Hexagonal WO3 nanorods are fabricated by a facile hydrothermal process at 180 ℃ using sodium tungstate and sodium chloride as starting materials. The morphology, structure, and composition of the prepared nanorods ar...Hexagonal WO3 nanorods are fabricated by a facile hydrothermal process at 180 ℃ using sodium tungstate and sodium chloride as starting materials. The morphology, structure, and composition of the prepared nanorods are studied by scanning electron microscopy, X-ray diffraction spectroscopy, and energy dispersive spectroscopy. It is found that the agglomeration of the nanorods is strongly dependent on the PH value of the reaction solution. Uniform and isolated WO3 nanorods with diameters ranging from 100 nm-150 nm and lengths up to several micrometers are obtained at PH = 2.5 and the nanorods are identified as being hexagonal in phase structure. The sensing characteristics of the WO3 nanorod sensor are obtained by measuring the dynamic response to NO2 with concentrations in the range 0.5 ppm-5 ppm and at working temperatures in the range 25 ℃-250 ℃. The obtained WO3 nanorods sensors are found to exhibit opposite sensing behaviors, depending on the working temperature. When being exposed to oxidizing NO2 gas, the WO3 nanorod sensor behaves as an n-type semiconductor as expected when the working temperature is higher than 50 ℃, whereas, it behaves as a p-type semiconductor below 50 ℃. The origin of the n- to p-type transition is correlated with the formation of an inversion layer at the surface of the WO3 nanorod at room temperature. This finding is useful for making new room temperature NO2 sensors based on hexagonal WO3 nanorods.展开更多
Hexagonal WO_3 nanorods were synthesized through a facile hydrothermal method. The nanorods properties were investigated by scanning electron microscope（SEM）, transmission electron microscope（TEM）, energy dispersi...Hexagonal WO_3 nanorods were synthesized through a facile hydrothermal method. The nanorods properties were investigated by scanning electron microscope（SEM）, transmission electron microscope（TEM）, energy dispersive spectroscopy（EDS）, and x-ray diffraction（XRD）. The NO_2-sensing performances in terms of sensor response, response/recovery times and repeatability at room temperature were optimized by varying the heat treatment temperature of WO_3 nanorods. The optimized NO_2sensor（400-℃-annealed WO_3 nanorods） showed an ultra-high sensor response of 3.2 and short response time of 1 s to 5-ppm NO_2. In addition, the 400-℃-annealed sample exhibited more stable repeatability.Furthermore, dynamic responses measurements of annealed samples showed that all the annealed WO_3 nanorods sensors presented p-type behaviors. We suppose the p-type behavior of the WO_3 nanorods sensor to be that an inversion layer is formed in the space charge layer when the sensor is exposed to NO_2 at room temperature.Therefore, the 400-℃-annealed WO_3 nanorods sensor is one of the most energy conservation candidates to detect NO_2 at room temperature.展开更多
In order to improve the luminescence properties of CaTiO3：Pr3＋, a series of CaTiO3：Pr3＋, such as CaTi0.97Nb0.03O3：Pr3＋, Ca0.8Zn0.2TiO3： Pr3＋, Ca0.8Zn0.2Ti0.97Nb0.03O3：Pr3＋ and B3＋-doped Ca0.8Zn0.2Ti0.97Nb0....In order to improve the luminescence properties of CaTiO3：Pr3＋, a series of CaTiO3：Pr3＋, such as CaTi0.97Nb0.03O3：Pr3＋, Ca0.8Zn0.2TiO3： Pr3＋, Ca0.8Zn0.2Ti0.97Nb0.03O3：Pr3＋ and B3＋-doped Ca0.8Zn0.2Ti0.97Nb0.03O3： Pr3＋ were prepared through conventional solid state reaction method. The results of the photoluminescence excitation and emission spectra showed that all the samples emitted red phosphorescence at 612 nm originating from 1D2 to 3H4 emission of Pr3＋ under the 337 nm excitation. When examined by the X-ray diffraction （XRD）, all the samples presented a predominant phase of CaTiO3 （JCPDS# 42-423） except Zn2＋-doped samples which also revealed another phase of Zn2Ti3O8 （JCPDS# 73-579）. The results of the afterglow decay curves showed that co-doping Zn2＋ ions, Nb5＋ ions or adding a small amount of B3＋ into Ca0.8Zn0.2Ti0.97Nb0.03O3：Pr3＋ were effective in improving the photoluminescence properties of CaTiO3：Pr3＋ phosphor. Thermoluminescence results showed that the trap existing in all the samples was the same as in CaTiO3：Pr3＋ and doping singly Nb5＋ or Zn2＋ hardly changed the trap depth but co-doping Nb5＋ and Zn2＋ could modify the trapping level from 0.63 to 1.26 eV distinctively. In addition, adding a certain amount of B3＋ into CTO-PZN could also deepen the trap depth.展开更多
