Morphology-dependent crystallization and luminescence behavior of (Y, Eu)(2)O-3 red phosphors

(Y0.95Eu0.05)(2)O-3 red phosphor particles with three distinctive morphologies of submicron spheres (up to 180 nm), microflowers (up to 10 mu m) and microplates (up to 50 x 10 mu m) have been converted from their respective precursors autoclaved (100-180 degrees C, 12 h) from mixed solutions of the component nitrates and hexamethylenetetramine [(CH2)(6)N-4]. The three types of precursors were found to have the approximate compositions M(OH)CO3 center dot H2O for the sphere (M = Y and Eu), M4O(OH)(9)NO3 for the flower and M-2(CO3)(3)center dot 3H(2)O for the plate, and their formation domains were defined. Both X-ray diffraction and photoluminescence analysis indicated that a calcination temperature of >= 800 degrees C is needed to attain a homogeneous (Y0.95Eu0.05)(2)O-3 solid solution and thus improved luminescence. Morphology-confined crystal growth of (Y0.95Eu0.05)(2)O-3 was observed from the microplates, yielding a significantly higher exposure of the (4 0 0) facets at elevated temperature. The three types of phosphors exhibited a substantial morphology-dependent photoluminescence (PL)/photolumineseence excitation (PLE) behavior, but did not differ much in the positions of the PLE/PL bands or in the asymmetry factor [I(D-5(0) -> F-7(2))/I(D-5(0) -> F-7(1))] of the luminescence. Upon UV excitation into the charge transfer band at similar to 240 nm the microplates showed the strongest red emission at similar to 613 nm (the D-5(0) -> F-7(2) transition of Eu3+) at a calcination temperature of 1000 degrees C, whose intensity was similar to 2.49 and 1.57 times those of the flowers and spheres, respectively. Fluorescence decay analysis yielded similar lifetimes of similar to 1.5 +/- 0.1 ms for the 613 nm emission of the three morphologies, suggesting that the differing luminescence was largely morphology-dependent, rather than defect-dependent. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.