Pure and RE3+-Doped La7O6(VO4)3 (RE = Eu, Sm): Polymorphism Stability and Luminescence Properties of a New Oxyvanadate Matrix

(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-x(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-x(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 (J = 5, 4, 3). Hence, the Tb³⁺-doped Na₃La(VO₄)₂ phosphors have potential applications for white-light-emitting diodes.

High pressure exploration in the Li-Ln-V-O system

Using in situ high pressure Raman spectroscopy, two structural changes were observed in a sample of the composition LiLa5O5(VO4)2. Taking this into account and by combining different conditions, three new compounds were further obtained from high pressure-high temperature synthesis. Their crystal structure description was done using the antiphase approach, which implies the presence of oxygen-centered [OLn4] building units, where Ln is La for (1) β-LiLa5O5(VO4)2 and (2) β-LiLa2O2(VO4) or Nd for (3) LiNd5O5(VO4)2 compounds. (1) crystallizes in the triclinic space group P1[combining macron] with unit cell parameters of a = 5.8167(15) Å, b = 12.2954(28) Å, c = 18.7221(69) Å, α = 102.03(2)°, β = 98.76(2)°, and γ = 103.54(2)°; a 3D structure was deduced from the ambient pressure polymorph. (2) also crystallizes in P1[combining macron] with a = 5.8144(7) Å, b = 5.8167(7) Å, c = 8.5272(1) Å, α = 98.184(7)°, β = 100.662(7)° and γ = 92.579(7)°. It shows a 2D structure with [La2O2]2+ layers surrounded by [LiO4] and [VO4] tetrahedra sharing corners and edges. (3) exhibits a 3D architecture isotypic with AP-LiLa5O5(VO4)2. The crucial role of high pressure in such types of synthesis and materials is also discussed.

Ultra-high sensitivity of multicolor Sm3+-doped LiSrVO4 phosphors for contactless optical thermometers

Multicolor Sm³⁺-doped LiSrVO₄ phosphors with ultra-high S_a and S_r values of 1.076 K⁻¹ and 6.167% K⁻¹, respectively, are promising candidates for contactless thermometers.