Title: Defect‐Mediated Photoluminescence Dynamics of Eu<sup>3+</sup>‐Doped TiO<sub>2</sub> Nanocrystals Revealed at the Single‐Particle or Single‐Aggregate Level
Abstract: Angewandte Chemie International EditionVolume 47, Issue 29 p. 5348-5352 Communication Defect-Mediated Photoluminescence Dynamics of Eu3+-Doped TiO2 Nanocrystals Revealed at the Single-Particle or Single-Aggregate Level† Takashi Tachikawa Dr., Takashi Tachikawa Dr. The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047 (Japan), Fax: (+81) 6-6879–8499 http://www.sanken.osaka-u.ac.jp/labs/mec/index.htmlSearch for more papers by this authorTakamasa Ishigaki Prof. Dr., Takamasa Ishigaki Prof. Dr. National Institute for Materials Science, Nano Ceramics Center, Namiki 1-1, Tsukuba, Ibaraki 305-0044 (Japan)Search for more papers by this authorJi-Guang Li Dr., Ji-Guang Li Dr. National Institute for Materials Science, Nano Ceramics Center, Namiki 1-1, Tsukuba, Ibaraki 305-0044 (Japan)Search for more papers by this authorMamoru Fujitsuka Prof. Dr., Mamoru Fujitsuka Prof. Dr. The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047 (Japan), Fax: (+81) 6-6879–8499 http://www.sanken.osaka-u.ac.jp/labs/mec/index.htmlSearch for more papers by this authorTetsuro Majima Prof. Dr., Tetsuro Majima Prof. Dr. [email protected] The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047 (Japan), Fax: (+81) 6-6879–8499 http://www.sanken.osaka-u.ac.jp/labs/mec/index.htmlSearch for more papers by this author Takashi Tachikawa Dr., Takashi Tachikawa Dr. The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047 (Japan), Fax: (+81) 6-6879–8499 http://www.sanken.osaka-u.ac.jp/labs/mec/index.htmlSearch for more papers by this authorTakamasa Ishigaki Prof. Dr., Takamasa Ishigaki Prof. Dr. National Institute for Materials Science, Nano Ceramics Center, Namiki 1-1, Tsukuba, Ibaraki 305-0044 (Japan)Search for more papers by this authorJi-Guang Li Dr., Ji-Guang Li Dr. National Institute for Materials Science, Nano Ceramics Center, Namiki 1-1, Tsukuba, Ibaraki 305-0044 (Japan)Search for more papers by this authorMamoru Fujitsuka Prof. Dr., Mamoru Fujitsuka Prof. Dr. The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047 (Japan), Fax: (+81) 6-6879–8499 http://www.sanken.osaka-u.ac.jp/labs/mec/index.htmlSearch for more papers by this authorTetsuro Majima Prof. Dr., Tetsuro Majima Prof. Dr. [email protected] The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047 (Japan), Fax: (+81) 6-6879–8499 http://www.sanken.osaka-u.ac.jp/labs/mec/index.htmlSearch for more papers by this author First published: 07 July 2008 https://doi.org/10.1002/anie.200800528Citations: 75 † This work has been partly supported by a Grant-in-Aid for Scientific Research (Project 17105005 and others) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japanese Government. T.T. is thankful for partial support from the Iketani Science and Technology Foundation. