Christine Reinhard, Pascal Gerner, Fernando Rodríguez, Sara García-Revilla, Rafael Valiente and Hans U. Güdel
Near-infrared to green photon upconversion in Mn²⁺ and Yb³⁺ doped lattices
Chem. Phys. Lett. 386, 132-136 (2004)                 

Abstract: Yb³⁺ excitation in the near-infrared around 1 mm leads to green Mn^{2+ 4}T₁   ⁶A₁ luminescence in CaZnF₄:Mn²⁺; Yb³⁺, Zn₂SiO₄:Mn²⁺; Yb³⁺ and SrZnCl₄:Mn²⁺; Yb³⁺ at 15 K. In the former two compounds the green upconversion (UC) luminescence is visible by eye up to room temperature. In Cs₃MnBr₅:Mn²⁺; Yb³⁺ no UC luminescence is observed. The UC mechanism consists of a sequence of ground-state absorption and excited-state absorption steps. The UC efficiency at 15 K is of the order of 1% for laser excitation with 130 mW (f=53 mm focusing lens).