Anomalous up-conversion dynamics in rare-earth doped yttrium oxide powders

We performed up-conversion (UC) experiments in rare-earth (Er3+, Tm3+, Nd3+) doped yttrium oxide (Y2O3) powders using a high power (1.6 W) near-infrared (808 nm) diode laser modulated at 20 Hz as the excitation source. Below the threshold for incandescence, the analysis of the dynamics of the UC luminescence showed the presence of an unusual depletion of the luminescence signal. This anomalous effect could be controlled by the laser excitation power or the modulation frequency or the combination of rare-earth species doped in the samples. The phenomenon was associated with a thermo-optical effect generated by strong laser absorption, poor thermal dissipation of the powder and energy transfer (ET) between different rare-earth species. The experimental results also led us to believe that the ET mechanism cools down the rare-earth donor, Tm3+, and heats up the rare-earth acceptor, Er3+.