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 (Y0.97-xTb0.03Eux)(2)(OH)(5)NO3 center dot 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/NH4OH reaction system under the optimized conditions of 100 degrees C and pH similar to 7.0. The flakes were then converted into (Y0.97-xTb0.03Eux)(2)O-3 phosphor nanoplates with color-tunable photoluminescence. Detailed structural characterizations confirmed that LRH solid solutions contained NO3- anions intercalated between the layers. Characteristic Tb3+ and Eu3+ emissions were detected in the ternary LRHs by selectively exciting the two types of activators, and the energy transfer from Tb3+ to Eu3+ was observed. Annealing the LRHs at 1100 degrees C produced cubic-lattice (Y0.97-xTb0.03Eux)(2)O-3 solid-solution nanoplates with exposed 222 facets. Multicolor, intensity-adjustable luminescence was attained by varying the excitation wavelength from similar to 249 nm (the charge transfer excitation band of Eu3+) to 278 nm (the 4f(8)-4f(7)5d(1) transition of Tb3+). Unitizing the efficient Tb3+ to Eu3+ energy transfer, the emission color of (Y0.97-xTb0.03Eux)(2)O-3 was tuned from approximately green to yellowish-orange by varying the Eu3+/Tb3+ ratio. At the optimal Eu3+ content of x = 0.01, the efficiency of energy transfer was similar to 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.