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.