Rare earth Sm3＋, Pr3＋doped NaSr2（NbO3）5 red phosphors were successfully synthesized. X-ray diffraction analysis indi-cated that all the samples were single phased. The luminescence property was investigated in det...Rare earth Sm3＋, Pr3＋doped NaSr2（NbO3）5 red phosphors were successfully synthesized. X-ray diffraction analysis indi-cated that all the samples were single phased. The luminescence property was investigated in detail by diffuse-reflectance spectra and photoluminescence spectra measurement. Both NaSr2（NbO3）5：Sm3＋and NaSr2（NbO3）5：Pr3＋phosphors showed strong absorption in near ultraviolet region, which was suitable for application in LEDs. When excited by UV light, they both emitted bright red emission with CIE chromaticity coordinates （0.603, 0.397） and （0.669, 0.330）, respectively. The optimal doping concentration of Sm3＋doped NaSr2（NbO3）5 was measured to be 0.04 and that for Pr3＋doped NaSr2（NbO3）5 was 0.01. The integral emission intensity was also measured and compared with the commercial red phosphor Y2O3：Eu3＋. The results indicated that NaSr2（NbO3）5：RE3＋（RE=Sm, Pr） have potential to serve as a red phosphor for UV pumped white LEDs.展开更多
The thermoluminescence （TL） properties of Ce3＋ doped NaSr4（BO3）3 phosphor under the β-ray irradiation were reported. The polycrystalline sample was synthesized by high temperature solid-state reaction. The TL gl...The thermoluminescence （TL） properties of Ce3＋ doped NaSr4（BO3）3 phosphor under the β-ray irradiation were reported. The polycrystalline sample was synthesized by high temperature solid-state reaction. The TL glow curve of NaSr4（BO3）3：Ce3＋ phosphor was composed of only one peak. TL kinetic parameters of NaSr4（BO3）3：Ce3＋ were deduced by the peak shape method, the activation energy （E） was 0.590 eV and the frequency factor was 1.008×10^6S^-1. TL dose response was linear in the range of measurement. The 3-dimensional （3D） TL emission spectrum was also recorded, the emission spectrum consisted of two bands located at 441 and 479 nm respectively, corresponding to the characteristic 4f^05d^1→2F（5/2,7/2） transitions of the Ce3＋ ion. The fading behavior of the NaSr4（BO3）3：Ce3＋ phosphor over a period of 15 d was also studied.展开更多
Background The search of heavy atoms is crucial to the de novo determination of protein structures.Typically,the difference Patterson map is calculated as a first step to solve substructure.However,the pseudo-peaks an...Background The search of heavy atoms is crucial to the de novo determination of protein structures.Typically,the difference Patterson map is calculated as a first step to solve substructure.However,the pseudo-peaks and noises inherent in such maps arising from the high symmetry and large size of protein structures accompanied with the data collection errors inevitably pose a challenge in accurate real space-based substructure determination.Purpose In order to mitigate such pseudo-peaks and noises and further improve signal-to-noise ratio(SNR)of the difference Patterson map,the noise and artifact suppression using resampling(NASR)method originally proposed in nuclear magnetic resonance is introduced into protein crystallography in this work to optimize the difference Patterson map.Methods The NASR method makes use of the statistical learning theory,which in this work repeatedly samples a fixed portion of diffraction data(sub-dataset)randomly followed by a statistical analysis of the multiple calculated difference Patterson maps to discard pseudo-peaks and noises.Its feasibility is based on the fact that the true vector peaks of the heavy atoms keep static in the multiple random sub-datasets,whereas the pseudo-peaks and noises fluctuate remarkably.And the key of this method lies in the design of a weighting function to distinguish true vector peaks from pseudo-peaks and noises,as well as a proper selection of the parameters associated with the function.Results The introduced NASR method is both numerically and experimentally demonstrated to be feasible in suppressing spurious peaks and non-correlative noises intrinsic to the difference Patterson maps.As a result,the SNR of the difference Patterson maps can be enhanced to some extent to facilitate real space-based substructure determination.Conclusion It is therefore anticipated that the proposed method may provide a meaningful insight into how to denoise the difference Patterson maps,which in turn assists in locating heavy atoms and further facilitates de novo protein structure determination.展开更多
