RADIATION-INDUCED STABILIZATION OF UNUSUAL OXIDATION-STATES IN TL(I)LN(III) (SO4)(2)CENTER-DOT-4H(2)O (LN=SM, EU AND ND) - EPR INVESTIGATIONS

Double sulfates of thallium and lanthanides form an interesting series of compounds with first fractional crystallization leading to the for mation of tetrahydrated double sulfates. The radiation induced defects including changes in the oxidation states were studied by carrying ou t EPR investigations of gamma-irradiated Tl(I)Ln(III) (SO4)(2) . 4H(2) O (Ln = Sm, Eu and Nd) compounds. The important finding of these inves tigations is the formation of a radiation-induced paramagnetic center Tl2+ simultaneously with that of Eu2+, revealing their intrinsic assoc iation. Similar formation of Tl2+ was not observed in other rare earth salts, implying that the stability of the half-filled electronic conf iguration of Eu2+ may be responsible for the stabilization of Tl2+. Th eir relaxation back to Eu3+ and Tl+ simultaneously at 255 K gives furt her confirmation of their association and suggests that the matrix int rinsically does not favor the stabilization of Eu2+ as reported in a n umber of other matrices. The hyperfine coupling constant for Tl2+ was calculated using the Breit-Rabi equation and was found to be 80 GHz.