配位体 SO_4~(2-)对激发态铀(Ⅵ)去活化的影响

近年来,随着激光、微弱信号测量以及瞬态测量技术等发展,对溶液中激发态离子的化学和物理行为的研究已日益受到人们的重视,激发态铀酰离子发光衰减的研究尤为活跃.Marcantonatos 等、Formosinho 等以及郑企克、王志麟等对高氯酸溶液中激发态铀酰离子的发光衰减过程进行了详细的研究.探讨了ClO_4~-溶液中pH 等对激发态铀酰离子的发光衰减的影响,观察到了一定的pH 条件下激发态铀(Ⅵ)的非单一指数衰减,并各自提出了不同的解释.值得提出的是,上述的一系列研究都是在高氯酸溶液中,其它体系中铀(Ⅵ)的发光哀减的研究进行得很少,报导则更少.1983年Joshi 等曾研究了80K 时SO_4~(2-)

THE EFFECTS OF COMPLEX FORMATION ON THE DEACTIVATION OF ELECTRONICALLY EXCITED URANYL IONS

The dependence of the luminescence decay of electronically excited uranyl ionson the concentrations of uranium and sulphate in aqueous solution has been investiga-ted with a pulsed nitrogen laser as a light source and a programmable transient re-corder for lifetime measurements.Single exponential decay of the Luminescence is ob-served.The deactivation process of the excited uranyl ions should include radiative,nonradiative,water quenching and uranium self quenching and the measured lumine- scenec lifetime indicates the result of all these processes.The Luminescence lifetimeof uranyl ions increases with increasing concentration of sulphate and becomes constantwhen the equilibrium concentration of sulphate reaches 3.0mol.L~(-1).The dependenceof the Luminesence lifetime is similar to that of the UO_2(SO_4)_3~(4-) formation.This phenomenon can be interpreted in terms of the fact that in aqueous solutionuranylions exist as aquo-uranylions.As the concentration of sulphate increaes thewater molecule of hydrated uranyl ions will be replaced by sulphate ions via complexformation,and the quenching of excited uranylions by water is reduced.The selfquenccing and the water quenching rate constants of UO_2(H_2O)_6~(2+) and UO_2(SO_4)_3~(4-)are estimated.Based on the experimental results a model for the deactivation mecha-nism of excited uranyl ions in sulphate solution is proposed.