Luminescence study of the 4fsup(2)5d configuration of Ndsup(3+) in LiYFsub(4), LiLuFsub(4) and BaYsub(2)Fsub(8) crystals

Abstract

Ultraviolet fluorescence of Nd3+ ions induced by triphotonic excitation process was studied in Nd-doped LiYF4, LiLuF4 and BaY2F8 crystals using a technique of time-resolved spectroscopy. The observed ultraviolet luminescence was due to transitions between the bottom of 4f 2 5d configuration and 4f 3 states of Nd3+ ions. Narrow emission lines superposed to the broadband emissions were observed. A detailed analysis of luminescence spectrum revealed that the narrow emissions are due to parity and spin allowed radiative transitions from the Stark levels of 4 K11/2(5d) state created by the electrostatic interaction between the 5d electron and the two electrons of the 4f 2 configuration. The narrow emissions are related to the high spin state (S ¼ 3=2) which gives f–f characteristics to the f–d broadband emissions. The narrow emissions superposed to the wide emission correspond to 18%, 34% and 43% of the integrated broadband emission at 262 nm observed in LiYF4, LiLuF4 and BaY2F8 crystals, respectively. Although the 5d–4f 2 interaction is observed to be weaker than 5d-crystal field interaction, it is stronger enough to select only the radiative transitions from 4f 2 5d configuration to 4f 3 states that preserves the total spin S ¼ 3=2.