ELECTRONIC-STRUCTURE OF PR3+ AND TM3+ DOPED LIYO2

An optical investigation of LiYO2 doped with 2% Pr3+ and 5% Tm3+ is pr esented. The unit cell is monoclinic and the site symmetry at the rare earth site is C-1. The absorption, excitation and fluorescence spectr a at 20 K are utilized to determine the electronic structure of the gr ound 4f(2) and 4f(12) configurations respectively. For LiYO2:Pr3+ 64 e nergy levels from H-3(4) up to P-3(2) at 22 000 cm(-1) are reported. F or LiYO2Tm-1, 58 energy levels from H-3(6) up to P-3(2) at 38 000 cm(- 1) and the relative intensities for absorption from the H-3(6) ground state are given. A crystal field analysis of the data is performed. Co nfiguration interaction is applied to LiYO2:Pr3+ and improves the resu lts. While Eu3+ and Tb3+ doped LIYO2 are good red and green phosphors respectively, LiYO2:5%Tm3+ luminesces only weakly. The reason for that is the existence of many possible paths for up-conversion processes. (C) 1998 Elsevier Science S.A.