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Graphical Abstract Single-particle fluorescence spectroscopy was used to investigate defect-mediated photoluminescence (PL) dynamics of undoped and Eu3+-doped TiO2 nanoparticles, and revealed that free excitons in the photoirradiated TiO2 host can excite both interior and surface Eu3+ ions, while trapped excitons at the surface only excite the latter. The picture shows PL images of TiO2:Eu3+ nanoparticles during laser excitation in air and argon atmospheres. Supporting Information Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2008/z800528_s.html or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. References 1For example, G. Blasse, B. C. Grabmaier in Luminescent Materials, Springer, Berlin, 1994. 2 2aA. Conde-Gallardo, M. García-Rocha, I. Hernández-Calderón, R. Palomino-Merino, Appl. Phys. Lett. 2001, 78, 3436–3438; 2bK. L. Frindell, M. H. Bartl, M. R. Robinson, G. C. Bazan, A. Popitsch, G. D. Stucky, J. Solid State Chem. 2003, 172, 81–88; 2cC. W. Jia, E. Q. Xie, J. G. Zhao, Z. W. Sun, A. H. Peng, J. Appl. Phys. 2006, 100, 023529; 2dJ.-G. Li, X. Wang, K. Watanabe, T. Ishigaki, J. Phys. Chem. B 2006, 110, 1121–1127, and references therein. 3 3aS. A. Empedocles, M. G. Bawendi, Science 1997, 278, 2114–2117; 3bK. T. Shimizu, R. G. Neuhauser, C. A. Leatherdale, S. A. Empedocles, W. K. Woo, M. G. Bawendi, Phys. Rev. B 2000, 63, 205316; 3cR. E. Palacios, F.-R. F. Fan, J. K. Grey, J. Suk, A. J. Bard, P. F. Barbara, Nat. Mater. 2007, 6, 680–685. 4 4aM. D. Barnes, A. Mehta, T. Thundat, R. N. Bhargava, V. Chhabra, B. Kulkarni, J. Phys. Chem. B 2000, 104, 6099–6102; 4bR. Rodrigues-Herzog, F. Trotta, H. Bill, J.-M. Segura, B. Hecht, H.-J. Güntherodt, Phys. Rev. B 2000, 62, 11163–11169; 4cA. P. Bartko, L. A. Peyser, R. M. Dickson, A. Mehta, T. Thundat, R. Bhargava, M. D. Barnes, Chem. Phys. Lett. 2002, 358, 459–465. 5 5aThe volume fraction of total ions on the surface of nanocrystalline TiO2:Eu3+ is calculated by using {[4/3πr3−4/3π(r−δ)3]/4/3πr3}×100, where δ is the assumed surface thickness of 0.4 nm (the length of TiO bonds is 0.196 nm)[5b] and r is the particle radius (5 nm). For example, the volume fraction of total ions at the surface is estimated to be about 22 %; 5bV. Swamy, D. Menzies, B. C. Muddle, A. Kuznetsov, L. S. Dubrovinsky, Q. Dai, V. Dmitriev, Appl. Phys. Lett. 2006, 88, 243103. 6 6aK. Riwotzki, M. Haase, J. Phys. Chem. B 1998, 102, 10129–10135; 6bG. Blasse, Prog. Solid State Chem. 1988, 18, 79–171. 7 7aJ. F. Suyver, R. Meester, J. J. Kelly, A. Meijerink, Phys. Rev. B 2001, 64, 235408; 7bJ. F. Suyver, R. Meester, J. J. Kelly, A. Meijerink, Phys. Rev. B 2002, 66, 079901. 8In fact, no significant concentration quenching was observed in the low concentration range of Eu3+ ions (<0.5 atom %) at the bulk level. At the higher dopant concentrations (>0.5 atom %), however, most of the Eu3+ ions are expelled during the cooling processes of the TiO2 melt droplets because of their very limited solubility in TiO2, and thus Eu2Ti2O7 pyrochlore is formed.[2d] 9J. Grausem, M. Dossot, S. Cremel, B. Humbert, F. Viala, P. Mauchien, J. Phys. Chem. B 2006, 110, 11259–11266. 10R. Helmy, A. Y. Fadeev, Langmuir 2002, 18, 8924–8928. 11Anatase and rutile have site symmetries for Ti4+ of D2d and D2h, respectively. Thus, the substitution of Eu3+ for Ti4+ creates oxygen vacancies and lattice distortions in the TiO2 host which result in the increased asymmetric ratio. The formation of Eu3+-O2−-Ti4+ bonds would increase the degree of covalence between Eu and O, since the Ti4+ ion has a larger radius and lower electronegativity. These structural features may partially explain the observed difference in R. 12 12aSekiya et al. reported that the visible PL spectrum consists of three components centered at about 517, 577, and 636 nm, which are assigned to excitons bound to partially reduced titanium ions, self-trapped excitons through an exciton–lattice interaction, and oxygen vacancies, respectively.