Layered rare-earth hydroxide and oxide nanoplates of the Y/Tb/Eu system: phase-controlled processing, structure characterization and color-tunable photoluminescence via selective excitation and efficient energy transfer

Well-crystallized (Y(0.97−x)Tb(0.03)Eu(x))(2)(OH)(5)NO(3)·nH(2)O (x = 0–0.03) layered rare-earth hydroxide (LRH) nanoflakes of a pure high-hydration phase have been produced by autoclaving from the nitrate/NH(4)OH reaction system under the optimized conditions of 100 °C and pH ∼7.0. The flakes were then converted into (Y(0.97−x)Tb(0.03)Eu(x))(2)O(3) phosphor nanoplates with color-tunable photoluminescence. Detailed structural characterizations confirmed that LRH solid solutions contained NO(3)(−) anions intercalated between the layers. Characteristic Tb(3+) and Eu(3+) emissions were detected in the ternary LRHs by selectively exciting the two types of activators, and the energy transfer from Tb(3+) to Eu(3+) was observed. Annealing the LRHs at 1100 °C produced cubic-lattice (Y(0.97−x)Tb(0.03)Eu(x))(2)O(3) solid-solution nanoplates with exposed 222 facets. Multicolor, intensity-adjustable luminescence was attained by varying the excitation wavelength from ∼249 nm (the charge transfer excitation band of Eu(3+)) to 278 nm (the 4f(8)–4f(7)5d(1) transition of Tb(3+)). Unitizing the efficient Tb(3+) to Eu(3+) energy transfer, the emission color of (Y(0.97−x)Tb(0.03)Eu(x))(2)O(3) was tuned from approximately green to yellowish-orange by varying the Eu(3+)/Tb(3+) ratio. At the optimal Eu(3+) content of x = 0.01, the efficiency of energy transfer was ∼91% and the transfer mechanism was suggested to be electric multipole interactions. The phosphor nanoplates developed in this work may be incorporated in luminescent films and find various lighting and display applications.