Nb5＋ doped Ca0.8Zn0.2TiO3：Pr3＋ red long afterglow phosphors were synthesized by solid-state reaction methods. X-ray diffraction, photoluminescence spectroscopy and thermally stimulated spectrometry were used to inv...Nb5＋ doped Ca0.8Zn0.2TiO3：Pr3＋ red long afterglow phosphors were synthesized by solid-state reaction methods. X-ray diffraction, photoluminescence spectroscopy and thermally stimulated spectrometry were used to investigate the effects of Nb5＋ content on the crystal characteristics and luminescent properties of Ca0.8Zn0.2Ti1-xNbxO3：Pr3＋ phosphors. The results showed that the addition of a small quantity of Nb5＋ had negligible effect on the crystal characteristics of Ca0.8Zn0.2Ti1-xNbxO3：Pr3＋, but it could change the trapping parameters （the depth of trap, frequency factors and the concentration of trapped charges at t=0） of Ca0.8Zn0.2Ti1-xNbxO3：Pr3＋ phosphors, and then led to the enhance-ment of red fluorescence and phosphorescence at 612 nm originating from 1D2→3H4 transition of Pr3＋. Both of the red fluorescence intensity and afterglow time reached the largest values in the sample of Ca0.8Zn0.2Ti1-xNbxO3：Pr3＋ with x=0.05. The afterglow time of Ca0.8Zn0.2Ti0.95Nb0.05O3：Pr3＋ phosphors lasted for over 24 min （≥1 mcd/m2） when the excited source was cut off.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.60771019,61271070,and 61274074)the Tianjin Key Research Program of Application Foundation and Advanced Technology,China(Grant No.11JCZDJC15300)
文摘Hexagonal WO3 nanorods are fabricated by a facile hydrothermal process at 180 ℃ using sodium tungstate and sodium chloride as starting materials. The morphology, structure, and composition of the prepared nanorods are studied by scanning electron microscopy, X-ray diffraction spectroscopy, and energy dispersive spectroscopy. It is found that the agglomeration of the nanorods is strongly dependent on the PH value of the reaction solution. Uniform and isolated WO3 nanorods with diameters ranging from 100 nm-150 nm and lengths up to several micrometers are obtained at PH = 2.5 and the nanorods are identified as being hexagonal in phase structure. The sensing characteristics of the WO3 nanorod sensor are obtained by measuring the dynamic response to NO2 with concentrations in the range 0.5 ppm-5 ppm and at working temperatures in the range 25 ℃-250 ℃. The obtained WO3 nanorods sensors are found to exhibit opposite sensing behaviors, depending on the working temperature. When being exposed to oxidizing NO2 gas, the WO3 nanorod sensor behaves as an n-type semiconductor as expected when the working temperature is higher than 50 ℃, whereas, it behaves as a p-type semiconductor below 50 ℃. The origin of the n- to p-type transition is correlated with the formation of an inversion layer at the surface of the WO3 nanorod at room temperature. This finding is useful for making new room temperature NO2 sensors based on hexagonal WO3 nanorods.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.60771019,61271070,and 61274074)the Tianjin Key Research Program of Application Foundation and Advanced Technology,China(Grant No.11JCZDJC15300)
文摘Hexagonal WO_3 nanorods were synthesized through a facile hydrothermal method. The nanorods properties were investigated by scanning electron microscope（SEM）, transmission electron microscope（TEM）, energy dispersive spectroscopy（EDS）, and x-ray diffraction（XRD）. The NO_2-sensing performances in terms of sensor response, response/recovery times and repeatability at room temperature were optimized by varying the heat treatment temperature of WO_3 nanorods. The optimized NO_2sensor（400-℃-annealed WO_3 nanorods） showed an ultra-high sensor response of 3.2 and short response time of 1 s to 5-ppm NO_2. In addition, the 400-℃-annealed sample exhibited more stable repeatability.Furthermore, dynamic responses measurements of annealed samples showed that all the annealed WO_3 nanorods sensors presented p-type behaviors. We suppose the p-type behavior of the WO_3 nanorods sensor to be that an inversion layer is formed in the space charge layer when the sensor is exposed to NO_2 at room temperature.Therefore, the 400-℃-annealed WO_3 nanorods sensor is one of the most energy conservation candidates to detect NO_2 at room temperature.
