Quenching of gadolinium(III) ion photoluminescence in liquid ammonia by solvated electron

The effect of a solvated electron on the gadolinium(III) chloride photoluminescence in liquid ammonia at 293 K and a pressure of 8.8 atm is considered. The solubility of GdCl₃ crystalline hydrate in ammonia is 5 × 10^–4 M. The solvated Gd³⁺ ion luminescence spectrum thein this solution coincides with the hydrated Gd³⁺ ion luminescence spectrum in a similar aqueous solution at atmospheric pressure. The lifetime τ in the excited state (⁶P_7/2) of the gadolinium(III) ion is longer in ammonia (2.6 ms) than in water (2.0 ms). Luminescence of (Gd³⁺)* in ammonia is quenched by a solvated electron (e_s^–) formed during the dissolution of lithium metal. Under these conditions, the Gd³⁺ and e_s^– solution is unstable, precipitates are formed, and there is a continuous change in the concentrations of the components involved in the quenching reaction (Gd³⁺)* + e_s^– → Gd²⁺. Because of this, the gadolinium ion photoluminescence intensity this not applicable to assessing the quenching efficiency by a solvated electron. The quenching efficiency (τ₀–τ)/τ linear dependence the on the quencher concentration was obtained by measuring the gadolinium ion τ at a variable concentration e_s^–, which was determined from the solution optical density at 1400 nm in its absorption band. The bimolecular rate constant for the proposed quenching reaction, found from this dependence, was k = (5.3 ± 0.3) × 10⁷ M⁻¹ ∙ s⁻¹.