Fluorescence Enhancement of Tb~(3+)in the Tb~(3+)-Trimesic Acid-Gd~(3+)Complex: Role of Polynuclear Structures

摘要

The mechanism of fluorescence enhancement of Tb3+ in Tb3+-trimesic acid-Gd3+ systems has been explored using dynamic light scattering.In earlier work,the mechanism of fluorescence enhancement of Tb~(3+)in these systems was proposed to be due to the formation of a polynuclear complex involving Tb~(3+),trimesic acid and Gd~(3+).However,no direct experimental evidence was presented for the mechanism in that work.In this work,we have used dynamic light scattering(DLS),to measure changes in the mean hydrodynamic diameter(Z_(avg))of the Tb3+-trimesic acid-Gd3+ complex,as a function of time.The Z_(avg)was found to increase monotonically as a function of time,indicating a continuous growth in the particle size.The Eu3+-β-diketones-Gd~(3+)system also shows enhancement of Eu~(3+)fluorescence;though a different mechanism was believed to be operating in this case;namely intermolecular energy transfer.If the two systems followed different mechanisms for fluorescence enhancement,the Eu3+-β-diketones-Gd~(3+)system,is expected to show a different time evolution of particle size.The DLS study showed that the Zavg increased rapidly to a maximum value and then remained nearly constant throughout our measurements;that is,no gradual increase in Z_(avg)was seen as in the Tb~(3+)-trimesic acid-Gd~(3+)system.These DLS studies of the Tb~(3+)-trimesic acid-Gd~(3+)and Eu3+-β-diketones-Gd3+ systems,therefore confirms that different mechanisms of fluorescence enhancement are operative in the two systems.