基金supported by the National Natural Science Foundation of China (51072128)
文摘In order to improve the luminescence properties of CaTiO3：Pr3＋, a series of CaTiO3：Pr3＋, such as CaTi0.97Nb0.03O3：Pr3＋, Ca0.8Zn0.2TiO3： Pr3＋, Ca0.8Zn0.2Ti0.97Nb0.03O3：Pr3＋ and B3＋-doped Ca0.8Zn0.2Ti0.97Nb0.03O3： Pr3＋ were prepared through conventional solid state reaction method. The results of the photoluminescence excitation and emission spectra showed that all the samples emitted red phosphorescence at 612 nm originating from 1D2 to 3H4 emission of Pr3＋ under the 337 nm excitation. When examined by the X-ray diffraction （XRD）, all the samples presented a predominant phase of CaTiO3 （JCPDS# 42-423） except Zn2＋-doped samples which also revealed another phase of Zn2Ti3O8 （JCPDS# 73-579）. The results of the afterglow decay curves showed that co-doping Zn2＋ ions, Nb5＋ ions or adding a small amount of B3＋ into Ca0.8Zn0.2Ti0.97Nb0.03O3：Pr3＋ were effective in improving the photoluminescence properties of CaTiO3：Pr3＋ phosphor. Thermoluminescence results showed that the trap existing in all the samples was the same as in CaTiO3：Pr3＋ and doping singly Nb5＋ or Zn2＋ hardly changed the trap depth but co-doping Nb5＋ and Zn2＋ could modify the trapping level from 0.63 to 1.26 eV distinctively. In addition, adding a certain amount of B3＋ into CTO-PZN could also deepen the trap depth.
基金Project supported by the National Natural Science Foundation of China (51072128)Key Research Project of Science and Technology of Shanxi (20110321040-01)Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxi
文摘Nb5＋ doped Ca0.8Zn0.2TiO3：Pr3＋ red long afterglow phosphors were synthesized by solid-state reaction methods. X-ray diffraction, photoluminescence spectroscopy and thermally stimulated spectrometry were used to investigate the effects of Nb5＋ content on the crystal characteristics and luminescent properties of Ca0.8Zn0.2Ti1-xNbxO3：Pr3＋ phosphors. The results showed that the addition of a small quantity of Nb5＋ had negligible effect on the crystal characteristics of Ca0.8Zn0.2Ti1-xNbxO3：Pr3＋, but it could change the trapping parameters （the depth of trap, frequency factors and the concentration of trapped charges at t=0） of Ca0.8Zn0.2Ti1-xNbxO3：Pr3＋ phosphors, and then led to the enhance-ment of red fluorescence and phosphorescence at 612 nm originating from 1D2→3H4 transition of Pr3＋. Both of the red fluorescence intensity and afterglow time reached the largest values in the sample of Ca0.8Zn0.2Ti1-xNbxO3：Pr3＋ with x=0.05. The afterglow time of Ca0.8Zn0.2Ti0.95Nb0.05O3：Pr3＋ phosphors lasted for over 24 min （≥1 mcd/m2） when the excited source was cut off.
