Ba₂Ln_2/3TeO₆ (Ln = La, Pr, Nd, Sm, and Eu) double perovskites were synthesized via solid-state ceramic route. Preliminary X-ray diffraction studies indicated a pseudocubic structure with lattice parameters ranging from 8.55 to 8.44 Å for the substitution of rare earths from La to Eu. Raman spectra show the frequency dependence of various Raman bands with respect to rare-earth substitution and exhibit a significant shift in peaks to higher wavenumber region, which was observed only for symmetric stretching modes of LnO₆ and TeO₆ octahedra. In accordance with observed number of bands and group theoretical predictions, the most likely symmetry of all compounds in the Ba₂Ln_2/3TeO₆ system was found to be monoclinic with P2₁/n space group. Rietveld refinement of the XRD patterns further confirmed the P2₁/n space group and also the 1:1 rock salt ordering of the B-site cations. Diffuse reflectance spectra of Ba₂Ln_2/3TeO₆ showed the optical bandgaps of these compounds between 3.9 and 4.8 eV, indicating the suitability as luminescent host material. The reduction in bandgap energy with lanthanide contraction of rare-earth ions is attributed to the widening of conduction band with octahedral tilting. Photoluminescence (PL) spectra and PL excitation spectra of Ba₂La_2/3–xEu_xTeO₆ (x = 0.025, 0.05, 0.075, 0.1, 0.125, 0.15) were investigated and found to exhibit bright orange-red emission under UV excitation. Chromaticity coordinates closely resemble those of commercial red phosphor Sr₂Si₅N₈:Eu²⁺, which points toward the possible applicability of these new red phosphors in solid-state lighting industry. Finally, Judd–Ofelt intensity parameters Ω_λ (λ = 2 and 4) were calculated, which indicate that Eu³⁺ ions occupy the symmetric octahedral B-site of the Ba₂La_2/3TeO₆.

中文翻译：

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B站点有序Ba ₂ Ln _2/3 TeO ₆（Ln = La，Pr，Nd，Sm和Eu）双钙钛矿的结构表征及其作为Eu ³⁺荧光体的发光

通过固态陶瓷路线合成了Ba ₂ Ln _2/3 TeO ₆（Ln = La，Pr，Nd，Sm和Eu）双钙钛矿。初步的X射线衍射研究表明，伪立方结构的晶格参数范围为8.55至8.44Å，用于从La到Eu替代稀土。拉曼光谱显示了各种拉曼谱带相对于稀土取代的频率依赖性，并且显示出峰向较高波数区域的显着偏移，这仅在LnO ₆和TeO ₆八面体的对称拉伸模式下才能观察到。根据观察到的谱带数目和组理论预测，Ba ₂ Ln中所有化合物的最可能对称性发现_2/3 TeO ₆系统是单斜的，具有P 2 ₁ / n空间群。XRD图案的Rietveld精修进一步证实了P 2 ₁ / n空间群以及B位阳离子的1：1岩盐有序性。Ba ₂ Ln _2/3 TeO _6的漫反射光谱显示这些化合物的光学带隙介于3.9和4.8 eV之间，表明它适合用作发光基质材料。稀土离子的镧系元素收缩带隙能的降低归因于八面体倾斜导致的导带变宽。Ba的光致发光（PL）光谱和PL激发光谱_研究了2 La _{2 / 3- x} Eu _x TeO ₆（x = 0.025，0.05，0.075，0.1，0.125，0.15），发现在UV激发下显示亮橘红色。色度坐标与市售红色荧光粉Sr ₂ Si ₅ N ₈：Eu ²⁺极为相似，这表明这些新型红色荧光粉在固态照明行业中的适用性。最后，贾德-Ofelt理论强度参数Ω _λ（λ= 2和4）分别计算，这表明，将Eu ³⁺离子占据的Ba中的八面体对称B位₂的La _2/3的TeO₆。