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1,076 results on '"Li, Ji-Guang"'

16. Probing Multiple Electric Dipole Forbidden Optical Transitions in Highly Charged Nickel Ions

Author

Liang, Shi-Yong, Zhang, Ting-Xian, Guan, Hua, Lu, Qi-Feng, Xiao, Jun, Chen, Shao-Long, Huang, Yao, Zhang, Yong-Hui, Li, Cheng-Bin, Zou, Ya-Ming, Li, Ji-Guang, Yan, Zong-Chao, Derevianko, Andrei, Zhan, Ming-Sheng, Shi, Ting-Yun, and Gao, Ke-Lin

Subjects
Physics - Atomic Physics
Abstract

Highly charged ions (HCIs) are promising candidates for the next generation of atomic clocks, owing to their tightly bound electron cloud, which significantly suppresses the common environmental disturbances to the quantum oscillator. Here we propose and pursue an experimental strategy that, while focusing on various HCIs of a single atomic element, keeps the number of candidate clock transitions as large as possible. Following this strategy, we identify four adjacent charge states of nickel HCIs that offer as many as six optical transitions. Experimentally, we demonstrated the essential capability of producing these ions in the low-energy compact Shanghai-Wuhan Electron Beam Ion Trap. We measured the wavelengths of four magnetic-dipole ($M$1) and one electric-quadrupole ($E$2) clock transitions with an accuracy of several ppm with a novel calibration method; two of these lines were observed and characterized for the first time in controlled laboratory settings. Compared to the earlier determinations, our measurements improved wavelength accuracy by an order of magnitude. Such measurements are crucial for constraining the range of laser wavelengths for finding the "needle in a haystack" narrow lines. In addition, we calculated frequencies and quality factors, evaluated sensitivity of these six transitions to the hypothetical variation of the electromagnetic fine structure constant $\alpha$ needed for fundamental physics applications. We argue that all the six transitions in nickel HCIs offer intrinsic immunity to all common perturbations of quantum oscillators, and one of them has the projected fractional frequency uncertainty down to the remarkable level of 10$^{-19}$., Comment: To be published in Physical Review A

Published
2021
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44. Grafting Carbon Dots on Persistent Luminescence Phosphors to Generate Remarkably Improved NIR Afterglow for Microenvironment Fluorescence Detection.

Author

Xiahou, Junqing, Cao, Li, Huang, Sai, Zhang, Tao, Li, Ji‐Guang, and Zhu, Qi

Subjects
LUMINESCENCE, PHOSPHORS, FLUORESCENCE, ENERGY transfer, FLUORESCENT dyes, ELECTRON traps
Abstract

Recently, combining long afterglow materials with organic fluorescent dyes, particularly carbon dots (CDs) to produce heterojunction and improve its luminescence and persistence properties became an important research direction. However, the precise role of these internal defects in the energy transfer process of CD@inorganic matrix composite fluorescent materials has not been thoroughly discussed. Establishing matching trap level to promote the energy transfer between the trap level and CDs level not only helps to enhance the afterglow performance, but also can explain the heterogeneous structure interaction between organic–inorganic fluorescent materials. Herein, ZLAGC@CDs luminescent composite is successfully synthesized via coating CDs on Zn1‐x(Li/Al)xGa2xO4:0.005Cr3+ (ZLAGC, x = 0–1), which exhibits a unique double emission at ≈430 nm (the defect luminescence of CDs) and 718 nm (the 2E→4A2 transition of Cr3+). After coating, the energy transfer from the defect level of CDs to the excited state of Cr3+ enhanced the NIR emission. The electron transfer between the defect level of CDs and the split deeper trap level of ZLAGC also improved the visible and near‐infrared (NIR) afterglow. The fluorescence and afterglow signals of ZLAGC@CDs are highly sensitive to solution pH under acidic conditions, indicating that the prepared fluorescent composite has potential application in acid microenvironment fluorescence detection. [ABSTRACT FROM AUTHOR]

Published
2024
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45. Effect of ball milling time on microstructure and mechanical properties of ultrafine- grained Mg-3Al-Zn alloy prepared by powder metallurgy

Author

FANG Wa, LI Ji-guang, and DU Zheng-yong

Subjects
ultra-fine grain, magnesium alloy, microstructure, mechanical property, ball milling time, Materials of engineering and construction. Mechanics of materials, TA401-492
Abstract

The ultrafine-grained Mg-3Al-Zn alloy was prepared by high energy ball milling,cold vacuum press and warm extrusion. The influence of ball milling time on the microstructure and mechanical properties of the alloy was studied. The results show that Al and Zn elements completely dissolve into the magnesium matrix in the process of ball milling. The single phase solid solution is formed. After the ball-milling for 20 h, the average particle size of the powder particles is about 25 μm, and the average grain size is about 45 nm. After the powder is densified by cold pressing and warm extruded, the average grain size of the alloy milled for 20 h is 600 nm, and the grain shape is regular and equiaxed crystal. All ultrafine-grained alloys show higher mechanical properties. The yield strength, tensile strength and breaking strain of the alloy after ball milling for 20 h are 369 MPa, 401 MPa and 3.5%, respectively. The tensile true stress-true strain curve of ultrafine-grained magnesium alloy shows a characteristic of ideal rigid plasticity. The compression true stress-true strain curve can be divided into three stages: working hardening, working softening and working hardening.

Published
2020
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