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.