We report on the first dark-matter(DM)search results from PandaX-I,a low threshold dual-phase xenon experiment operating at the China JinPing Underground Laboratory.In the 37-kg liquid xenon target with 17.4 live-days...We report on the first dark-matter(DM)search results from PandaX-I,a low threshold dual-phase xenon experiment operating at the China JinPing Underground Laboratory.In the 37-kg liquid xenon target with 17.4 live-days of exposure,no DM particle candidate event was found.This result sets a stringent limit for low-mass DM particles and disfavors the interpretation of previously-reported positive experimental results.The minimum upper limit,3.7×10-44cm2,for the spin-independent isoscalar DM-particle-nucleon scattering cross section is obtained at a DM-particle mass of 49 GeV/c2at 90%confidence level.展开更多
1.5at% Eu-doped GaN powders were prepared by a co-precipitation method.Powder X-ray diffraction(XRD)results shows that there is only the wurtzite phase.Cathodoluminescence spectra were measured at room temperature and...1.5at% Eu-doped GaN powders were prepared by a co-precipitation method.Powder X-ray diffraction(XRD)results shows that there is only the wurtzite phase.Cathodoluminescence spectra were measured at room temperature and liquid nitrogen temperature,respectively.The band-to-band luminescence of GaN was shifted from 373 nm to 368 nm with the temperature decreasing from room temperature to liquid nitrogen temperature.The luminescence peaks at 537,557,579,590,597,614,653 and 701 nm are attributed to the Eu ions related transitions in the host of GaN powders and the peak positions were not influenced by the variation of temperature.With the increase of accelerating voltage,the intensity of all luminescence peaks was increased.The strongest luminescence peak at 614 nm shows non-symmetrical shape and is composed of 612,615 and 621 nm through Lorentzian fitting,which indicates there are oxygen and nitrogen environments of the Eu3+ions in the Eu-doped GaN powders.展开更多
Eu-doped GaN was prepared by solid-state reaction with Ga_2O_3,Eu_2O_3 and NH_3 applied as raw materials.The structural and optical properties were investigated.According to XRD results,wurtzite-type GaN powder withou...Eu-doped GaN was prepared by solid-state reaction with Ga_2O_3,Eu_2O_3 and NH_3 applied as raw materials.The structural and optical properties were investigated.According to XRD results,wurtzite-type GaN powder without Eu_2O_3phase was obtained at 1000℃ and the grain size was about 20 run.Compared to the undoped GaN powder,all the Raman peaks of Eu-doped GaN powder were shifted towards lower phonon frequency about 2-6 cm^(-1),which may be resulted from the strain caused by the Eu^(3+) doping.The cathodo-luminescence(CL) spectra were measured from 80 to 293 K.Ultraviolet luminescence and Eu^(3+) luminescence were both observed when the temperature was below 200 K.When the temperature was increased to 293 K,the ultraviolet luminescence disappeared.However,the intensity of Eu^(3+) luminescence was nearly not influenced by temperature.A donor-acceptor pair(DAP) model based on O_N and Mg_(Ga) was pointed out for explaining the luminescence mechanism.The cathodo-luminescence spectra of nominal 1.0%,2.0%,3.0%and 5.0%(mole fraction) Eu-doped GaN at room temperature were summarized,which suggestes the 2.0%Eu-doped GaN has the highest Eu luminescent intensity.展开更多
基金supported by the 985-Ⅲ grant from Shanghai Jiao Tong Universitythe National Basic Research Program of China from Ministry of Science and Technology of China (Grant No.2010CB833005)+6 种基金the National Natural Science Foundation of China (Grant No.11055003)the Office of Science and Technology in Shanghai Municipal Government (Grant No.11DZ2260700)support from China Postdoctoral Science Foundation (Grant No.2014M551395)sponsored by Shandong UniversityPeking Universitythe University of Marylandthe University of Michigan
文摘We report on the first dark-matter(DM)search results from PandaX-I,a low threshold dual-phase xenon experiment operating at the China JinPing Underground Laboratory.In the 37-kg liquid xenon target with 17.4 live-days of exposure,no DM particle candidate event was found.This result sets a stringent limit for low-mass DM particles and disfavors the interpretation of previously-reported positive experimental results.The minimum upper limit,3.7×10-44cm2,for the spin-independent isoscalar DM-particle-nucleon scattering cross section is obtained at a DM-particle mass of 49 GeV/c2at 90%confidence level.
基金supported by the National Natural Science Foundation of China(Grant Nos.51002179 and 61306004)the Natural Science Fund of Jiangsu Province(Grant No.BK20130263)the Instruments Function Innovation of Chinese Academy of Sciences(Grant No.yg2012093)
文摘1.5at% Eu-doped GaN powders were prepared by a co-precipitation method.Powder X-ray diffraction(XRD)results shows that there is only the wurtzite phase.Cathodoluminescence spectra were measured at room temperature and liquid nitrogen temperature,respectively.The band-to-band luminescence of GaN was shifted from 373 nm to 368 nm with the temperature decreasing from room temperature to liquid nitrogen temperature.The luminescence peaks at 537,557,579,590,597,614,653 and 701 nm are attributed to the Eu ions related transitions in the host of GaN powders and the peak positions were not influenced by the variation of temperature.With the increase of accelerating voltage,the intensity of all luminescence peaks was increased.The strongest luminescence peak at 614 nm shows non-symmetrical shape and is composed of 612,615 and 621 nm through Lorentzian fitting,which indicates there are oxygen and nitrogen environments of the Eu3+ions in the Eu-doped GaN powders.
基金partly supported by the National Natural Science Foundation of China(NSFC)(61306004,51002179,11247023,51272270)the Natural Science Foundation of Jiangsu Province of China(BK20130263)+3 种基金the Functional Development Program of the Chinese Academy of Sciences(yg2012093)Collaborative Innovation Center of Suzhou Nano Science and Technologythe PAPD and USTS Cooperative Innovation CenterPostgraduate innovation and educational reform project of Suzhou University of Science and Technology(091420058)
文摘Eu-doped GaN was prepared by solid-state reaction with Ga_2O_3,Eu_2O_3 and NH_3 applied as raw materials.The structural and optical properties were investigated.According to XRD results,wurtzite-type GaN powder without Eu_2O_3phase was obtained at 1000℃ and the grain size was about 20 run.Compared to the undoped GaN powder,all the Raman peaks of Eu-doped GaN powder were shifted towards lower phonon frequency about 2-6 cm^(-1),which may be resulted from the strain caused by the Eu^(3+) doping.The cathodo-luminescence(CL) spectra were measured from 80 to 293 K.Ultraviolet luminescence and Eu^(3+) luminescence were both observed when the temperature was below 200 K.When the temperature was increased to 293 K,the ultraviolet luminescence disappeared.However,the intensity of Eu^(3+) luminescence was nearly not influenced by temperature.A donor-acceptor pair(DAP) model based on O_N and Mg_(Ga) was pointed out for explaining the luminescence mechanism.The cathodo-luminescence spectra of nominal 1.0%,2.0%,3.0%and 5.0%(mole fraction) Eu-doped GaN at room temperature were summarized,which suggestes the 2.0%Eu-doped GaN has the highest Eu luminescent intensity.
