Enhanced red emission induced by Tb³⁺ doping in europium-based molybdate phosphors

Graphical abstract: The introduction of Tb3+ significantly enhances the red emission of Eu3+ in europium-based molybdate phosphors. The enhanced red emission intensity is discussed by the relaxation of parity-forbidden selection rules of Eu3+ ions, whereas the contribution of Tb3+ → Eu3+ energy transfer is little in our case. - Highlights: • The introduction of Tb³⁺ significantly enhances the red emission of Eu³⁺ in europium-based molybdate phosphors. • At x = 0.02, the red-emitting intensity of LiEuMo₂O₈ is enhanced by 30% under excitation at ultraviolet light 395 nm. • The enhanced red emission intensity is discussed by the relaxation of parity-forbidden selection rules of Eu³⁺ ions, whereas the contribution of Tb³⁺ → Eu³⁺ energy transfer is little in our case. - Abstract: A series of Tb³⁺-doped europium-based molybdate red-emitting phosphors (LiEuMo₂O₈) were prepared by solid-state reaction method, their crystal structure and luminescence properties have been investigated by X-ray diffraction, micro-Raman spectra, diffuse reflectance spectra, photoluminescence and photoluminescence excitation spectra. Partial substitution of Li⁺ by Tb³⁺ slightly distorts the host lattice, red-shifts the absorption edge of host and improves Eu³⁺ red-emitting intensity in LiEuMo₂O₈ compound. The red-emitting intensity of LiEuMo₂O₈ powder is enhanced by 30% at the doping level of 0.02 under excitation at 395 nm. In present study, we found that the contribution of Tb³⁺ → Eu³⁺ energy transfer to the enhanced Eu³⁺ emission is little since the Tb³⁺ ions are not responsive to the near ultraviolet (∼395 nm), the enhanced red emission is tentatively ascribed to the relaxation of parity-forbidden selection rules of Eu³⁺ ions. White light-emitting diodes are fabricated by using near ultraviolet light-emitting diode chips (∼395 nm) and the blends of the commercial blue, green and as-prepared red Li_0.98Tb_0.02EuMo₂O₈ phosphor, the resulting white light-emitting diode shows a color-rendering index of 93.5, luminous efficacy of 14 lm/W and chromaticity coordinates of (0.292, 0.329).