Upconversion in YAlO3:Er pumped at 800 nm

Fluorescence at 3 μm and 545 nm in a YAlO3:Er (30 at.%) crystal has been measured as a function of wavelength, intensity and polarization for the excitation in the 800 nm wavelength region. Emission at 545 nm is an indicator of losses for 3 μm emission due to excited-state absorption and upconversion. The experimental results allow to determine the excitation mechanisms, the upconversion coefficient W2 and the optimum pump wavelengths to generate 3 μm radiation.