The basic spectroscopic parameters of Ho3+-doped fluoroindate glass for emission at 3.9 μm

This report details the first study of the fundamental spectroscopic properties of a new optical material for prospective application as a gain medium for fiber laser emission at 3.9 mu m. We have investigated the decay processes that are relevant to the excited states of the I-5(5) -> I-5(6) transition in singly Ho3+-doped InF3 (fluoroindate) glass using time-resolved fluorescence spectroscopy. The HoF3 concentration in the glass was 10 mol.%. We excited the I-5(7) and I-5(6) energy levels using selective excitation at 1982 nm and 1150 nm, respectively. We have established that a strong energy-transfer upconversion process by way of the well-known dipole-dipole-interaction between two holmium ions excited to the I-5(6) level populate the I-5(5) (upper laser) level of the 3.9 mu m transition. The I-5(6) and I-5(5) energy levels emit luminescence with measured peaks located at 2.85 mu m and 3.92 mu m, respectively and the luminescence-efficiencies of these emissions are 78% and 0.2%, respectively. Results from numerical simulations show that for this high Ho3+ concentration, a population inversion for the 3.9 gm transition is reached only for a short time (t < 100 mu s) after direct upper laser level pumping at a wavelength of 889 nm. (C) 2016 Elsevier B.V. All rights reserved.