Hydrothermal Synthesis And Luminescence Behaviors Of （Y,Eu,Gd）₂O₃Red Phosphors

[(Y1-xGdx)0.95Eu0.05]203(0≤x≤0.5) red phosphor powders have been successfully synthesized by hydrothermal precursor synthesis followed by calcination. With rare-earth nitrates as the starting material and urea as the precipitant, hydrothermal treatment (100-180℃,12h) of aqueous solutions of the reactants yielded precursors of three distinctive particle morphologies:submicronspheres(about200nm), microplates (50×5μm), and mixtures of submicronspheres and microplates, depending upon the urea content. The submicron spheres and the microplates were found to have approximate compositions of Ln(OH)CO3-H2O(Ln=Y3+,Eu3+,Gd3+) and Ln2(CO3)3-2H2O respectively. Characterizations of the precursors and the resultant oxide phospors were achieved by field-emission scanning electron microscopy(FE-SEM), Fourier transform infrared spectroscopy(FTIR), X-ray diffractometry(XRD), and photoluminescence excitation/photoluminescence(PLE/PL) spectroscopy. It was found that a calcination temperature of≥800℃is needed to attain a homogeneous [(Y1-xGdx)0.95Eu0.05]203solid solution and thus improved luminescence. Morphology-confined crystal growth of (Yo.95Euo.o5)203was observed from the microplates. The three types of phosphors exhibited a substantial morphology dependent PLE-PL behavior, but did not differ much in the positions of the PLE/PL bands or in the asymmetry factor [I(5D0→7F2)/I(Do0→7F1)] of luminescence. Upon UV excitation into the charge transfer band at250nm, the microplates showed the strongest red emission at613nm (the5D0→7F2transition of Eu3+)at the same calcination temperature of1000℃, whose intensity is2.49and1.57times those of the spheres and the sphere/plate mixture, respectively. Partially replacing Y3+with Gd3+(upto50at.%) while keeping Eu3+at the optimal content of5%substantially improves the613nm red emission.