Energy transfer and multicolor emission in single-phase Na5Ln(WO4)4−z(MoO4)z:Tb3+,Eu3+ (Ln = La, Y, Gd) phosphors

Abstract

A series of Tb³⁺ and/or Eu³⁺-doped Na₅Ln(WO₄)_4−z(MoO₄)_z (0 ≤ z ≤ 4, Ln = La, Y, Gd) phosphors have been prepared via a simple Pechini method. X-ray diffraction (XRD) profile analyses have verified the formation of a single phase with scheelite-like structure. The scheelite-like tetragonal structure provides the Na₅Ln(WO₄)₄ hosts the possibility of doping with Tb³⁺/Eu³⁺ ions without substantial luminescence quenching. Under near UV light excitation, Tb³⁺ and Eu³⁺-doped Na₅Ln(WO₄)₄ phosphors exhibit characteristic emissions of Tb³⁺ (⁵D_3,4 → ⁷F_J) and Eu³⁺ (⁵D₀ → ⁷F_J), respectively. By codoping the Tb³⁺ and Eu³⁺ ions into the Na₅Ln(WO₄)₄ host and tuning their relative concentration ratio, multicolor tunable emissions are obtained by varying the ratio of Tb³⁺/Eu³⁺. The energy transfer from Tb³⁺ to Eu³⁺ in Na₅Ln(WO₄)₄ has been investigated by photoluminescence and decay measurements. The influence of W substitution by Mo on the luminescence properties of Na₅Ln(WO₄)_4−z(MoO₄)_z:Tb³⁺/Eu³⁺ has also been investigated. Both the emission intensities of Tb³⁺ and Eu³⁺ ions were found to reach a maximum when the molar ratio of W/Mo was 2 : 2. The results suggest that Na₅Ln(WO₄)_4−z(MoO₄)_z:Tb³⁺/Eu³⁺ phosphors might find potential applications in the field of solid state lighting and field emission displays.