Y3Al5O12∶Eu nanophosphors were synthesized by a gel combustion method. The structure of phosphors was characterized by XRD and FTIR. YAG phase came to occur when YAG∶Eu precursors were sintered at 800 ℃, although t...Y3Al5O12∶Eu nanophosphors were synthesized by a gel combustion method. The structure of phosphors was characterized by XRD and FTIR. YAG phase came to occur when YAG∶Eu precursors were sintered at 800 ℃, although the phase was mainly amorphous. The organic groups pyrolyzed completely and pure YAG phase was obtained in the samples sintered at 900 ℃. In the formation of YAG phase, no intermediate phases such as YAP and YAM were detected. Both 5D0 → 7F1 orange and 5D0 → 7F2 red emission could be observed for all the sintered samples. However, the emission of amorphous samples was greatly different from that of crystalline ones. The former was mainly 5D0 → 7F2 red emission, but the latter was 5D0 → 7F1 orange emission. As sintering temperature rises, the ratio of orange to red for phosphors increases. Eu could be doped up to 8% in YAG host lattice, and fluorescence quenching was absent. It indicated that the gel combustion synthesis method can increase emission intensity and quenching concentration due to a good distribution of Eu3+ activators in Y3Al5O12 matrix.展开更多
The transport properties were studied for rare earth manganese oxide La_(0.67)Ca_(0.33)Mn_(1-x)Fe_xO_3 (x=0～0.3) systems. It is found that with increasing Fe^(3+)-doping content x, the resistance increases and the in...The transport properties were studied for rare earth manganese oxide La_(0.67)Ca_(0.33)Mn_(1-x)Fe_xO_3 (x=0～0.3) systems. It is found that with increasing Fe^(3+)-doping content x, the resistance increases and the insulator-metal transition temperature (T_(IM)) shifts to lower temperature. If the doping content is small, the transport properties manifest metallic characteristics in the temperature range of T<T_(IM), while they will obey a thermal activation model in the temperature range of T>T_(IM). Such a behavior may be attributed to the Fe^(3+)-doping and possible Mn ions scattering to electrons. The Fe^(3+) doping may lead to the formation of Fe^(3+)-O^(2-)-Mn^(4+) channels, which could terminate the double exchange Mn^(3+)-O^(2-)-Mn^(4+) channels. The antiferromagnetic clusters of Fe ions may induce the Mn ions to scetter to the electrons.展开更多
The effects of Al ion doping on the Mn site were studied for the colossal magnetoresistance material La_(0.67)Ca_(0.33)MnO_3. It is found that the volume of the crystal cell decreases monotonically when the population...The effects of Al ion doping on the Mn site were studied for the colossal magnetoresistance material La_(0.67)Ca_(0.33)MnO_3. It is found that the volume of the crystal cell decreases monotonically when the population of Al^(3+) increases across the entire doping range. As the Al^(3+) population increases, the resistance of the material rises rapidly, while the insulator-metal transition temperature T_(IM) decreases linearly. At small Al^(3+) dosage, a thermal activation model properly describes the transport properties at T>T_(IM), while a metallic model is more suitable at T<T_(IM). The variation of transport properties with the change of Al dosage may be attributed to lattice distortion caused by the destruction of Mn^(3+)-O^(2-)-Mn^(4+) double exchange channel as a result of Al^(3+)-doping. The doped Al^(3+) ions may modify the local field for electrons so to affect the transport properties.展开更多
Systematic studies of the transport properties of La0.67Ca0.33Mn1-xFexO3 (x=0-0.3) systems showed that with increasing Fe-doping content x the resistance increases and the insulator-metal transition temperature moves ...Systematic studies of the transport properties of La0.67Ca0.33Mn1-xFexO3 (x=0-0.3) systems showed that with increasing Fe-doping content x the resistance increases and the insulator-metal transition temperature moves to lower temperature. For small doping content, the transport property satisfies metal transport behavior below the transition temperature, and above the transition temperature it satisfies the small polaron model. This behavior can be explained by Fe^3+ doping, which easily forms Fe^3+ -O^2- -Mn^4+ channel, suppressing the double exchange Mn^3+ -O^2- -Mn^4+ channel and enhancing the spin scattering of Mn ions induced by antiferromagnetic clusters of Fe ions.展开更多
