DPC03 Chelateposter3

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Information about DPC03 Chelateposter3

Published on January 11, 2008

Author: Sever

Source: authorstream.com

Slide1:  FLUORESCENCE ENHANCEMENT BY CHELATION OF Eu3+ AND Tb3+ IONS IN SOL GELS A. J. Silversmitha A. P. Magyara, K.S. Brewera, and D.M. Boyeb aPhysics Department, Hamilton College, Clinton, NY 13323 USA bPhysics Department, Davidson College, Davidson, NC 28036 USA Chelation of rare earth (RE) ions has been used for many years as a way of enhancing the optical excitation of the ions in solution. The chelating molecules, which absorb strongly in the near uv, bind to the RE ion. Optical excitation of the chelate followed by efficient energy transfer to the RE results in visible fluorescence. In this work we incorporated the chelate-RE complex into sol-gels made with the organic precursor tetramethoxysilane (TMOS). Two chelating agents - 2,6-pyridine-dicarboxylic acid (PDC) and 3-pyridinepropionic acid (PPA) - and two different synthesis techniques are used. Optical properties of the dried gels (heated to 90˚C) and annealed SiO2 doped glasses (heated to 900˚C) were studied to determine firstly, whether the chelate/RE complex remained intact after incorporation into the gel and secondly, whether the optical properties of the annealed glasses differed from those of glasses synthesized without chelation. In addition to studying energy transfer between the chelate molecule and the RE, we investigated whether incorporation of the chelate reduced fluorescence quenching due to residual OH- in the glass – a common problem in RE doped sol-gel glasses. Abstract Conclusions PDC synthesis is effective at isolating the RE within the sol-gel. The synthesis results in enhanced excitation efficiency and reduced fluorescence quenching, resulting in intense red (Eu) or green (Tb) fluorescence under uv excitation. In-situ synthesis with PPA does not result in fully chelated RE ions in gels. Experimental Setup Corresponding author: Dr. Ann Silversmith Physics Department, Hamilton College 198 College Hill Rd. Clinton, NY 13323 asilvers@hamilton.edu This work sponsored in part by the Research Corporation through a Cottrell College Science Award. Sample quality Discussion Very bright green emission from Tb(PDC) dry gels under 254nm excitation Tb(PDC) complex remains intact in sol-gel Terbium behavior mirrors that of Europium, with the addition of the broad 4f8  4f75d1 excitation line in the chelated gels. All syntheses form optically clear gels PDC gels crack and turn powdery after several weeks, but storage with a dessicant helps PDC gels dissintegrate when annealing PPA gels retain good optical clarity upon annealing Other chelating agents, in particular a longer bidentate to replace PPA in the in-situ synthesis. Adjustment of annealing conditions to improve quality of PDC annealed glasses. Fabrication of thin films with chelated RE’s. Synthesis with increased RE concentration. Further Investigation t [ms] ln (fluorescence) 5D07F2 Fluorescence Decays of chelated Eu3+ dry gels Fluorescence Decays of Annealed glasses Fluorescence (arb units) Wavelength (nm) Eu2O3 powder Eu(PDC) glass Eu/Al glass Terbium results t [ms] 5D47F5 Fluorescence Decays Excitation spectra (monitoring 5D47F5 ) Wavelength [nm] 4f8  4f75d1 Discussion Strong Eu3+ excitation band that correlates with the PDC absorption indicates that the Eu(PDC) association remains complete – after incorporation into the gel. Long fluorescence lifetime of Eu(PDC) gel offers further evidence that the chelation is complete. Eu(PDC) samples degrade and are partially opaque after annealing. The fluorescence spectrum has a peak at 611nm, which coincides with the strongest 5D07F2 line in Eu2O3. Fluorescence decay time in Eu(PPA) gels is longer than in Eu/Al gels, indicating partial association of the chelate and Eu3+. The absence of the excitation band for wavelengths below 300nm implies little energy transfer from chelate to Eu3+. The bi-dentate PPA is short and may not be able to bond at two sites. The decay time from Eu(PPA)6 is longer than from Eu(PPA)3 and shorter than Eu(PDC). Further evidence chelation is incomplete in the PPA gels. Incomplete chelation with PPA may be due to the physical size of the molecule - the PPA (bidentate) is a relatively short molecule and may not be long enough to grab on to the RE in two places. The crystalline chelate synthesis ensures that the RE is completely associated; the in-situ technique is a “stir-and-hope” approach. t=0.18ms t=2.3ms t=2.1ms t=1.3ms t=0.83ms ln (fluorescence) Chelate absorption edge Fluorescence (arb units)

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