Synthesis and luminescence studies of CaF^sub 2^:Yb:Pr solid solutions powders for photonics

Praseodymium- and ytterbium-doped calcium fluoride powder samples were prepared by co-precipitation from aqueous solutions followed by annealing at 600 °C. Phase and microstructure analyses of these fluorite-type solid solution samples were carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM), which have demonstrated the average particle size to be about 30 nm, ∼100 nm after drying at 45 °C and annealing at 600 °C, respectively. The fluorescence studies under 443 nm excitation in 3H4 – 3P2 band of Pr3+ ions allowed us to determine the optimal chemical compositions of CaF2:Yb:Pr samples with the high Pr3+->Yb3+ energy transfer efficiency exceeding 90% and down-conversion luminescence efficiency up to 50%. The optimal compositions are: Yb:Pr = 10.0:0.05; 10.0:0.1; and 5.0:0.05 mol%. This confirms that the energy transfer from praseodymium to ytterbium occurred via quantum cutting mechanism, and the optimal composition for highly efficient phosphor application appears to be CaF2:Yb(10.0 mol%):Pr(0.1 mol%).