Tunable red-green-blue multicolor luminescence in Yb3+/Tm3+/Ho3+:Gd3Ga5O12 nano-crystals

► We prepared Yb3+/Tm3+/Ho3+: Gd3Ga5O12 nano-crystals via a sol-gel process. ► Red-green-blue up-conversion luminescence and mechanisms are investigated. ► The emission color of the phosphors is tunable by adjusting the doping concentrations of Yb3+/Tm3+/Ho3+ and laser pump power. The Yb3+/Tm3+/Ho3+: Gd3Ga5O12 nano-crystals have been successfully prepared via a citric acid complex procedure. The luminescence spectra were measured and the up-conversion processes were discussed. By means of adjusting the doping concentrations of Yb3+/Tm3+/Ho3+, the red-green-blue up-conversion luminescence changed obviously. Results indicated that the ratio of red-green-blue up-conversion emissions enhanced heavily with the increasing concentrations of Tm3+ doped in the Yb3+/Tm3+/Ho3+:Gd3Ga5O12 nano-crystals, which was rooted in the three-photon resonant cross relaxation processes(1G4 (Tm)+5I7 (Ho)→3H5 (Tm)+5S2 (Ho)). The tunable red-green-blue luminescence could be used in the fields of display, illumination, and photonics such as the white light generation.