LUMINESCENCE AND ENERGY-TRANSFER IN CAF2 SLIGHTLY DOPED WITH EUROPIUM AND MANGANESE

The optical properties (emission, excitation and lifetime data) of CaF 2 slightly contaminated with Eu2+ and Mn2+ ions have been analysed in the present investigation. The optical properties of the systems CaF2:Eu2+ and CaF2:Mn2+ have also been studied in order to obtain a better characterisation of the optical properties of the CaF2:Eu:Mn phosphor material. The spectroscopic data obtained clearly indicate that energy transfer from the donor Eu 2+ ions to the acceptor Mn2+ ions takes place in CaF 2 even at the very low impurity concentrations employed in the authors' samples, suggesting therefore that the impurities are not randomly distributed in the lattice but rather occur as impurity clusters of Eu 2+ to Mn2+. Some insight into the possible nature of the impurity complexes as well as of the Eu to Mn energy transfer mechanism taking place inside them were gathered with the help of Dexter's theory for energy transfer phenomena. The results presented in this paper give support to the ionic radius criterion proposed by Rubio et al. (1985-9) to predict impurity pairing in a solid material.