Preparation And Properties Of Eu³⁺ Or Dy³⁺ Ions Doped Gd₂O₃Rare Earth Luminescence Materials With Special Morphologies

Rare earth luminescence materials with special morphologies, It is known that the size，shape and microstructre of inorganic nanomaterials have great influence on their propertiesand applications. The synthesis and property of inorganic nanomaterials （for examplenanowires, nanorod） with special morphologies and microstruetures are of great importancefor the basical and applied research of new inorganic functional materials．So it gets wideattention.Gd₂O₃is a kind of important and accessible rare earth oxides, with excellent physical andchemical stability, and doped with rare earth ions, therefore, Gd₂O₃as matrix is widely usedin rare-earth luminescence materials. The red-emitting Gd₂O₃:Eu³⁺and yellow-emittingGd32O3:Dy+phosphors with special morphologies were prepared by hydrothermal method andhomogeneous precipitation method. TG-DTA, FT-IR, XRD, SEM and Fluorescencespectrophotometer were used to analyze and characterize the formation process, phasestructure, morphology and luminescent properties of the samples. The following results areobtained.（1） The effects of different precipitants including aqueous ammonia and ammoniumbicarbonate on the phase structure, morphology and luminescent properties of Gd₂O₃:Eu³⁺phosphors synthesized by hydrothermal method were investigated. Gd3+2O3:Euphosphorswere synthesized by hydrothermal method using aqueous ammonia and ammoniumbicarbonate as raw materials. The results show that the hydrothermal precursors obtainedrespectively by using aqueous ammonia and ammonium bicarbonate as precipitant areGd（OH）3and Gd2（CO3）3·xH2O respectively. The decomposition process of the two differentprecursors is all divided into three steps. Gd₂O₃:Eu³⁺ crystallites with pure cubic phase can beobtained after the precursors were calcined at800℃for2h. Gd₂O₃:Eu³⁺ particles obtained byusing aqueous ammonia as the precipitant are basically short bar in shape with smallslenderness ratio and uniform size. While Gd₂O₃:Eu³⁺particles obtained by using ammoniumbicarbonate as the precipitant are basically long strips in shape with big slenderness ratio. The main emission peak of as-synthesized Gd3+2O3:Euis at613nm, resulting in a red emission.The luminescent intensity of the sample using ammonium bicarbonate as the precipitant isrelatively strong. The main excitation peak is at261nm, attributed to the charge transfer stateof Eu-O.（2） The effects of surfactants including PEG-1000, DSASS, CTAB and EG on the phasestructure, morphology and luminescent properties of Gd₂O₃:Eu³⁺phosphors synthesized byhydrothermal method were investigated. The results show that Gd₂O₃:Eu³⁺crystallites withpure cubic phase can be synthesized after the precursors obtained under the four differentsurfactants were calcined at800℃. The particles of as-synthesized Gd₂O₃:Eu³⁺are basicallyrods in shape and dispersing well, but the slenderness ratio was different using the fourdifferent surfactants. The particles obtained using PEG-1000as the surfactant are not uniformin size and have a wide range of distribution. While using DSASS、CTAB、EG as thesurfactants, the particles are relatively small in diameter, short in length and have a narrowerrange of distribution. The main emission peak of Gd₂O₃:Eu³⁺rod crystallite is at613nm,which is ascribed to the transition of5D70→F2, resulting in a red emission. A clear red shiftoccurs in the excitation spectrum of Gd₂O₃:Eu³⁺crystallites prepared by the present works,and the main excitation peak is at261nm. Different surfactants have great effects on theintensity of emission peak and excitation peak of the samples, the order from strong to weakis PEG-1000> DSASS> CTAB> EG.（3） The effects of the amount of surfactant （PEG-1000） on the phase structure,morphology and luminescent properties of Gd32O3:Eu+phosphors synthesized byhydrothermal method were investigated. The results show that the amount of PEG-1000haslittle effect on the phase structure, all the Gd32O3:Eu+phosphors have pure cubic crystalstructure. But, the amount of PEG-1000affects particle dispersion and size significantly. Withincreasing amount of PEG-1000, dispersion of Gd₂O₃+3:Euparticles get better and the sizedecreases. The main emission peak of Gd₂O₃:Eu³⁺is at613nm, and the shape and position ofemission spectra are basically same, but the intensity is slightly different. All the excitationspectra consist of three parts, including the charge transfer state （CTB） of Eu³⁺, the f-f transition of Gd3+and the f-f high level transition of Eu³⁺, and the main excitation peak is at261nm.（4） Gd₂O₃:Dy³⁺nanorods were synthesized by hydrothermal method using sodiumhydroxide as the precipitation agent. The results show that the obtained precursor ishexagonal phase gadolinium （dysprosium） hydroxide. Gd₂O₃:Dy³⁺with pure cubic phase canbe obtained after the precursors were calcined at900℃. The Gd3+2O3:Dysamples arenanorods with a diameter about100nm and a length about500nm-1μm. The excitationspectrum is composed of a series of peaks located at239nm,279nm,314nm and353nmrespectively, and the strongest peak is at279nm. The emission spectrum mainly consists oftwo parts, the blue emitting peaks （band） in the range of460nm-500nm and the yellow-greenemitting peaks （band） in the range of560nm-590nm. All the peaks （bands） are ascribed tothe characteristic emission of Dy³⁺. The intensity of the latter emitting peaks （band） was muchstronger than that of the former; therefore, the samples show yellow-light emitting under theexcitation of ultraviolet light.（5） New yellow-emitting phosphors Gd₂O₃+3:Dywere prepared by hydrothermal methodusing urea as the precipitation agent. The results show that the precursor is Gd2（CO3）3·xH2O.Gd₂O₃:Dy³⁺with pure cubic phase can be obtained after the precursor was calcined at900℃.The micrograph of sample shows needle in shape with a diameter about500nm-1.3μm and alength about10μm-200μm. The concentration of doping-Dy³⁺has great effect on thefluorescence intensity of Gd₂O₃:Dy³⁺, the fluorescence intensity increases with thedoped-Dy³⁺concentration, then decrease. The strongest fluorescence intensity can be obtainedwhen the doping concentration is0.8%. The concentration quenching is mainly caused by theinteraction of dipole-dipole.（6） Spherical Gd₂O₃:Dy³⁺phosphors were synthesized by homogeneous precipitationmethod using urea as the precipitation agent. The results show that the obtained precursor isGd2（CO3）3·xH2O with a diameter about410nm. Gd₂O₃:Dy³⁺with pure cubic phase can beobtained after the precursors were calcined at900℃. And the phosphors are spherical inshape with a diameter about300nm. Under the excitation of279nm, the main emission peak is at573nm, showing yellow-light emitting.