(3+1)-Dimensional Modulated Structure and Tb³⁺-Doped Luminescence for Vanadate Na₃La(VO₄)₂

A modulated structure with symmetrical characteristic higher than three-dimensional is a fascinating crystallographic type, and it is randomly encountered by researchers. Herein, we prepared 0.1 mm level single crystals of Na₃La(VO₄)₂ and determined its structure to be a (3 + 1)-dimensional modulated structure using the X-ray diffraction analysis method for single crystals. Its super space group was determined to be Pca2₁(0β0)000. On the other hand, we introduced Tb³⁺ into the Na₃La(VO₄)₂ host lattice to fabricate phosphors Na₃La_1-(VO₄)₂:xTb³⁺ and studied their photoluminescence properties. Interestingly, for the strong absorption of the Na₃La(VO₄)₂ host lattice in the range of 200-400 nm, the traditional 330-385 nm light is unable to efficiently excite Tb³⁺ ions in the Na₃La(VO₄)₂ host to generate luminescence of Tb³⁺. Instead, Na₃La_1-(VO₄)₂:xTb³⁺ is suitable to be excited by 487 nm to generate emitting light at 543, 584, and 622 nm, due to Tb³⁺ characteristic 4f → 4f transitions of ⁵D₄ → ⁷F (J = 5, 4, 3). Hence, the Tb³⁺-doped Na₃La(VO₄)₂ phosphors have potential applications for white-light-emitting diodes.