Efficiently visible and 2 μm infrared emission in K2YbF5: Ce3+/Ho3+ microcrystals

Ho3+/Ce3+ co-doped K2YbF5 microcrystals were synthesized by solvent-thermal method. Under excitation of 980 nm laser diode, effectively visible and 2 μm-infrared luminescence of Ho3+ ion were obtained in the microcrystals. By changing Ce3+-ion doping concentration, the luminescence properties of visible and 2 μm emission were effectively regulated. At low Ce3+-ion doping level, the red and green upconversion emission obviously increases and decreases respectively with the increase of Ce3+-ion amount in the samples, meanwhile the intensity of 2 μm fluorescence changes very little. At high Ce3+-ion doping level, the intensities of the red and green emission both decrease with the increase of Ce3+-ion concentration, while the 2 μm emission intensity increases obviously. In the sample doped with 16% Ce3+ ion, the intensity of 2 μm emission is about 4.5 times that of the sample without Ce3+ ion, and the corresponding quantum efficiency is about 78.3%. The result is attributed to the influence of the different cross relaxation between Ho3+ and Ce3+ ion in luminescence process at low and high Ce3+-ion doping concentration. The corresponding luminescence mechanism and energy transfer process were discussed in detail.