Spectroscopy and dynamics of upconversion in Tm 3+: YLiF 4

Abstract

Spectroscopic and dynamic properties of Tm 3+: YLiF 4 as an upconversion material with blue emission are presented. Absorption, fluorescence and excitation spectra at low temperatures were used to determine the crystal field levels of all manifolds except 1S 0 of Tm 3+. The observed energy levels were fitted in a least-square analysis to determine crystal-field parameters of the S 4 site of Tm 3+ in YLiF 4 with a standard deviation of 16 cm −1 between the calculated and measured energy levels. Judd-Ofelt calculations usuing measured integrated absorption yield the intensity parameters μ 2,4,6 for Tm 3+ in YLiF 4. From these parameters, the calculated stimulated emission cross section of the 1D 2→ 3F 4 transition is 2.4 × 10 −19 cm 2, in good agreement with the measured value of 3 × 10 −19 cm 2. An estimate of the dipole-dipole interaction which gives rise to quenching of the excited state was derived from the fluorescence decay curves at different concentrations.