Photoluminescence study deals important with photocatalysts, in-particularly metal oxide photocatalysts. Information regarding the presence of surface states, formation of photoinduced charge carriers, and their recombination kinetics can be drawn from the photoluminescence (PL) spectra of semiconductor materials [1]. Photoinduced carriers formed in the matrix can undergo the recombination process, which reduce the photocatalytic activity. Carriers can be also intercepted by the trapping center, which allows avoiding the recombination, or taking part in reaction of pollutants decomposition and forming oxidizing compounds. Photocatalytic activity of metal oxides (such as TiO2, ZnO and SnO2) depends directly on amount of generated carriers, but its efficiency is determined by process of separation, recombination, capture, and transfer of carriers to the surface. It results from the fact that all oxidizing and reducing processes take place at the surface of photocatalysts [2-3]. Recently, we reported some papers deals with luminescence effect correlated with photocatalytic efficiency [4-7].
Figure 1 Steady state emission spectra of Sn–Ti-x samples at room temperature [4].
Here I presented one of my reports, which was published in RSC Advances in year 2016. Emission spectra of Sn doped TiO2 nanoparticles with different concentration of Sn (Sn–Ti-x) samples with excitations at 330 nm are presented in Figure 1. A strong green emission was observed at 560 nm (2.22 eV). Therefore, emissions likely originated from surface defects, such as ionizable oxygen vacancies and the recombination of self-trapped excitons (STEs) which are localized within TiO6 octahedra geomentry.
Figure 2 Variation of intensity of emission band, Mr and PDE (phenol degradation) values of Sn–Ti-x with different Sn doping level [4].
The correlation studies performed between PL intensity as well as photodegradation efficiency (PDE) vs different concentration of Sn in TiO2 as shown in Figure 2. The decrease in the PL density at higher Sn doping level was also confirmed by PL spectroscopic results. Oxygen vacancies are found to be the main cause for affect photocatalytic activity of metal oxide nanostructures. These reports mainly conclude that PL spectroscopy investigation deals oxygen vacancies, charge carriers, trapping center and their recombination kinetics of metal oxide photocatalyts.
References
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2. A. Fujishima, X. Zhang, D. A. Tryk, Surface Science Reports, 63 (2008) 515–582.
3. H. Ohsaki, N. Kanai, Y. Fukunaga, M. Suzuki, T. Watanabe, and K. Hashimoto, Thin Solid Films, 502 (2006) 138–142.
4. A. S. Ganeshraja, S. Thirumurugan, K. Rajkumar, K. Zhu, Y. Wang, K. Anbalagan, J. Wang, RSC Adv., 6 (2016) 409-421.
5. A. S. Ganeshraja, A. Clara, K. Rajkumar, Y. Wang, Y. Wang, J. Wang, K. Anbalagan, Appl. Surf. Sci. 353 (2015) 553-563. (Impact Factor = 5.155)
6. A. S. Ganeshraja, K. Rajkumar, K. Zhu, X. Li, S. Thirumurugan, W. Xu, J. Zhang, M. Yang, K. Anbalagan, J. Wang, RSC Adv. 6 (2016) 72791–72802.
7. A. S. Ganeshraja, S. Thirumurugan, K. Rajkumar, J. Wang, K. Anbalagan, J. Alloys Compd., 706 (2017) 485-494.