Blue and white upconversion emissions of rare-earth ions-doped oxyfluoride phosphors

A blue emitting upconversion phosphor based on Yb3+ and Tm3+ codoped oxyfluoride is reported. Under the excitation of a single 980 nm diode laser with the power density of 5.56 W/cm2, the upconversion luminescence brightness can reaches to 13053 mcd/m2, which is much stronger than that of commercial Y2O2S:Yb, Tm phosphors (8194 mcd/m2). The research of upconversion mechanism indicates that cooperating sensitization dominates the emissions at 479 and 645 nm, while the emission at 454 nm results from the combination of cooperating sensitization and phonon-assisted energy transfer from Yb3+ to Tm3+. Also, bright upconversion white light is obtained by tri-doping of Er3+, Tm3+ and Yb3+. Because the blue (main emission at 479 nm), green and red emissions are two-photon process, the white light is not sensitive to the pumping power.