Structure characterization and photoluminescence properties of (Y0.95-xGdxEu0.05)2O3 red phosphors converted from layered rare-earth hydroxide (LRH) nanoflake precursors

(Y0.95-xGdxEu0.05)(2)O-3 red phosphors (x = 0.25-0.95), in both the nanoplate and rounded nanoparticle forms, have been derived from their layered rare-earth hydroxide (LRH) precursors of (Y0.95-xGdxEu0.05)(2)(OH)(5)NO3 center dot nH(2)O synthesized via hydrothermal reactions under neutral pH. Crystal structures and physical properties of the materials are investigated in detail by the combined techniques of XRD, TG, BET, FE-SEM, TEM, and PLE/PL spectroscopies. The LRH precursors crystallize as nanoplates and a higher Gd3+ content produces thinner crystals (down to similar to 5 nm). Calcining the LRHs at 800 degrees C directly yields (Y0.95-xGdxEu0.05)(2)O-3 phosphor nanoplates in the solid solution form. Red-shifting of the charge transfer excitation band (CTB) from similar to 250 to 256 nm was observed with increasing Gd3+. Exciting the phosphors with the peak wavelengths of the CT bands yielded successively weaker Eu3+ emissions despite the decreasing specific surface area of the powder, which was ascribed to the lowered exposure of the close packed (222) facets of the oxide crystals. Nonradiative energy transfer from Gd3+ to Eu3+ was observed upon exciting the phosphors with the S-8(7/2)-I-6(J) transition of Gd3+ at 276 nm, and successively stronger Eu3+ emissions were observed at a higher Gd3+ content. The LRHs nanoplates completely collapse at 1000 degrees C or above to form rounded nanoparticles and a shortened luminescence lifetime and improved internal/external quantum efficiencies were observed at a higher calcination temperature. (C) 2013 Elsevier B. V. All rights reserved.