Investigation On The Preparation And Fluorescent Properties Of Monodisperse Spherical Dy³⁺ Doping Y₂O₃/Gd₂O₃ Phosphors

The Dy³⁺ doping Y₂O₃/Gd₂O₃ phosphors were obtained through precursor synthesis via carbonate homogeneous precipitation using rare earth nitrates as mother salt and urea as precipitating agent, followed by calcination at 600-1300 ℃. The synthesis, particle size control, crystal structure stabilization, fluorescence properties and energy transfer studied systematically in a wide range（Dy/Ln=0-10 at%, Ln=Y+Gd+Dy）. The following main conclusions have been reached:（1） The monodisperse spherical (Y_1-xDy_x)₂O₃ precursor particles were synthesized by homogeneous precipitation technique. From which it can be seen that all the precursors were amorphous with approximate composition of(Y_1-xDy_x)（OH）（CO₃）·1.4H₂O whose size can be controlled by adjusting the urea content. The phase pure(Y_1-xDy_x)₂O₃ can be obtained by annealing at 600 ℃, and the monodisperse spherical morphology can be kept even at higher temperature of 1000 ℃, while the spherical morphology was destroyed when the calcination temperature increases up to 1200 ℃. The(Y_1-xDy_x)₂O₃ phosphor particles exhibit strong yellow emission and weak blue emission(corresponding to 4F9/2→6H13/2 and 4F9/2→6H15/2 transition of Dy³⁺ respectively) upon UV excitation at 352 nm(6H15/2→6P7/2 transition of Dy³⁺). The luminescent property of the phosphors can be improved with the temperature increasing and the quenching concentration of Dy³⁺ is found to be 2 at%.（2） The monodisperse spherical(Gd_1-xDy_x)₂O₃ precursor particles were synthesized by homogeneous precipitation technique. All the precursors were amorphous with approximate composition of(Gd_1-xDy_x)（OH）（CO₃）·1.3H₂O. The precursor particle size can be controlled by adjusting the urea content and partially replacing deionized water with organic solvent as the reaction solution. The(Gd_1-xDy_x)₂O₃ phosphor particles exhibit strong yellow emission and weak blue emission(corresponding to 4F9/2→6H13/2 and 4F9/2→6H15/2 transition of Dy³⁺ respectively) upon UV excitation at 275 nm(8S7/2→6IJ transition of Gd³⁺) and the quenching concentration of Dy³⁺ is found to be 2 at%. Owing to the energy transfer of Gd³⁺→Dy³⁺ the fluorescence intensity of the phosphor was significantly improved, and increased with the calcination temperature increasing. Fluorescence decay for the 575 nm emission of(Gd_1-xDy_x)₂O₃ reduced gradually with the Dy³⁺ content and calcination temperature increasing. The former is mainly due to the energy transfer between Dy³⁺, while the latter is attributed to the improved crystallinity of phosphor particles. A cubic phase to monoclinic phase transition of Gd₂O₃ was found when the calcination temperature was fixed at 1300 ℃. Based on this, doping with smaller ionic radius Y³⁺ was proposed to stabilize the lattice structure of Gd₂O₃ and the minimum doping amount was determined to be 5 at%.（3） The monodisperse spherical [(Y_yGd_1-y)_1-xDy_x]₂O₃ precursor particles were synthesized by homogeneous precipitation technique. All precursors were amorphous with approximate composition of [(Y_yGd_1-y)_1-xDy_x]（OH）（CO₃）·1.5H₂O. All precursors have good monodisperse spherical morphology and the morphology can be kept even at higher temperature of 1000 ℃. The differential precipitation of Y³⁺ and Gd³⁺ was found by TG analysis. The [(Y_yGd_1-y)_1-xDy_x]₂O₃ phosphor particles exhibit strong yellow emission(4F9/2→6H13/2 transition of Dy³⁺) upon UV excitation at 275 nm(8S7/2→6IJ transition of Gd³⁺), and the yellow emission intensity is stronger than that of blue emission. The high efficient energy transfer between Gd³⁺→Dy³⁺ can improve the fluorescence properties of phosphors, which can be defined by the comparison of [(Y_y Gd_1-y)_0.98Dy_0.02]₂O₃ and(Y_0.98Dy_0.02)₂O₃.