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 S-1(0)-> I-1(16) relaxation on Pr3+ and (4)G(T-4(1g))-> S-6(A(1g)) 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 - P-3(0) -> H-3(4) emission of Pr3+ and (4)G(T-4(1g))-> S-6 ((A1)g) 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. (C) 2016 Elsevier B.V. All rights reserved.