Visible-to-near-IR luminescence at stepwise up-conversion in Yb,Ho:GGG under IR diode pumping

Powerful visible-to-near-IR luminescence is observed in a Gadolinium Gallium Garnet crystal co-activated with Yb3+ (∼15 at%) and Ho3+(∼0.1 at%) at CW laser diode excitation (λ=938 nm). The main visible emission band is observed in the green with its peak at λ∼540 nm and measured to be about 8–10% with respect to Yb3+ IR luminescence (λ∼1000 nm). Red (λ∼650 nm) and near-IR (λ∼755 nm) emission bands are also observed but are weaker (about 3–5%). Analysis of the crystal absorption and luminescence spectra allows one to conclude that Yb3+–Ho3+ stepwise up-conversion is the mechanism explaining the phenomenon.