Pr^(3+)-doped CaAl_(2)O_(4) phosphors with broad yellow emission were synthesized by conventional solid-state reaction in air and their structural and luminescent properties were investigated.A pure monoclinic structu...Pr^(3+)-doped CaAl_(2)O_(4) phosphors with broad yellow emission were synthesized by conventional solid-state reaction in air and their structural and luminescent properties were investigated.A pure monoclinic structure can be obtained when the sintering temperature is 1400℃ or above.With photoluminescence(PL)measurement,the excitation was observed at 450–500 nm,which covered the emission of the blue light-emitting diode(LED)chips.Emission of the phosphors showed a green band and a red band.So these phosphors showed great potential in application of warm white LEDs without reabsorption.Additionally,the optimal emission intensity was obtained when Pr doping level was at 0.2 mol%.Furthermore,the Pr-doped CaAl_(2)O_(4) phosphors have the higher quenching temperature.With an increase in temperature,the emission bands of Pr-doped CaAl_(2)O_(4) showed an abnormal blue-shift.展开更多
In order to effectively improve the afterglow properties of CaAl_(2)O_(4):Eu^(2+),Nd^(3+) phosphors,a series of Ca_(0.982-x)Al_(2)O_(4):0.012 Eu^(2+),0.006 Nd^(3+),xGd^(3+)(x=0,0.012,0.024,0.036,0.048,0.060 mol) phosp...In order to effectively improve the afterglow properties of CaAl_(2)O_(4):Eu^(2+),Nd^(3+) phosphors,a series of Ca_(0.982-x)Al_(2)O_(4):0.012 Eu^(2+),0.006 Nd^(3+),xGd^(3+)(x=0,0.012,0.024,0.036,0.048,0.060 mol) phosphors were prepared by a high-temperature solid-phase approach.Crystalline composition and microstructure were characterized by XRD,TEM,HRTEM,and XPS,luminescence properties were systematically analyzed by fluorescence spectra,afterglow decay curves and TL glow curve.Results show that all of Ca_(0.982-x)Al_(2)O_(4):0.012 Eu^(2+),0.006 Nd^(3+),xGd^(3+)phosphors belong to monoclinic CaAl_(2)O_(4),without other cystalline phase.The blue emission at 442 nm is observed,which is assigned to the 4f^(6)5 d→4f^(7) transition of Eu^(2+) ions.Doping with appropriate amount of Gd^(3+) ions(x=0.036 mol) significantly improves the afterglow properties of phosphors,but the excessive doping of Gd^(3+) induces the fluorescent quenching.The doping of moderate Gd^(3+) changes the traps states,the trap depth varies from 0.598 to 0.644 eV and the trap concentration is also greatly improved,thus significantly improving afterglow performance.展开更多
Combustion catalyst La_(0.8)Sr_(0.2)CoO_3 (LSC) is expected to possess relatively high activity for the oxidation of carbon monoxide and many hydrocarbons. If γ-Al_2O_3 is used as its support, cobalt ions can easily ...Combustion catalyst La_(0.8)Sr_(0.2)CoO_3 (LSC) is expected to possess relatively high activity for the oxidation of carbon monoxide and many hydrocarbons. If γ-Al_2O_3 is used as its support, cobalt ions can easily react with γ-Al_2O_3 at not very high temperature to form spinel CoAl_2O_4 or spinel-like, which decreases the activity of the combustion catalyst. In this paper, MgAl_2O_4 and CaAl_2O_4 were pre-coated on γ-Al_2O_3 by impregnation respectively, which formed compound support for LSC. It is shown that, when MgAl_2O_4 layer is covered on the surface of MgAl_2O_4 by impregnation, the entering of cobalt ions into γ-Al_2O_3 lattice is restrained, then LSC formed on the surface of MgAl_2O_4, which leads to a good catalytic activity of xylene complete oxidation. But the layer of MgAl_2O_4 should be thick enough to reach 30% (mass fraction) MgO in the support due to large size particle of MgAl_2O_4 crystalline. If polyvinyl alcohol (PVA) is added into the impregnation solution adequately, MgAl_2O_4 particles formed on the surface of γ-Al_2O_3 are getting smaller, and less amount of MgAl_2O_4 is needed to cover up the surface of γ-Al_2O_3. If CaAl_2O_4 layer substituted for MgAl_2O_4, more closed cover is obtained in virtue of fine particles of CaAl_2O_4. The activity examination shows that smaller particles of MgAl_2O_4 or CaAl_2O_4 can be more effective to hinder cobalt ions entering the lattice of γ-Al_2O_3, and better activities will be obtained.展开更多
基金supported by the Natural Science Foundation of China(No.51072136)Specialized Research Fund for the Doctoral Program of Higher Education(No.20090072120034).
