NIR luminescence of a visible-light-sensitized neodymium complex with large experimental fluorescence branching ratio fo
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ao Chen Department of History of Science and Technology and Archaeometry, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China (Received 24 September 2010; accepted 28 January 2011)
In this work, a visible-light-sensitized neodymium complex with 2-(N,N-diethylanilin-4-yl)-4,6-bis (3,5-dimethylpyrazol-1-yl)-1,3,5-triazine (Dpbt) as a synergetic ligand is synthesized and incorporated into poly(methyl methacrylate) (PMMA). Absorption and luminescent spectra of Nd(TTA)3Dpbt (TTA 5 thenoyltrifluoroacetonate) in PMMA are measured and compared with common complex Nd(TTA)3Phen (Phen 5 1,10-phenanthroline). As a result, Nd(TTA)3Dpbt has relatively high luminescent intensity and wide excited spectral range, attributed to the sensitization of the ligand Dpbt. Judd–Ofelt analysis is used, and Judd–Ofelt parameters are calculated (X2 5 33.72 1020 cm2, X4 5 11.52 1020 cm2, and X6 5 6.81 1020 cm2). The radiative properties are predicted and compared with other different Nd complexes. The stimulated emission cross-section of 4 F3/2/4I11/2 transition is 3.02 1020 cm2 and the estimated lifetime is 506 ls using the Judd–Ofelt parameters. Experimental fluorescence branching ratio of this transition is quite high for Nd ions. The radiative properties’ investigation for 4F3/2/4I11/2 transition indicates that it is possible to be a laser transition.
I. INTRODUCTION
Organic rare earth complexes, which display unique luminescent properties such as long luminescence lifetimes, large Stokes shifts, and sharp emission peaks, are of high interest. Thereinto, optical materials containing rare earth ions like Nd, Er, and Yb with near-infrared (NIR) emission have frequently been studied recently because of their potential applications in the following fields: (i) probes in bioanalysis and bioimaging,1 (ii) active dopants for laser materials or waveguide amplifiers,2,3 (iii) light conversion molecular devices, for example, luminescent solar concentrators.4 It is known that the extinction coefficients of rare earth ions are quite low for the intra-4f transitions that are forbidden. But, in rare earth complexes, chromophores are introduced as “antennae,” which act as energy donors with large absorption cross-sections. In terms of NIR emitting complexes, energy transfer efficiencies are usually dissatisfactory because of the large energy gap between the high excited state levels of chromophores and a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.64 J. Mater. Res., Vol. 26, No. 12, Jun 28, 2011
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relatively low emitting levels of rare earth ions. So the ligands with low exited state levels are required to sensitize the NIR emitting ions. Shifting the absorption band of chromophores to visible light is an effective way to lower the energy level. At the same time, by introducing visible light absorbing ligand, the complexes will have some advantages in practical application. For example, different from ult
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