TEMPERATURE AND SOLVENT EFFECTS UPON THE $^{5}D_{3}\rightarrow^{5}D_{4}$, NONRADIATIVE TRANSITION OF $Tb^{3+}$ IN SOLUTION
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Date
1975
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Ohio State University
Abstract
Ultraviolet light excitation of $Tb^{3+}$ in $POC1_{3}$:$SnC1_{4}$ is accompanied by fluorescence emission arising from the two lowest excited states of $Tb^{3+}$, namely, the $^{5}D_{3}$ and the $^{5}D_{4}$ states. Changes in the temperature and the composition of the solvent bring about pronounced effects upon the emission from the $^{5}D_{3}$ state. The intensity of the fluorescence emission associated with the transition $^{5}D_{3}$ $\rightarrow$ $^{7} F$ increases as the [POC1$_{3}$]/[$SnCl_{4}$] ratio and temperature decrease. A similar effect is observed upon the fluorescence lifetimes of the emission arising from the $^{5}D_{3}$ state of $Tb^{3+}$. This effect is attributed to a very efficient deexcitation process of the $^{5}D_{3}$ state brought about by coupling the nonradiative transition $^{5}D_{3}$ $\rightarrow$ $^{5}D_{4}$ with vibrational transitions in the solvent molecules. The efficiency of this transition is higher in ``protic” organic or inorganic solvents, in which cases no emission from the $^{5}D_{3}$ state of $Tb^{3+}$ has been observed. In the POC1$_{3}$:SnC1$_{4}$ system the highest existing vibrational mode is the one associated with the stretching frequency of the $\rightarrow$ P = 0 group, with a fundamental vibrational frequency of about 1300 $cm^{-1}$. The nonradiative deexcitation of the $^{5}D_{3}$ state by the various overtones of the $\rightarrow$ P = 0 stretching mode can be achieved by $POC1_{3}$ molecules in both the primary and secondary solvation sphere of $Tb^{3+}$. The appropriate deexcitation rate constants were found to be ${k}_^{\prime} = 6 \times 10^{3} \exp(-3400/{RT})$ $sec^{-1}$ and ${k}_{sec} = 2.4 \times 10^{3} \exp (-8500/{RT})$ $M^{-1}$$sec^{-1}$, respectively.
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Author Institution: Department of Chemistry, The University of Toledo