Upconversion excitation of Cr3+ emission in YAlO3 codoped with Cr3+ and Yb3+

We report on upconversion (UC) luminescence in YAlO3 codoped with 0.3% Cr3+ and 6% Yb3+. At 10 K excitation around 10,400 cm−1 leads to red Cr3+ pair luminescence at 14,000 cm−1. The UC excitation spectrum of the red Cr3+ luminescence is very similar to the squared Yb3+ absorption spectrum. This demonstrates that two Yb3+ 2F7/2→2F5/2 excitations are involved in the UC process. From transient measurements, the UC mechanism is found to be dominated by an energy transfer step: Two excited Yb3+ ions simultaneously transfer their excitation energy to a nearby Cr3+ pair.