SPECTROSCOPY AND DYNAMICS OF UPCONVERSION IN TM-3+-YLIF4

Spectroscopic and dynamic properties of Tm3+:YLiF4 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 1S0 of Tm3+. The observed energy levels were fitted in a least-square analysis to determine crystal-field parameters of the S4 site of Tm3+ in YLiF4 with a standard deviation of 16 cm-1 between the calculated and measured energy levels. Judd-Ofelt calculations using measured integrated absorption yield the intensity parameters OMEGA-2,4,6 for Tm3+ in YLiF4. From these parameters, the calculated stimulated emission cross section of the 1D2 --> 3F4 transition is 2.4 x 10(-19) cm2, in good agreement with the measured value of 3 x 10(-19) cm2. 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.