Bright white up-conversion emission from Yb3+/Tm3+/Ho3+ tri-doped M-AgGd(WO4)2 phosphors

Monoclinic Yb3+/Tm3+/Ho3+ tri-doped AgGd(WO4)2 phosphors were prepared by the high temperature solid-state method. White emission via up-conversion process consisting of the blue UC radiations at 475 nm corresponding to the 1G4→3H6 transitions of Tm3+ ion, green at 542 nm to the 5F4, 5S2→5I8 transition of Ho3+ ions and red at 650 nm including both the 5F5→5I8 transition of the Ho3+ ion and the 1G4→3F4 transition of Tm3+ ion, was observed in the as-prepared powders under the excitation of a 980 nm diode laser. On the basis of spectral and pump power dependence analyses, the blue emission originated from the three-photon process and the green and red emissions originated from the two-photon process, the UC mechanisms for the fine-tuned white output were discussed in detail. Bright white luminescence upon 980 nm near-infrared excitation can be observed for the sample at the optimum chemical composition of AgGd0.737Yb0.200Ho0.013Tm0.05(WO4)2, which is produced via an up-conversion (UC) process by tuning the dopant ions Tm3+ concentration. By doping of Mo6+, the structure and UC properties of the Yb3+/Tm3+/Ho3+ tri-doped monoclinic AgGdW2O8 transformed to a tetragonal one, and the color of UC emission were also tuned with the increase of Mo6+ concentration. Bright white luminescence upon 980 nm near-infrared excitation can be observed for the sample at the optimum chemical composition of AgGd0.737Yb0.200Ho0.013Tm0.05(W0.6Mo0.4O4)2, which is about 9.5 times to that of the AgGd0.737Yb0.200Ho0.013Tm0.050(WO4)2.