence, Raman spectroscopy, optical absorption and photoluminescence (PL) methods. The PL spectra were studied under the intensive UV (3.68eV) laser excitation. Some interesting features in the PL spectra including the well-resolved peaks of excitonic and band–band transitions in TiO2 were observed, to our knowledge, for the first time. It is shown that PL bands including peaks at 2.71–2.81eV and its phonon replicas in anatase and rutile TiO2 arise from the excitonic e −−h + recombination via oxygen vacancies. The excitonic peak at 2.91eV is attributed to the recombination of self-trapped excitons in anatase or free excitons in rutile TiO2. The PL peaks within 3.0–3.3eV in anatase TiO2 are ascribed to indirect allowed transitions due to the band–band e −−h + recombination. The peaks at 3.03eV and 3.26eV are attributed to the free exciton emission near the fundamental band edge of rutile and anatase TiO2, respectively. The influence of TiO2 crystal structure and calcination temperature on the PL spectra is discussed. [Copyright &y& Elsevier]

The optical absorption and photoluminescence of nanocrystalline TiO2 samples of anatase and rutile were investigated at room temperature. Nanocrystalline TiO2 samples were synthesized in the form of pure anatase or rutile and studied by X-ray diffraction, X-ray fluorescence, Raman spectroscopy, optical absorption and photoluminescence (PL). PL was studied at room temperature when excited by intense UV (3.68 eV) by a nitrogen laser. For the first time for nanocrystalline TiO2 a features in the high-resolution PL spectra, including the exciton band and interband transitions were registered. It is concluded that the processes of absorption and emission of light near the edge of the forbidden zone occur with the participation of the same electronic transitions. PL bands, including the peaks at 2.71-2.81 eV in the anatase and rutile arise due to exciton recombination in the TiO2 lattice oxygen vacancies. The exciton peak at 2.91 eV is attributed to the recombination of self-trapped excitons in anatase or to the free exciton in rutile, respectively. PL bands within 3.0-3.3 eV attributed to indirect and direct allowed transitions due to electron-hole recombination. PL bands at 3.03 eV and 3.26 eV, attributed to the emission of free excitons near the fundamental absorption edge of rutile and anatase, respectively. The influence of TiO2 crystal structure and calcination temperature of the samples on the PL spectra and optical absorbtion is discussed. [ABSTRACT FROM AUTHOR]

Abstract: The effect of nanocrystalline TiO2 doping with transition metal cations (Cu2+, Fe3+, Co2+, Cr3+) on their optical absorption and photocatalytic properties was investigated. The obtained metal-doped TiO2 samples were characterized by X-ray diffraction, scanning electron microscopy, and UV–vis absorption spectroscopy. It is shown that doping effect on anatase (A) and rutile (R) properties is quite different, being much stronger and complicated on A than on R. Contrary to doped R, doped A revealed a significant red shift of the absorption edge along with the band gap narrowing. Photocatalytic activity of anatase increases upon doping in the order: AR/Co>R/Cu>R/Fe>R/Cr, indicating the inhibitory effect of impurity cations. This fact correlates with the decrease in the UV absorption of the doped rutile in the region of the Hg-lamp irradiation at 4.88eV. [Copyright &y& Elsevier]

We have investigated the effect of doping of nanocrystalline TiO2 with transition metal cations (Cu2+, Fe3+, Co2+ and Cr3+) on the properties related to optical absorption. The metal-doped TiO2 samples obtained by us have been characterised using an X-ray diffractometry, X-ray fluorescence analysis, a scanning electron microscopy, and a UV-visible absorption spectroscopy. It has been shown that the doping effects on the properties of anatase and rutile are quite different, being much stronger and complicated in the case of anatase. The anatase doped with Fe and Cr cations reveals a 'red' shift of the absorption edge and narrowing of the bandgap. [ABSTRACT FROM AUTHOR]