Two-Dimensional-Layered Perovskite ALaTa₂O₇:Bi³⁺ (A = K and Na) Phosphors with Versatile Structures and Tunable Photoluminescence

Topological chemical reaction methods are indispensable for fabricating new materials or optimizing their functional properties, which is particularly important for two-dimensional (2D)-layered compounds with versatile structures. Herein, we demonstrate a low-temperature (∼350 °C) ion exchange approach to prefabricate metastable phosphors ALa1–xTa2O7:xBi3+ (A = K and Na) with RbLa1–xTa2O7:xBi3+ serving as precursors. The as-prepared ALa0.98Ta2O7:0.02 Bi3+ (A = Rb, K, and Na) share the same Dion–Jacobson type 2D-layered perovskite phase, and photoluminescence analyses show that ALa0.98Ta2O7:0.02 Bi3+ (A = Rb, K, and Na) phosphors exhibit broad emission bands peaking at 540, 550, and 510 nm, respectively, which are attributed to the nonradiative transition of Bi3+ from excited state 3P1 or 3P0 to ground state 1S0. The various Bi3+ local environments at the crystallographic sites enable the different distributions of emission and excitation spectra, and the photoluminescence tuning of ALa0.98Ta2O7:0.02 Bi3+ (A = Rb, K, and Na) phosphors are realized through alkali metal ion exchange. Notably, the combination of superior trivalent bismuth emission and low-temperature ion exchange synthesis leads to a novel yellow-emitting K(La0.98Bi0.02)Ta2O7 phosphor which is successfully applied in a white LED device based on a commercially available 365 nm LED chip. Our realizable cases of this low-temperature ion exchange strategy could promote exploration into metastable phosphors with intriguing properties.