Synthesis and spectral analysis of Yb3+/Tm3+/Ho3+-doped Na0.5Gd0.5WO4 phosphor to achieve white upconversion luminescence

Yb3+/Tm3+/Ho3+-doped Na0.5Gd0.5WO4 phosphors were synthesized by the high-temperature solid-state method. Bright white luminescence upon 980 nm near-infrared excitation can be observed for the sample at the optimum chemical composition of Na0.5Gd0.5WO4:10%Yb3+/1%Tm3+/0.4%Ho3+, which is produced via an upconversion (UC) process by tuning the dopant ions concentration. The measured white light consists of the blue, green, and red UC emissions which correspond to the transitions 1G4 → 3H6 of Tm3+, 5F4(5S2) → 5I8, and 5F5 → 5I8 of Ho3+ ions, respectively. The calculated color coordinates display that white light can be achieved in a wide range of dopant concentrations. The UC mechanisms were also proposed based on their spectral and pumping power dependence analyses.