The Zn1-xAl2 O4:xEu2+ phosphor powders were synthesized by the solid-state reaction method.The synthesis temperature for ZnAl2 O4 was optimized,whereas the phase structure,TEM images,photoluminescence(PL) properti...The Zn1-xAl2 O4:xEu2+ phosphor powders were synthesized by the solid-state reaction method.The synthesis temperature for ZnAl2 O4 was optimized,whereas the phase structure,TEM images,photoluminescence(PL) properties,the concentration quenching mechanism,the fluorescence decay curves,as well as the CIE chromaticity coordinates of the samples were investigated in details.Under the excitation at 379 nm,the phosphor exhibits an asymmetric broad-band green emission with a peak at 532 nm,which is ascribed to the 5 d-4 f transition of Eu2+.When the doping concentration of Eu2+ ions is 0.01,the luminescence intensity of the sample reaches the maximum value.It is further proved that the exchange interaction results in the concentration quenching of Eu2+ in the Zn1-xAl2 O4:xEu2+ phosphor powders.The thermal quenching property of ZnAl2 O4:Eu2+phosphor was investigated and the quantum efficiency(QE) values of the selected Zn0.99Al2 O4:0.01 Eu2+ phosphor was measured and determined as 54.85%.The lifetime of the optimized sample Zn0.99Al2 O4:0.01 Eu2+ is 3.0852 μs and the CIE coordinate of the sample was calculated as(0.3323,0.5538) with high-color-purity green emission.All properties indicate that the green-emitting ZnAl2 O4:Eu2+ phosphor powder has potential application in white LEDs.展开更多
In this paper, a series of zinc cobaltite catalysts with the general formula Znx-Co1-xCo2O4 (x = 0.25, 0.50, 0.75 and 1.0) has been prepared using the co-precipitation method. Thermal analyzes (TGA and DTA) were used ...In this paper, a series of zinc cobaltite catalysts with the general formula Znx-Co1-xCo2O4 (x = 0.25, 0.50, 0.75 and 1.0) has been prepared using the co-precipitation method. Thermal analyzes (TGA and DTA) were used to follow up the thermal events accompanying the heat treatment of the parent mixture. Based on these results, the various parent mixtures were calcined at 500℃. The obtained solid catalysts were characterized by using XRD, FT-IR and N2-adsorption. The catalytic decomposition of N2O to N2 and O2 was carried out on the zinc-cobaltite catalysts. It was found that partial replacement of Co2+ by Zn2+ in Co3O4 spinel oxide led to a significant improvement in their N2O decomposition activity. Moreover, the catalytic activity was found to be depended on the calcination temperature utilized.展开更多
The structures of the Mn-Zn ferrites synthesized under different sintering conditions by the sol-gel method were investigated by the X-ray diffraction (XRD) and the scanning electron microscopy (SEM) with focus on...The structures of the Mn-Zn ferrites synthesized under different sintering conditions by the sol-gel method were investigated by the X-ray diffraction (XRD) and the scanning electron microscopy (SEM) with focus on two factors: the pre-sintering treatment and the calcining time. The results show that the sintering conditions have significant effects on the structures and the particle size of the Mn-Zn ferrites. Compared with the products without pre-sintering, those pre-sintered at 500℃ have a single phase and no diffraction peaks of Fe2O3 that could be found. The effects of the pre-sintering temperature on the structures of the ferrites were also studied. As a result, 500℃ proves to be the favorite in the pre-sintering treatment. The XRD patterns of the ferrites calcined at 1 200℃ for 6 h will present diffraction peaks of pure crystallization of spinel phase while those for 2 h or 4 h will show peaks of Fe2O3. The SEM also bears witness to well-grown grains of pure Mn-Zn ferrites if calcined for 6 hours.展开更多
The nanometer materials ZnFe 2O 4 was prepared by tartaric acid sol gel method,its grain size is around 60~10nm.The effects of sintered condition on the crystal structure and particle size of ZnFe 2O 4 were investiga...The nanometer materials ZnFe 2O 4 was prepared by tartaric acid sol gel method,its grain size is around 60~10nm.The effects of sintered condition on the crystal structure and particle size of ZnFe 2O 4 were investigated.The sample was characterized by XRD and TEM.展开更多
基金Project supported by the National Natural Science Foundation of China(51472222,51372232)the Fundamental Research Fund for the Central Universities(2652017362)
文摘The Zn1-xAl2 O4:xEu2+ phosphor powders were synthesized by the solid-state reaction method.The synthesis temperature for ZnAl2 O4 was optimized,whereas the phase structure,TEM images,photoluminescence(PL) properties,the concentration quenching mechanism,the fluorescence decay curves,as well as the CIE chromaticity coordinates of the samples were investigated in details.Under the excitation at 379 nm,the phosphor exhibits an asymmetric broad-band green emission with a peak at 532 nm,which is ascribed to the 5 d-4 f transition of Eu2+.When the doping concentration of Eu2+ ions is 0.01,the luminescence intensity of the sample reaches the maximum value.It is further proved that the exchange interaction results in the concentration quenching of Eu2+ in the Zn1-xAl2 O4:xEu2+ phosphor powders.The thermal quenching property of ZnAl2 O4:Eu2+phosphor was investigated and the quantum efficiency(QE) values of the selected Zn0.99Al2 O4:0.01 Eu2+ phosphor was measured and determined as 54.85%.The lifetime of the optimized sample Zn0.99Al2 O4:0.01 Eu2+ is 3.0852 μs and the CIE coordinate of the sample was calculated as(0.3323,0.5538) with high-color-purity green emission.All properties indicate that the green-emitting ZnAl2 O4:Eu2+ phosphor powder has potential application in white LEDs.
文摘In this paper, a series of zinc cobaltite catalysts with the general formula Znx-Co1-xCo2O4 (x = 0.25, 0.50, 0.75 and 1.0) has been prepared using the co-precipitation method. Thermal analyzes (TGA and DTA) were used to follow up the thermal events accompanying the heat treatment of the parent mixture. Based on these results, the various parent mixtures were calcined at 500℃. The obtained solid catalysts were characterized by using XRD, FT-IR and N2-adsorption. The catalytic decomposition of N2O to N2 and O2 was carried out on the zinc-cobaltite catalysts. It was found that partial replacement of Co2+ by Zn2+ in Co3O4 spinel oxide led to a significant improvement in their N2O decomposition activity. Moreover, the catalytic activity was found to be depended on the calcination temperature utilized.
文摘The structures of the Mn-Zn ferrites synthesized under different sintering conditions by the sol-gel method were investigated by the X-ray diffraction (XRD) and the scanning electron microscopy (SEM) with focus on two factors: the pre-sintering treatment and the calcining time. The results show that the sintering conditions have significant effects on the structures and the particle size of the Mn-Zn ferrites. Compared with the products without pre-sintering, those pre-sintered at 500℃ have a single phase and no diffraction peaks of Fe2O3 that could be found. The effects of the pre-sintering temperature on the structures of the ferrites were also studied. As a result, 500℃ proves to be the favorite in the pre-sintering treatment. The XRD patterns of the ferrites calcined at 1 200℃ for 6 h will present diffraction peaks of pure crystallization of spinel phase while those for 2 h or 4 h will show peaks of Fe2O3. The SEM also bears witness to well-grown grains of pure Mn-Zn ferrites if calcined for 6 hours.
文摘The nanometer materials ZnFe 2O 4 was prepared by tartaric acid sol gel method,its grain size is around 60~10nm.The effects of sintered condition on the crystal structure and particle size of ZnFe 2O 4 were investigated.The sample was characterized by XRD and TEM.