Energy transfer of the quantum-cutter couple Pr3+-Mn2+ in CaF2:Pr3+, Mn2+ nanoparticles

CaF2:Pr (1 mol%), CaF2:Mn (5 mol%) and CaF2:Pr,Mn (1 mol%, 5 mol%) nanoparticles are prepared via a microwave-mediated synthesis in ionic liquids. The nanoparticles are highly crystalline and exhibit particle diameters <50 nm.In contrast to bulk-CaF2:Pr,Mn,energy transfer between Pr3+and Mn2+under 1S0→1I6 relaxation on Pr3+ and 4G(4T1g)→6S(A1g) emission of Mn2+ is observed for the first time. Such energy transfer represents the essential first step of the quantum-cutting cascade via the Pr3+-Mn2+ couple, which is most interesting as both expected photons - 3P0→3H4 emission of Pr3+and 4G(4T1g)→6S(A1g) emission of Mn2+ - are emitted in the green spectral range. While bulk crystals were said not to show energy transfer due to prohibiting selection rules, vacuum ultraviolet (VUV) spectroscopy of CaF2:Pr, Mn nanoparticles firstly proves efficient Pr3+→Mn2+ energy transfer, which can be ascribed to the reduced site symmetry and considerable spin-orbit interaction in the nanocrystals.