Upconversion and energy transfer dynamics in Nd 3+:KLiYF 5

Abstract

A detailed study of the spectroscopy, mechanism and dynamics of orange and green luminescence that results from infrared pumping of Nd 3+:KLiYF 5 is presented. The transitions involved are determined using luminescence spectroscopy at 10 K. All orange and green luminescence emanates from the 4 G 7/2 and 4 G 5/2+ 4 G 7/2 states. The mechanism that populates upper emitting levels is determined through analysis of excitation spectra, excitation power dependence and luminescence lifetimes to be energy transfer between ions in the 4 F 3/2 metastable state. A rate-equation model determines the donor–acceptor pathways that dominate the energy transfer mechanism. Only two of four possible pathways operate, promoting acceptor ions to the 4 G 7/2 or 4 G 11/2+ 2 D 3/2+ 2 G 9/2+ 4 K 15/2 states while demoting donor ions to the 4 I 13/2 or 4 I 11/2 states respectively. These two pathways have substantially greater energy overlaps than the two possible routes that do not operate, strongly suggesting a Förster–Dexter transfer mechanism. The results are discussed in terms of their relevance to Nd 3+-doped laser gain media.