文摘Pr^(3+)-doped CaAl_(2)O_(4) phosphors with broad yellow emission were synthesized by conventional solid-state reaction in air and their structural and luminescent properties were investigated.A pure monoclinic structure can be obtained when the sintering temperature is 1400℃ or above.With photoluminescence(PL)measurement,the excitation was observed at 450–500 nm,which covered the emission of the blue light-emitting diode(LED)chips.Emission of the phosphors showed a green band and a red band.So these phosphors showed great potential in application of warm white LEDs without reabsorption.Additionally,the optimal emission intensity was obtained when Pr doping level was at 0.2 mol%.Furthermore,the Pr-doped CaAl_(2)O_(4) phosphors have the higher quenching temperature.With an increase in temperature,the emission bands of Pr-doped CaAl_(2)O_(4) showed an abnormal blue-shift.
基金the National Natural Science Fund of China(51772099,51572069,51872091)Scientific and Technological Research Projects of Colleges and Universities in Hebei Province(QN2019049)the Doctoral Initiation Fund(BS2017025)。
文摘In order to effectively improve the afterglow properties of CaAl_(2)O_(4):Eu^(2+),Nd^(3+) phosphors,a series of Ca_(0.982-x)Al_(2)O_(4):0.012 Eu^(2+),0.006 Nd^(3+),xGd^(3+)(x=0,0.012,0.024,0.036,0.048,0.060 mol) phosphors were prepared by a high-temperature solid-phase approach.Crystalline composition and microstructure were characterized by XRD,TEM,HRTEM,and XPS,luminescence properties were systematically analyzed by fluorescence spectra,afterglow decay curves and TL glow curve.Results show that all of Ca_(0.982-x)Al_(2)O_(4):0.012 Eu^(2+),0.006 Nd^(3+),xGd^(3+)phosphors belong to monoclinic CaAl_(2)O_(4),without other cystalline phase.The blue emission at 442 nm is observed,which is assigned to the 4f^(6)5 d→4f^(7) transition of Eu^(2+) ions.Doping with appropriate amount of Gd^(3+) ions(x=0.036 mol) significantly improves the afterglow properties of phosphors,but the excessive doping of Gd^(3+) induces the fluorescent quenching.The doping of moderate Gd^(3+) changes the traps states,the trap depth varies from 0.598 to 0.644 eV and the trap concentration is also greatly improved,thus significantly improving afterglow performance.
文摘Combustion catalyst La_(0.8)Sr_(0.2)CoO_3 (LSC) is expected to possess relatively high activity for the oxidation of carbon monoxide and many hydrocarbons. If γ-Al_2O_3 is used as its support, cobalt ions can easily react with γ-Al_2O_3 at not very high temperature to form spinel CoAl_2O_4 or spinel-like, which decreases the activity of the combustion catalyst. In this paper, MgAl_2O_4 and CaAl_2O_4 were pre-coated on γ-Al_2O_3 by impregnation respectively, which formed compound support for LSC. It is shown that, when MgAl_2O_4 layer is covered on the surface of MgAl_2O_4 by impregnation, the entering of cobalt ions into γ-Al_2O_3 lattice is restrained, then LSC formed on the surface of MgAl_2O_4, which leads to a good catalytic activity of xylene complete oxidation. But the layer of MgAl_2O_4 should be thick enough to reach 30% (mass fraction) MgO in the support due to large size particle of MgAl_2O_4 crystalline. If polyvinyl alcohol (PVA) is added into the impregnation solution adequately, MgAl_2O_4 particles formed on the surface of γ-Al_2O_3 are getting smaller, and less amount of MgAl_2O_4 is needed to cover up the surface of γ-Al_2O_3. If CaAl_2O_4 layer substituted for MgAl_2O_4, more closed cover is obtained in virtue of fine particles of CaAl_2O_4. The activity examination shows that smaller particles of MgAl_2O_4 or CaAl_2O_4 can be more effective to hinder cobalt ions entering the lattice of γ-Al_2O_3, and better activities will be obtained.
