Journal
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY
Volume 10, Issue 3, Pages 1482-1494Publisher
AMER SCIENTIFIC PUBLISHERS
DOI: 10.1166/jnn.2010.2034
Keywords
Rare-Earths; Anatase TiO2; Luminescence; Nanocrystals
Categories
Funding
- Chinese Academy of Sciences (CAS)
- Instrument Developing Project of CAS [YZ200712]
- NSFC [10504032, 10774143]
- National High-Tech R&D Program of China [2009AA03Z430]
- 973 program [2007CB936703]
- Fujian Provincial Science Fund for Distinguished Young Scholars [2009J06030]
- Key Project of Science and Technology of Fujian Province [200710024]
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Trivalent rare-earth (RE3+) ion-doped TiO2 nanophosphors belong to one kind of novel optical materials and have attracted increasing attention. The luminescence properties of different RE3+ ions in various TiO2 nanomaterials have been reviewed. Much attention is paid to our recent progresses on the luminescence properties of RE3+ (RE = Eu, Er, Sm, Nd) ions in anatase TiO2 nanoparticles prepared by a sol-gel-solvothermal method. Using Eu3+ as a sensitive optical probe, three significantly different luminescence centers of Eu3+ in TiO2 nanoparticles were detected by means of site-selective spectroscopy at 10 K. Based on the crystal-field (CF) splitting of Eu3+ at each site, C-2v and D-2 symmetries were proposed for Eu3+ incorporated at two lattice sites. A structural model for the formation of multiple sites was proposed based on the optical behaviors of Eu3+ at different sites. Similar multi-site luminescence was observed in Sm3+- or Nd3+-doped TiO2 nanoparticles. In Eu3+-doped TiO2 nanoparticles, only weak energy transfer from the TiO2 host to the Eu3+ ions was observed at 10 K due to the mismatch of energy between the TiO2 band-gap and the Eu3+ excited states. On the contrary, efficient host-sensitized luminescences were realized in Sm3+- or Nd3+-doped anatase TiO2 nanoparticles due to the match of energy between TiO2 band-gap and the Sm3+ and Nd3+ excited states. The excitation spectra of both Sm3+- and Nd3+-doped samples exhibit a dominant broad peak centered at similar to 340 nm, which is associated with the band-gap of TiO2, indicating that sensitized emission is much more efficient than direct excitation of the Sm3+ and Nd3+ ions. Single lattice site emission of Er3+ in TiO2 nanocrystals can be achieved by modifying the experimental conditions. Upon excitation by a Ti: sapphire laser at 978 nm, intense green upconverted luminescence was observed. The characteristic emission of Er3+ ions was obtained both in the ultraviolet-visible (UV-vis) and near-infrared regions through the high-resolution experiments at 10 K. The CF experienced by Er3+ in TiO2 nanocrystal was systematically studied by means of the energy level fitting.
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