Influence of excitation light on the frequency upconversion of trivalent lanthanide ions

The upconversion mechanisms of the 1D2 level of Tm3+ ion under different excitation lights were analyzed. The influences of the excitation lights on the upconversion process, nonradiative relaxation from level 3F2 to 3H4 and fluorescence properties were investigated. It was shown that the one-color cw excitation could affect the profile of fluorescence, while information of the nonradiative relaxation could not be extracted. The nonradiative relaxation rate measured with the one-color pulsed excitation in crystal phase was in agreement with what was obtained in the free-standing nanometer crystal particles through the two-color pulsed excitation. The characteristics of the fluorescent emissions of Tm3+ ions doped in various host materials were also discussed under different excitation lights. As a result of the discussion, a possible way to obtain nonradiative relaxation rate directly from a spectroscopic method in frequency domain was proposed. The study can be extended to other trivalent lanthanide ions that have upconversion through excited state absorption.