Pure red upconversion emission from CaF2:Yb3+/Eu3+

Single phase cubic CaF2 microcrystals co-doped with Eu3+ and Yb3+ ions were synthesized through a coprecipitation process followed by annealing at 1200°C. Under the excitation of 980nm laser, the intensive emission at ~614nm (5D0 → 7F2) in the red region was observed at room temperature. The color coordinate of CaF2:0.1%Yb3+/0.1%Eu3+ was calculated with the Commission Internationale de I’Eclairage (CIE) chromaticity coordinate of (x=0.572, y=0.265). The excitation of Eu3+ ions came from the energy transfer of Yb3+-dimers through a cooperation sensitization process. Furthermore, not only the emissions from the 5Di (i=0, 1, 2, 3)→7Fj (j=0, 1, 2, 3) transitions but also the rarely reported emission (~398nm) from the 5L6 →7F0 transition was recorded. The cooperation sensitization process was so effective in the Yb3+/Eu3+ co-doped system that all the cooperative luminescence (CL) from Yb3+-clusters were quenched and only the red upconversion luminescence of Eu3+ ions could be seen.