title: Critical Role of Energy Transfer Between Terbium Ions for Suppression of Back Energy Transfer in Nonanuclear Terbium Clusters.
abstract: Lanthanide (Ln(III)) complexes form an important class of highly efficient luminescent materials showing characteristic line emission after efficient light absorption by the surrounding ligands. The efficiency is however lowered by back energy transfer from Ln(III) ion to the ligands, especially at higher temperatures. Here we report a new strategy to reduce back energy transfer losses. Nonanuclear lanthanide clusters containing terbium and gadolinium ions, TbnGd9-nclusters ([TbnGd9-n(μ-OH)10(butylsalicylate)16]+NO3-, n = 0, 1, 2, 5, 8, 9), were synthesized to investigate the effect of energy transfer between Tb(III) ions on back energy transfer. The photophysical properties of TbnGd9-nclusters were studied by steady-state and time-resolved spectroscopic techniques and revealed a longer emission lifetime with increasing number of Tb(III) ions in TbnGd9-nclusters. A kinetic analysis of temperature dependence of the emission lifetime show that the energy transfer between Tb(III) ions competes with back energy transfer. The experimental results are in agreement with a theoretical rate equation model that confirms the role of energy transfer between Tb(III) ions in reducing back energy transfer losses. The results provide a new strategy in molecular design for improving the luminescence efficiency in lanthanide complexes which is important for potential applications as luminescent materials.
authors.affiliation: Graduate School of Chemical Sciences and Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.
authors.forename: Shun
authors.initials: S
authors.lastname: Omagari
authors.affiliation: Faculty of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Nakanishi
authors.affiliation: Faculty of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Kitagawa
authors.affiliation: Faculty of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Seki
authors.affiliation: Faculty of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Fushimi
authors.affiliation: Faculty of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Ito
authors.affiliation: Debye Institute, Department of Chemistry, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
authors.forename: Andries
authors.initials: A
authors.lastname: Meijerink
authors.affiliation: Faculty of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.
authors.forename: Yasuchika
authors.initials: Y
authors.lastname: Hasegawa