Emissive double molybdates, AEu(MoO₄)₂ (A = Na, K, Rb, Cs), have garnered significant attention due to the diversity of crystal structures depending on the ionic radius of A⁺ ions. However, the relationship between particle morphology and photoluminescence properties has not been reported for them. In this study, single-crystalline double molybdates were successfully synthesized by varying the molar ratio of A/Eu through a one-pot hydrothermal route without an annealing process. This approach allowed for the creation of a variety of crystal structures and particle morphologies. The two-dimensional (2D) layered materials of KEu(MoO₄)₂, RbEu(MoO₄)₂, and CsEu(MoO₄)₂ exhibit a luminescence intensity stronger than that of the scheelite-type NaEu(MoO₄)₂ with a three-dimensional (3D) framework structure because the layered structure can activate a higher concentration of Eu³⁺ ions due to the suppression of migration of excitation energy between Eu³⁺ ions. By varying the amount of A sources added, the morphologies were drastically changed, and their luminescence intensity was improved. Particularly, the particle morphologies of RbEu(MoO₄)₂ changed from rhombic nanoplate-like to rod-like and, finally, to hexagonal plate-like particles. The luminescence intensity achieved up to 5.8 times higher, attributed to the crystal growth along the in-plane direction of RbEu(MoO₄)₂ including the [EuO₈] layer.

中文翻译：

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通过一锅水热合成获得发射性单晶 AEu(MoO4)2（A = Na、K、Rb 和 Cs）双钼酸盐：颗粒形貌与光致发光性能之间的关系

发射性双钼酸盐，A Eu(MoO ₄ ) ₂ ( A = Na, K, Rb, Cs)，由于晶体结构的多样性（取决于A ⁺离子的离子半径）而引起了人们的广泛关注。然而，颗粒形态与光致发光性质之间的关系尚未见报道。在本研究中，通过一锅水热路线改变A /Eu的摩尔比，无需退火过程，成功合成了单晶双钼酸盐。这种方法可以创建各种晶体结构和颗粒形态。 KEu(MoO ₄ ) ₂、RbEu(MoO ₄ ) ₂和CsEu(MoO ₄ ) ₂的二维(2D)层状材料表现出比白钨矿型NaEu(MoO ₄ ) ₂更强的发光强度三维(3D)框架结构是因为层状结构由于抑制了Eu ^{3+离子之间的激发能的迁移而可以激活更高浓度的Eu 3+}离子。通过改变A源的添加量，形态发生了巨大的变化，并且其发光强度也得到了提高。特别是，RbEu(MoO ₄ ) ₂的颗粒形貌从菱形纳米板状变为棒状，最后变为六角板状颗粒。由于晶体沿着包含[EuO ₈ ]层的RbEu(MoO ₄ ) ₂的面内方向生长，发光强度达到了5.8倍。