Hydrothermal synthesis, multicolor tunable luminescence and energy transfer of Eu³⁺ or/and Tb³⁺ activated NaY(WO₄)₂ nanophosphors

Eu³⁺ and/or Tb³⁺ doped NaY(WO₄)₂ nanomaterials have been successfully synthesized by one-step hydrothermal method. The samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, X-ray energy dispersive spectroscopy, and photoluminescence spectra. The results show that the novel nanoplates with a diameter of 300–600 nm and the thickness of 20–25 nm are observed. Under the excitation of 246 or 230 nm, individual RE³⁺ ions activated NaY(WO₄)₂ phosphors exhibit excellent emission properties in their respective regions. The as-prepared Eu³⁺ or Tb³⁺ doped samples show strong red and green emission, originating from the allowed ⁵D₀ → ⁷F_J (J = 0, 1, 2) transition of the Eu³⁺ ions and the ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transition of the Tb³⁺ ions. In addition, by properly tuning the relative concentration of Eu³⁺ ions in the case of Eu³⁺ and Tb³⁺ co-doped systems, tunable emissions in a single component are obtained under the excitation of 230 or 395 nm. Moreover, an energy transfer from Tb³⁺ to Eu³⁺ is observed, which has been justified through the luminescence spectra and the fluorescence decay curves. Furthermore, the corresponding luminescence and energy transfer mechanism have been proposed in optical transitions and possible energy transfer scheme. These results indicate that Eu³⁺ and Tb³⁺ doped NaY(WO₄)₂ phosphors will find potential application in the field of solid-state lighting.