Quenching of Tb 3+photoluminescence by solvated electron in liquid ammonia

The photoluminescence of terbium(III) chloride in liquid ammonia at 293 K and 8.8 atm is considered. The solubility of TbCl 3 crystal hydrate in ammonia is 5 center dot 10 -4 mol/L. The luminescence spectrum of the solvated Tb 3+ ion in this solution coincides with the luminescence spectrum of the hydrated Tb 3+ ion in a similar aqueous solution at atmospheric pressure. The measured excited state ( 5 D 4 ) lifetime tau of the terbium ion is somewhat longer in ammonia (470 mu s) than in water (420 mu s). The (Tb 3+ )* luminescence in ammonia is quenched by solvated electron (e s - ), formed upon dissolution of lithium metal. Under these conditions, a solution of Tb 3+ and e s - is unstable, precipitate is being formed, and continuous change in the component concentrations takes place. This hampers obtaining an adequate Stern-Volmer dependence of the Tb 3+ luminescence intensity on the concentration of the quencher e s - , which is determined by measuring the absorbance of the solution at 1400 nm at the absorption band of e s - . A linear dependence was obtained by measurement of terbium ion tau with variable e s - concentration. The results were used to calculate the bimolecular rate constant k = (3.2 +/- 0.3)center dot 10 8 M - 1 s - 1 for the assumed quenching reaction (Tb 3+ )* + e s - -> Tb 2+ .