文摘Y3Al5O12∶Eu nanophosphors were synthesized by a gel combustion method. The structure of phosphors was characterized by XRD and FTIR. YAG phase came to occur when YAG∶Eu precursors were sintered at 800 ℃, although the phase was mainly amorphous. The organic groups pyrolyzed completely and pure YAG phase was obtained in the samples sintered at 900 ℃. In the formation of YAG phase, no intermediate phases such as YAP and YAM were detected. Both 5D0 → 7F1 orange and 5D0 → 7F2 red emission could be observed for all the sintered samples. However, the emission of amorphous samples was greatly different from that of crystalline ones. The former was mainly 5D0 → 7F2 red emission, but the latter was 5D0 → 7F1 orange emission. As sintering temperature rises, the ratio of orange to red for phosphors increases. Eu could be doped up to 8% in YAG host lattice, and fluorescence quenching was absent. It indicated that the gel combustion synthesis method can increase emission intensity and quenching concentration due to a good distribution of Eu3+ activators in Y3Al5O12 matrix.
文摘The transport properties were studied for rare earth manganese oxide La_(0.67)Ca_(0.33)Mn_(1-x)Fe_xO_3 (x=0～0.3) systems. It is found that with increasing Fe^(3+)-doping content x, the resistance increases and the insulator-metal transition temperature (T_(IM)) shifts to lower temperature. If the doping content is small, the transport properties manifest metallic characteristics in the temperature range of T<T_(IM), while they will obey a thermal activation model in the temperature range of T>T_(IM). Such a behavior may be attributed to the Fe^(3+)-doping and possible Mn ions scattering to electrons. The Fe^(3+) doping may lead to the formation of Fe^(3+)-O^(2-)-Mn^(4+) channels, which could terminate the double exchange Mn^(3+)-O^(2-)-Mn^(4+) channels. The antiferromagnetic clusters of Fe ions may induce the Mn ions to scetter to the electrons.
文摘The effects of Al ion doping on the Mn site were studied for the colossal magnetoresistance material La_(0.67)Ca_(0.33)MnO_3. It is found that the volume of the crystal cell decreases monotonically when the population of Al^(3+) increases across the entire doping range. As the Al^(3+) population increases, the resistance of the material rises rapidly, while the insulator-metal transition temperature T_(IM) decreases linearly. At small Al^(3+) dosage, a thermal activation model properly describes the transport properties at T>T_(IM), while a metallic model is more suitable at T<T_(IM). The variation of transport properties with the change of Al dosage may be attributed to lattice distortion caused by the destruction of Mn^(3+)-O^(2-)-Mn^(4+) double exchange channel as a result of Al^(3+)-doping. The doped Al^(3+) ions may modify the local field for electrons so to affect the transport properties.
基金Project supported by the National Natural Science Foundation ofChina (No. 10274049) Foundation of the Natural Science of Zhe-jiang Province (Nos. RC015056 and 502122) Science & Tech-nology Development Foundation of the Education Committee of Sh-anghai Municipality (No. 02AK42)and the Shanghai LeadingAcademic Discipline Program (No. 01A16)
文摘Systematic studies of the transport properties of La0.67Ca0.33Mn1-xFexO3 (x=0-0.3) systems showed that with increasing Fe-doping content x the resistance increases and the insulator-metal transition temperature moves to lower temperature. For small doping content, the transport property satisfies metal transport behavior below the transition temperature, and above the transition temperature it satisfies the small polaron model. This behavior can be explained by Fe^3+ doping, which easily forms Fe^3+ -O^2- -Mn^4+ channel, suppressing the double exchange Mn^3+ -O^2- -Mn^4+ channel and enhancing the spin scattering of Mn ions induced by antiferromagnetic clusters of Fe ions.
