Synthesis Of Series Of Sr₂CeO₄Luminescent Materials By Hydrothermal Method And Their Luminescent Properties

Currently, the rare earth luminescent materials are very popular and have been widelyused in the fields of lighting, display and detection. In1998, Danielson et al synthesized anew blue white emitting phosphor Sr2CeO4, which can be effectively excited by ultraviolet,cathode ray and x-ray, together with high physical and chemistry stability. These indicate thatthe phosphor possesses potential application value.In our present work, a series of Sr2CeO4phosphors were successfully prepared byhydrothermal method. The precursors and the samples were analyzed and characterized byTG-DTA、FTIR、XRD、SEM and fluorescence spectrophotometer. The effect of differentprecipitants, surfactants, dosage of PEG-1000, the doping metal ions and rare earth ions onthe phase structure, morphology and luminescent properties of the samples have beenstudied systematically The following results are obtained.(1) The effects of different precipitants including aqueous ammonia and ammoniumbicarbonate on the phase structure, morphology and luminescent properties of Sr2CeO4phosphors synthesized by hydrothermal method were investigated. The results show that theprecursors obtained by using ((NH4)2CO3and Na2CO3as precipitant respectively have samecrystal phases compositions, which consists of Ce2(CO3)2O·H2O, CeCO3OH and SrCO3,Sr2CeO4crystallites with orthorhombic phase can be obtained after the precursors werecalcined at1000℃for2h. Sr2CeO4particles obtained using (NH4)2CO3as the precipitantshow spherical-like shape and better dispersion, while those obtained using Na2CO3as theprecipitant show irregular shape and serious aggregation. The excitation spectrum ofas-synthesized Sr2CeO4crystallite is a wide band with double peaks in the range of200-400nm. The emission spectrum is a broad band too, which is located in the range of400-600nmwith the main peak at466nm, and it is ascribed to the f�'t1gtransition of Ce4+ions, resultingin a blue-white emission. The luminescent intensity of the sample using (NH4)2CO3as theprecipitant is relatively strong under the main excitation wavelength.(2) The effects of surfactants including PEG-1000, DSASS, CTAB and GL on the phasestructure, morphology and luminescent properties of Sr2CeO4phosphors synthesized by hydrothermal method were investigated. The results show that Sr2CeO4crystallites withorthorhombic phase can be synthesized after the precursors obtained under the four differentsurfactants were calcined at1000℃. The particles obtained using DSASS as the surfactantshow large block structure. While using PEG-1000、CTAB、GL as the surfactants, theparticles show rod-like shape with different slenderness ratio. Different surfactants have greateffects on the intensity of emission peak and excitation peak of the samples, the order fromstrong to weak is PEG-1000> GL>CTAB>DSASS.(3) The effects of hydrothermal reaction time and the dosage of PEG-1000on theproperties of the samples were investigated. The results show that hydrothermal reaction timeand the amount of PEG-1000has little effect on the phase structure, orthorhombic phaseSr2CeO4crystallites can be obtained after the precursors were calcined at1000℃for2h.When the hydrothermal reaction time is6h, the dosage of surfactant PEG-1000is0.2g, theas-synthesized Sr2CeO4phosphors have better crystallization, uniform particles distribution,better dispersity and excellent luminescent performance.(4) In this paper, a series of Sr2CeO4:M doped with non rare earth and rare earth ions,have been synthesized in order to investigate the effect of the doping metal ions on theluminescent properties and find the high-efficient luminescence material. The results showthat doping with metal ions has little effect on shape and position of peaks in emissionspectrum of Sr2CeO4, which is located in the range of400-600nm with main peak at466nm.Among these metal ions, doping with Zn2+or Mg2+can effectively enhance thephotoluminescence of Sr2CeO4phosphor, the appropriate doping concentration of Mg2+andZn2+is4%and5%respectively. Moreover, a red-shift is found in the excitation spectrum ofSr2CeO4phosphor after doping with Zn2+or Mg2+. For rare earth ion Dy3+doped Sr2CeO4phosphors, it is found that the sample shows large hexagon-like granular shape and differencein size, the particle is assembled by countless net structure. The excitation spectrum is a wideband with double peaks, which is similar to that of Sr2CeO4, and the main peak located at305nm. The emission spectrum mainly consists of two parts, the blue emitting band in the rangeof400nm~550nm and the yellow-green emitting peaks in the range of550nm~600nm. The former is mainly due to the emission of Sr2CeO4, while the latter is ascribed to the transitionof4F9/2-6H13/2of Dy3+. The doped-Dy3+concentration has great effect on the fluorescenceintensity and emitting colour of Sr2CeO+4:Dy3. With the increase of Dy3+concentration, theratio of yellow emission to blue emission (RY/B) increases, and the luminescent colourchanges from blue-white to yellow. Meanwhile, the luminescent intensity decrease with theincrease of Dy3+doping concentration, which maybe due to the increase in the degree of latticdistortion caused by Dy3+doping and partly destruction of the one-dimensional chainstructure of Sr2CeO4.