ELECTRON-SPIN-RESONANCE AND MOSSBAUER STUDIES OF CAS-EU SYNTHESIZED USING THE FLUX METHOD

CaS:Eu phosphors were synthesized using the flux method. ESR and Mossb auer spectroscopies show the coexistence of Eu3+ and Eu2+. Eu3+ and Eu 2+ are mainly observed in phosphors obtained with Na2Sz ((Na) phosphor s) and K2SZ fluxes ((K) phosphors), respectively. The Eu2+ fraction in (K) phosphors varies with total Eu content and temperature of synthes is. Under reducing thermal treatment, part of the Eu3+ is converted in to Eu2+ in (Na) phosphors, and also in (K) phosphors with Eu content l ess-than-or-equal-to 10(-3) mole. For the latter phosphors, addition o f chloride ions in the flux enhances the Eu2+ level, and after reducin g thermal treatment practically all europium ions are in the Eu2+ stat e. In similar conditions, (K) phosphors with more than 10(-2) mole Eu exhibit nearly no Eu2+ level variation, and (Na) phosphors undergo a s eparation of phases to obtain CaS:Eu3+ and Cag:Eu3+Eu2+. Interpretatio n of the various features on the basis of Na (K), Eu codoping and dopa nt-induced lattice distortions is proposed. It is suggested that (K) p hosphors are partially oxygenated, with Eu3+ ion charge balanced by K ions and/or Ca2+ vacancies.