Upconversion and energy transfer dynamics in Nd3+: LiYF5

A detailed study of the spectroscopy, mechanism and dynamics of orange and green luminescence that results from infrared pumping of Nd3+:KLiYF5 is pre sented. The transitions involved are determined using luminescence spectros copy 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 emitt ing levels is determined through analysis of excitation spectra, excitation power dependence and luminescence lifetimes to be energy transfer between ions in the F-4(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) + D-2(3/2) + (2)G(9/2) + K-4(15/2) states while demoting donor ions to the I-4(13/2) or I-4(11/2) states respectively. These two pa thways have substantially greater energy overlaps than the two possible rou tes that do not operate, strongly suggesting a Forster-Dexter transfer mech anism. The results are discussed in terms of their relevance to Nd3+-doped laser gain media. (C) 2001 Elsevier Science B.V. All rights reserved.