Light excitation of Tb3+in POCl3:SnCl4at 368plusmn;1 and 353plusmn;1 nm leads to fluorescence emission arising from both the5D3and the5D4states of Tb3+, respectively. The5D4state is populated via the5D3state exclusively, by means of the5D3rarr;5D4transition. The appropriate transition probability depends upon adjacent Tb3+ions in their ground state (selfhyphen;quenching,kq) and upon interactions between the5D3state and the solvent (ks). The ratio of the intensities of the fluorescence emission arising from the5D3and5D4states, monitored at 437plusmn;1 nm (5D3rarr;7F4), 491plusmn;1 nm (5D4rarr;7F6) and 545plusmn;1 nm (5D4rarr;7F5), respectively, varies linearly with lsqb;Tb3+rsqb;. Such fluorescence intensity ratios were employed to determinekq/ksand subsequently to obtain the value ofks. At room temperatureksis equal to 630plusmn;10 secminus;1. The depopulation process of the5D4state of Tb3+is independent of the solvent.
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