Realizing highly efficient multicolor tunable emissions from Tb³⁺ and Eu³⁺ co-doped CaGd₂(WO₄)₄ phosphors via energy transfer by single ultraviolet excitation for lighting and display applications

Huang, Xiaoyong,Li, Bin,Du, Peng,Guo, Heng,Cao, Renping,Yu, Jae Su,Wang, Kai,Sun, Xiao Wei Elsevier 2018 Dyes and pigments Vol.151 No.-

<P><B>Abstract</B></P> <P>In this paper, we reported on multicolor emission tuning in Tb<SUP>3+</SUP> and Eu<SUP>3+</SUP> co-doped CaGd<SUB>2</SUB>(WO<SUB>4</SUB>)<SUB>4</SUB> phosphors prepared by a traditional high-temperature solid-state reaction. Upon 380 nm ultraviolet excitation, the emission color of CaGd<SUB>2</SUB>(WO<SUB>4</SUB>)<SUB>4</SUB>:Tb<SUP>3+</SUP>,Eu<SUP>3+</SUP> phosphors can be readily tuned from green to yellow, orange and finally to pure red through varying the concentration ratio of Eu<SUP>3+</SUP> and Tb<SUP>3+</SUP> ions. The energy transfer mechanism from Tb<SUP>3+</SUP> to Eu<SUP>3+</SUP> was systematically investigated by photoluminescence spectra, luminescence decay times, and time-resolved spectra. The internal quantum efficiencies of these phosphors were measured, and their thermal stability was also studied. A prototype white light-emitting diode (LED) device was fabricated by using an ultraviolet chip combined with a blend of blue-emitting BaMgAl<SUB>10</SUB>O<SUB>l7</SUB>:Eu<SUP>2+</SUP> phosphors, green-emitting BaSrSiO<SUB>4</SUB>:Eu<SUP>2+</SUP> phosphors, and red-emitting CaGd<SUB>2</SUB>(WO<SUB>4</SUB>)<SUB>4</SUB>:50%Tb<SUP>3+</SUP>,50%Eu<SUP>3+</SUP> phosphors. All the results indicate that the CaGd<SUB>2</SUB>(WO<SUB>4</SUB>)<SUB>4</SUB>:Tb<SUP>3+</SUP>,Eu<SUP>3+</SUP> has great potential application in lighting and displays.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CaGd<SUB>2</SUB>(WO<SUB>4</SUB>)<SUB>4</SUB>:Tb<SUP>3+</SUP>,Eu<SUP>3+</SUP> showed efficient energy-transfer from Tb<SUP>3+</SUP> to Eu<SUP>3+</SUP>. </LI> <LI> CaGd<SUB>2</SUB>(WO<SUB>4</SUB>)<SUB>4</SUB>:Tb<SUP>3+</SUP>,Eu<SUP>3+</SUP> exhibited tunable color emission under 380 nm excitation. </LI> <LI> The energy-transfer mechanism was studied in detail. </LI> <LI> Quantum efficiency and thermal stability were investigated. </LI> <LI> The proof-of-concept LED lamps were fabricated by employing phosphors and UV LEDs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Analysis of elliptical Hertz contact of steel wires of stranded-wire helical spring

Xiaoyong Li,Shilong Wang,Jie Zhou 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.7

A stranded-wire helical spring is formed of a multilayer and coaxial strand of several wires twisted together with the same direction ofspiral. Because of the multilayer structure, the wear on the local area of the steel wires’ surface is related to the elliptical contact betweenadjacent wires during working process. Based on Boussinesq potential functions and elastic half-space model, the contact area and surfacepressure of elliptical Hertz contact were investigated. Moreover, these surface contact quantities are used to expand the calculationof subsurface stress relevant to elliptical contact. It is found that the greater contact angle of two contact wires, the smaller contact areaand greater maximum contact pressure. Meanwhile, the magnitude of subsurface von Mises stress is much higher when the contact angleincreases.

A numerical and effective method for the contact stress calculation of elliptical partial slip

Xiaoyong Li,Liang Liang,Shijing Wu 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.2

A general elliptical Hertzian contact, such as a ball rolling in a non-conforming groove or two non-orthogonal cylinders, is a universalphenomenon in engineering. A partial elliptical contact is formed by contact bodies under a normal force and a transverse force that isinsufficient to cause complete sliding. A computational model based on the semi-analytical method is established to calculate the vonMises stress distribution. Furthermore, a parametric study on factors influencing the location of the maximum von Mises stress point,such as the coefficient of friction and stick zone ratio, is conducted. Results show that the location of the maximum von Mises stresspoint depends on the coefficient of friction f and stick zone ratio c. The von Mises stress increases significantly with the increasing coefficientof friction f. Moreover, the maximum von Mises stress point tends to occur at a subsurface when the stick ratio c increases.

Novel frictional algorithm implementing angular increment for two-dimensional frictional systems

Deng Zhao,Shijing Wu,Qiaoquan Li,Xiaofeng Li,Xiaoyong Li,Xiaosun Wang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.7

This study proposes a new frictional algorithm that implements angular increment. The proposed algorithm is used to solve the numerical solutions of dynamic problems in two-dimensional frictional systems. It can accurately obtain the motion responses of a lumped mass under time-varying external forces, and it can compensate for the shortcomings of the numerical frictional algorithm that implements a time step. Specifically, the proposed algorithm 1) overcomes the difficulties encountered when the angles between resultant tangential forces and slip motion are infinitely close, 2) provides accurate solutions for two-dimensional systems under fierce planar motions, and 3) calculates the responses of the mass within a reasonable period. We compare the computation accuracy, efficiency, and robustness of the proposed frictional algorithm and the previous frictional algorithm [1] through several representative scenarios. We reveal that the proposed algorithm has superior computation accuracy, efficiency, and robustness for two-dimensional frictional problems involving slip/stick transitions and sharp bending.

