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

Abstract: (Y0.95Eu0.05)2O3 red phosphor particles with three distinctive morphologies of submicron spheres (up to 180nm), microflowers (up to 10μm) and microplates (up to 50×10μm) have been converted from their respective precursors autoclaved (100–180°C, 12h) 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 (400) 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 ∼240nm the microplates showed the strongest red emission at ∼613nm (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±0.1ms for the 613nm emission of the three morphologies, suggesting that the differing luminescence was largely morphology-dependent, rather than defect-dependent. [Copyright &y& Elsevier]