基金supported by National Science Foundation for Distinguished Young Scholars(50925206)Specialized Research Fund for the Doctoral Program of Higher Education(20120211130003)
文摘Rare earth Sm3＋, Pr3＋doped NaSr2（NbO3）5 red phosphors were successfully synthesized. X-ray diffraction analysis indi-cated that all the samples were single phased. The luminescence property was investigated in detail by diffuse-reflectance spectra and photoluminescence spectra measurement. Both NaSr2（NbO3）5：Sm3＋and NaSr2（NbO3）5：Pr3＋phosphors showed strong absorption in near ultraviolet region, which was suitable for application in LEDs. When excited by UV light, they both emitted bright red emission with CIE chromaticity coordinates （0.603, 0.397） and （0.669, 0.330）, respectively. The optimal doping concentration of Sm3＋doped NaSr2（NbO3）5 was measured to be 0.04 and that for Pr3＋doped NaSr2（NbO3）5 was 0.01. The integral emission intensity was also measured and compared with the commercial red phosphor Y2O3：Eu3＋. The results indicated that NaSr2（NbO3）5：RE3＋（RE=Sm, Pr） have potential to serve as a red phosphor for UV pumped white LEDs.
基金supported by the National Key Project of Basic Research of China (G1998061312)
文摘The thermoluminescence （TL） properties of Ce3＋ doped NaSr4（BO3）3 phosphor under the β-ray irradiation were reported. The polycrystalline sample was synthesized by high temperature solid-state reaction. The TL glow curve of NaSr4（BO3）3：Ce3＋ phosphor was composed of only one peak. TL kinetic parameters of NaSr4（BO3）3：Ce3＋ were deduced by the peak shape method, the activation energy （E） was 0.590 eV and the frequency factor was 1.008×10^6S^-1. TL dose response was linear in the range of measurement. The 3-dimensional （3D） TL emission spectrum was also recorded, the emission spectrum consisted of two bands located at 441 and 479 nm respectively, corresponding to the characteristic 4f^05d^1→2F（5/2,7/2） transitions of the Ce3＋ ion. The fading behavior of the NaSr4（BO3）3：Ce3＋ phosphor over a period of 15 d was also studied.
基金the National Natural Science Foundation of China(31570744).
文摘Background The search of heavy atoms is crucial to the de novo determination of protein structures.Typically,the difference Patterson map is calculated as a first step to solve substructure.However,the pseudo-peaks and noises inherent in such maps arising from the high symmetry and large size of protein structures accompanied with the data collection errors inevitably pose a challenge in accurate real space-based substructure determination.Purpose In order to mitigate such pseudo-peaks and noises and further improve signal-to-noise ratio(SNR)of the difference Patterson map,the noise and artifact suppression using resampling(NASR)method originally proposed in nuclear magnetic resonance is introduced into protein crystallography in this work to optimize the difference Patterson map.Methods The NASR method makes use of the statistical learning theory,which in this work repeatedly samples a fixed portion of diffraction data(sub-dataset)randomly followed by a statistical analysis of the multiple calculated difference Patterson maps to discard pseudo-peaks and noises.Its feasibility is based on the fact that the true vector peaks of the heavy atoms keep static in the multiple random sub-datasets,whereas the pseudo-peaks and noises fluctuate remarkably.And the key of this method lies in the design of a weighting function to distinguish true vector peaks from pseudo-peaks and noises,as well as a proper selection of the parameters associated with the function.Results The introduced NASR method is both numerically and experimentally demonstrated to be feasible in suppressing spurious peaks and non-correlative noises intrinsic to the difference Patterson maps.As a result,the SNR of the difference Patterson maps can be enhanced to some extent to facilitate real space-based substructure determination.Conclusion It is therefore anticipated that the proposed method may provide a meaningful insight into how to denoise the difference Patterson maps,which in turn assists in locating heavy atoms and further facilitates de novo protein structure determination.
