Upconversion multicolor tuning of NaY(WO4)2:Tb3+ with Eu3+ doping

A series of Tb³⁺ and Eu³⁺ co-doped NaY(WO₄)₂ phosphors were synthesized by hydrothermal reactions. The crystal structure, morphology, upconversion luminescent properties, the energy transfer from Tb³⁺ to Eu³⁺ ions and the ⁵D₄ → ⁷F₅ transition of the Tb³⁺ ion in NaY(WO₄)₂:Tb³⁺,Eu³⁺ phosphors were investigated in details. The results indicate that all the synthesized samples are of pure tetragonal phase NaY(WO₄)₂. Furthermore, the micrometer-sized needle spheres and excellent dispersion of the particles are obtained by adding polyethylene glycol (PEG-2000) as the surfactant. Phosphors of NaY(WO₄)₂:Tb³⁺,Eu³⁺ exhibit the 492 nm blue emission peak, 546 nm green emission peak, 595 nm orange emission peak and 616 nm red emission peak under 790 nm excitation. The energy transfer from Tb³⁺ to Eu³⁺ is a resonant transfer, in which electric dipole–dipole interaction plays a leading role. By adjusting the doping concentration of Eu³⁺ in NaY(WO₄)₂:1.0 mol%Tb³⁺,xmol%Eu³⁺ phosphors, the emitting color of UC phosphors can be tuned from green to red.