Radiation induced stabilization of unusual oxidation states in Tl (I) Ln (III) (SO₄)₂.4H₂O (Ln=Sm, Eu and Nd): EPR investigations

Abstract

Double sulfates of thallium and lanthanides form an interesting series of compounds with first fractional crystallization leading to the formation of tetrahydrated double sulfates. The radiation induced defects including changes in the oxidation states were studied by carrying out EPR investigations of γ-irradiated Tl (I) Ln (III) (SO₄)₂.4H₂O (Ln=Sm, Eu and Nd) compounds. The important finding of these investigations is the formation of a radiation-induced paramagnetic center Tl²⁺ simultaneously with that of Eu²⁺, revealing their intrinsic association. Similar formation of Tl²⁺ was not observed in other rare earth salts, implying that the stability of the half-filled electronic configuration of Eu²⁺ may be responsible for the stabilization of Tl²⁺. Their relaxation back to Eu³⁺ and Tl⁺ simultaneously at 255 K gives further confirmation of their association and suggests that the matrix intrinsically does not favor the stabilization of Eu²⁺ as reported in a number of other matrices. The hyperfine coupling constant for Tl²⁺ was calculated using the Breit-Rabi equation and was found to be 80 GHz.