Characterization Of Semiconductor Photocatalysts By Photoluminescence Spectroscopy

Photoluminescence spectroscopy is a very powerful technique for the characterization of the electronic states, optical and photochemical properties of semiconductors, etc. The study of semiconductor photocatalysts by the photoluminescence spectroscopy can not only give the information of defect states in semiconductors, but also the information of transfer, trapping and separating of the photogenerated charge carriers. These information is extremely important for us to understand the complicated mechanism of photocatalytic reactions.In this dissertation, the semiconductor photocatalysts of TiO2, NaTaO3 and ZnxCd1-xS are studied by the photoluminescence spectroscopy. The relations of the photoluminescence properties of TiO2 with its crystal structures are clarified f. Anatase TiO2 displays a visible luminescence band centered at 505 nm and rutile TiO2 mainly shows a near-infrared luminescence band centered at 835 nm, which are respectively ascribed to the oxygen vacancies in anatase TiO2 and the intrinsic defects in rutile TiO2. The excited electrons trapped in the oxygen vacancies of anatase are facilely transferred to Pt deposited on the surface of TiO2 to contribute to the photo-assisted reaction, but the electrons transfer from the intrinsic defects of rutile to Pt deposited on the surface of TiO2 are not observed. The photoluminescence properties of NaTaO3 are sensitive to its defect states, and its photocatalytic activities are also influenced by these defect states. The luminescence features of NaTaO3 synthesized under different conditions are studied and the origins of these emissions are discussed. The high-quality andhigh-quantum-yield ZnxCd1-xS nanocrystals are synthesized by a facile and mild approach involved in precipitable-hydrothermal processes. With the increase of Zn molar fraction, the absorption band onsets, near band edge luminescence and deep level luminescence systematically shift from the longer wavelength for CdS to the shorter wavelength for ZnS.As the semiconductor particle size decreases, its optical properties of the particle, such as bandgap and photoluminescence lifetime, are usually changed due to the quantum effect. The special optical properties of semiconductor clusters confined in pores of micro-zeolites are also investigated by the steady-state and time-resolved photoluminescence spectroscopy. The ZnO, ZnS and TiO2 semiconductor clusters confined in micropore zeolites (HZSM-5, HBeta, etc.) show the significantly different optical behaviors from their bulk material, for example, the blue-shifts of the absorption onset and the luminescence bands. The microsecond luminescence lifetime of ZnO clusters is observed at room temperature, which is significantly affected by the electron-phonon interaction between ZnO clusters and zeolite host. The long-lived luminescence of ZnO clusters can be obtained by controlling ZnO loadings and reducing the coupling of electronic transition from ZnO to host phonons of zeolites.