Resilience-Oriented Performance Assessment Method for Road-Traffic System: A Case Study in Beijing, China

Xiaoyong Ni,Toshihiro Osaragi,Hong Huang,Ruiqi Li,Anying Chen 대한토목학회 2021 KSCE Journal of Civil Engineering Vol.25 No.10

The performance of an urban road-traffic system is affected by many factors, such as the average traffic demand, and the network structure, etc. At the same time, natural disasters, abnormal traffic volume and man-made accidents can result in disturbances which also influence the performance of the system. Resilience of an urban road-traffic system has been an emerging research field. This paper proposes a resilience-oriented performance assessment method based on a traffic flow assignment model to precisely capture the performance of an urban road-traffic system. System functionality is chosen as the key proxy for resilience, which can be calculated based on some index parameters including allocation rate of traffic flow, commuting efficiency on road sections, etc. A case study is implemented in a downtown area in Beijing, China. As to the resilience of the system when faced with huge traffic volume, the results show that the road-traffic system itself has a certain degree of absorption capacity for traffic pressure induced by huge volume. As to the resilience of the system when faced with local network failure, the results show that information dissemination of the network condition and the traffic volume are the key impact factors on system’s resilience curves.

Optimization of Hot Working Parameters of As-Forged Nitinol 60 Shape Memory Alloy Using Processing Maps

Xiaoyong Shu,Shiqiang Lu,Kelu Wang,Guifa Li 대한금속·재료학회 2015 METALS AND MATERIALS International Vol.21 No.4

The hot deformation behavior of as-forged Nitinol 60 alloy (60 wt% Ni, 40 wt% Ti) was studied over the ranges of temperature, 650-850 °C, and strain rate, 0.01-1 s-1, using isothermal constant strain rate compression tests in a Gleeble-3500 simulator. The processing maps, based on the dynamic materials model, were developed to optimize the hot working parameters. The results show that the deformation parameters have a marked effect on the power dissipation efficiency and the instability parameter. A single unstable region (650-775 °C, 0.037-1 s-1), associated with flow localization and/or adiabatic shear, is detected from the processing map. This should be avoided in hot working process. The optimized hot working conditions correspond to 680-790 °C, 0.01- 0.025 s-1 with peak efficiency of 0.45 at 720 °C, 0.01 s-1, and 820-850 °C, 0.1-1 s-1 with peak efficiency of 0.5 at 850 °C, 1 s-1. Microstructure observations indicate that the main deformation mechanism of optimized domains involves dynamic recrystallization.

NOISE MEASURING AND CHARACTERISTICS ANALYSIS OF LIQUID ROCKET ENGINE

LI Feng,LIU Xiaoyong,BAO Futing 한국소음진동공학회 2008 한국소음진동공학회 국제학술대회논문집 Vol.2008 No.7

Design of Layered Aerospace Time Synchronization Architecture and Time Synchronization Links Budget Comparison

Huang Feijiang,Li Xiaoyong,Sun Liping,Sheng wang,Zhang Wenxi,Liu Guangcan 보안공학연구지원센터 2013 International Journal of Future Generation Communi Vol.6 No.6

Analysis and Proofs of Properties in Intransitive Noninterference

Congdong Lv,Xiaoyong Li,Fei Li,Wei Ma 보안공학연구지원센터 2015 International Journal of Hybrid Information Techno Vol.8 No.7

The goal of high assurance systems development by formal verification motivates the investigation of techniques whereby a systems design or implementation can be formally shown to satisfy a formal definition of security. The security of unwinding relations provides a proof method that has been applied to establish that a system satisfies noninterference properties, but it requires significant human ingenuity to define an unwinding relation that forms the basis for the proof, and typically also has involved manual driving (proof rule selection) of the theorem proving tool within which the proof is conducted. The property of purge-based definition proposed by Goguen and Meseguer, intransitive purge-based definition proposed by Haigh and Young, and some more definitions TA-secure, TO-secure, ITO-secure proposed by van der Meyden are considered in this paper. The property can be used in the proof of noninterference property without unwinding relations.

Research on torsional fretting wear behaviors and damage mechanisms of stranded-wire helical spring

Shilong Wang,Xiaoyong Li,Song Lei,Jie Zhou,Yong Yang 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.8

Wear on the local area of steel wires’ surface is attributed to torsional fretting on the working process of stranded-wire helical spring. A mathematical model to calculate normal contact force and angular displacement amplitude among the wires is established first when the spring is impacted. With the experimental parameters obtained from the model, the torsional fretting test, which stimulates torsional fretting among the wires in the working process of the spring, is realized successfully on a newly developed fretting tester. Torsional fretting behaviors are strongly dependent upon normal contact force, angular displacement amplitude, and number of cycles. There are three basic types of T-θ curves (short for torque), angular displacement curves during the process of torsional fretting, namely, parallelogram,elliptic, and linear T-θ curves. To analyze the damage mechanisms, distribution maps of oxygen in the wear scar of spring wires under different working conditions are revealed. The damage gets slight in the partial slip region, mainly with the abrasive wear and the slight oxidative wear, whereas the wear mechanisms are mainly the abrasive wear, the oxidative wear, and the delamination, accompanied with obvious plastic deformation in the mixed fretting and slip regions.