[12b,c] See references [12c–e] for lifetimes of the photogenerated charge carriers and trapped species. It is also noteworthy that no PL band in the near-infrared region due to the intrinsic defects from the rutile TiO2 was observed under air and Ar atmospheres, although the present undoped TiO2 and TiO2:Eu3+ powders contain 22 and 31 wt % of rutile, respectively; 12bT. Sekiya, S. Kamei, S. Kurita, J. Lumin. 2000, 87–89, 1140–1142; 12cT. Sekiya, M. Tasaki, K. Wakabayashi, S. Kurita, J. Lumin. 2004, 108, 69–73; 12dN. Serpone, D. Lawless, R. Khairutdinov, E. Pelizzetti, J. Phys. Chem. 1995, 99, 16655–16661; 12eT. Tachikawa, M. Fujitsuka, T. Majima, J. Phys. Chem. C 2007, 111, 5259–5275, and references therein. 13V. N. Kuznetsov, N. Serpone, J. Phys. Chem. C 2007, 111, 15277–15288. 14 14aS. R. Cordero, P. J. Carson, R. A. Estabrook, G. F. Strouse, S. K. Buratto, J. Phys. Chem. B 2000, 104, 12137–12142; 14bY. Wang, Z. Tang, M. A. Correa-Duarte, L. M. Liz-Marzán, N. A. Kotov, J. Am. Chem. Soc. 2003, 125, 2830–2831; 14cT. Uematsu, S. Maenosono, Y. Yamaguchi, J. Phys. Chem. B 2005, 109, 8613–8618; 14dS. F. Lee, M. A. Osborne, J. Am. Chem. Soc. 2007, 129, 8936–8937. 15 15aThe quantum yields for the generation of O2.− and 1O2, which is most probably generated by the charge-recombination reaction between O2.− and photogenerated holes, are reported to be about 0.4[15b] and 0.2–0.3,[15c] respectively, for various TiO2 photocatalysts in air; 15bK. Ishibashi, A. Fujishima, T. Watanabe, K. Hashimoto, J. Phys. Chem. B 2000, 104, 4934–4938; 15cT. Daimon, Y. Nosaka, J. Phys. Chem. C 2007, 111, 4420–4424. 16 16aUnfortunately, we cannot perform more quantitative analysis, because there is no report of the absorption cross-section and PL quantum yield of color centers. For the intrinsic absorption of TiO2, however, the excitation rate (kex) is roughly estimated to be about 105 s−1 according to the following equation: kex=Nph⋅σ, where Nph is the number of photons (1×1021 cm−2 s−1) and σ is the absorption cross-section (5×10−17 cm2). Here, the σ value is obtained from σ=kabs⋅Vparticle, where kabs is the absorption coefficient (102 cm−1, near the band edge of the fundamental absorption of TiO2)[16b] and Vparticle is the particle volume (5×10−19 cm3, r=5 nm); 16bA. V. Emeline, V. K. Ryabchuk, N. Serpone, J. Phys. Chem. B 1999, 103, 1316–1324. 17 17aThe photon energy up-conversion of mid-gap energy levels originating from oxygen vacancies[17b] may be involved in the photoactivation processes; 17bN. D. Abazović, M. I. Čomor, M. D. Dramićanin, D. J. Jovanović, S. P. Ahrenkiel, J. M. Nedeljković, J. Phys. Chem. B 1999, 103, 1316–1324. Citing Literature Volume47, Issue29July 7, 2008Pages 5348-5352 ReferencesRelatedInformation
Publication Year: 2008
Publication Date: 2008-06-11
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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