Upconversion luminescence of Yb3+/Ho3+/Er3+/Tm3+ co-doped KGd(WO4)2 powders

Different lanthanide ions (Yb3+/Ho3+/Er3+/Tm3+) codoped KGd(WO4)2 phosphors were prepared by high-temperature solid-state reaction. The upconversion luminescence properties of two-ion and three-ion co-doped KGd(WO4)2 phosphors were investigated in detail. The concentration quenching effect of the two-ion co-doped KGd(WO4)2 phosphors was studied, and the optimum concentration of Ho3+, Er3+ and Tm3+ are 2 mol.%, 2 mol.% and 3 mol.%, respectively. The Yb3+/Ho3+/Tm3+ co-doped KGd(WO4)2 sample is the best white upconversion luminescence material among three-ion co-doped KGd(WO4)2 phosphors. The CIE coordinates for the samples were calculated, and chromaticity coordinates were close to white light regions. The upconversion luminescence mechanism of the samples was discussed. The upconversion luminescence of Ho3+ and Er3+ was both produced through two-photon process. The emissions of Ho3+ at 546 and 654 nm originated from the transition of Ho3+ (5S2→5I8 and 5F5→5I8), while those of Er3+ at 530 and 551 nm were attributed to the transition of Er3+ (2I11/2→4I15/2 and 4S3/2→4I15/2). The upconversion luminescence mechanism of Tm3+ was a three-photon process. The blue emission of Tm3+ was due to the transition of Tm3+ (1G4→3H6).