Tunable upconversion emission in Ba2YF7:Yb3+/Er3+ nanocrystals with different Yb3+ concentration

Ba2YF7:xYb3+,0.02Er3+ nanocrystals with different Yb3+ concentration (x = 0.2, 0.4, 0.6, 0.8, 0.98) were synthesized via a solvothermal method. Their X-ray diffraction patterns reveal that all the samples are cubic phase without phase change at arbitrary Yb3+ concentration. Upon excitation of 980 nm laser, these nanocrystals display upconversion emission in the green and red spectral regions. The relative emission intensity at these two regions can be tuned by Yb3+ concentration. To investigate the effect of Yb3+ ion, the decay times of 650 nm emission were measured and analyzed. Ba2YF7:0.6Yb3+,0.02Er3+ nanocrystals have the longest lifetime and highest emission intensity among all the samples. We concluded the lifetime of 4F9/2 level has an effect on its own population and intensity ratio of red and green emission. Our results show Yb3+ ion can tune the upconversion emission and improve upconverison emission intensity.