Morphology-dependent crystallization and luminescence behavior of (Y, Eu)2O3 red phosphors

(Y0.95Eu0.05)2O3 red phosphor particles with three distinctive morphologies of submicron spheres (up to 180 nm), microflowers (up to 10 μm) and microplates (up to 50 × 10 μm) have been converted from their respective precursors autoclaved (100–180 °C, 12 h) from mixed solutions of the component nitrates and hexamethylenetetramine [(CH2)6N4]. The three types of precursors were found to have the approximate compositions M(OH)CO3·H2O for the sphere (M = Y and Eu), M4O(OH)9NO3 for the flower and M2(CO3)3·3H2O for the plate, and their formation domains were defined. Both X-ray diffraction and photoluminescence analysis indicated that a calcination temperature of ⩾800 °C is needed to attain a homogeneous (Y0.95Eu0.05)2O3 solid solution and thus improved luminescence. Morphology-confined crystal growth of (Y0.95Eu0.05)2O3 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)/photoluminescence excitation (PLE) behavior, but did not differ much in the positions of the PLE/PL bands or in the asymmetry factor [I(5D0 → 7F2)/I(5D0 → 7F1)] of the luminescence. Upon UV excitation into the charge transfer band at ∼240 nm the microplates showed the strongest red emission at ∼613 nm (the 5D0 → 7F2 transition of Eu3+) at a calcination temperature of 1000 °C, whose intensity was ∼2.49 and 1.57 times those of the flowers and spheres, respectively. Fluorescence decay analysis yielded similar lifetimes of ∼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.