Y4.67Si3O13-based phosphors: Structure,morphology and upconversion luminescence for optical thermometry

How to improve the sensitivity of the temperature-sensing luminescent materials is one of the most important objects currently. In this work, to obtain high sensitivity and learn the corresponding mechanism, the rare earth (RE) ions doped Y_4.67Si₃O₁₃ (YS) phosphors were developed by solid-state reaction. The phase purity, structure, morphology and luminescence characteristics were evaluated by XRD, TEM, emission spectra, etc. The change of the optical bandgaps between the host and RE-doped phosphors was found, agreeing with the calculation results based on density-functional theory. The temperature-dependence of the upconversion (UC) luminescence revealed that a linear relationship exists between the fluorescence intensity ratio of Ho³⁺ and temperature. The theoretical resolution was evaluated. High absolute (0.083 K⁻¹) and relative (3.53% K⁻¹ at 293 K) sensitivities have been gained in the YS:1%Ho³⁺, 10%Yb³⁺. The effect of the Yb³⁺ doping concentration and pump power on the sensitivities was discussed. The pump-power–dependence of the UC luminescence indicated the main mechanism for high sensitivities in the YS:1%Ho³⁺, 10%Yb³⁺. Moreover, the decay-lifetime based temperature sensing was also evaluated. The above results imply that the present phosphors could be promising candidates for temperature sensors, and the proposed strategies are instructive in exploring other new temperature sensing luminescent materials.     

Electrochemical tuning induced oxygen vacancies for the photoluminescence enhancement

Oxygen vacancies(OVs) can greatly influence the properties of luminescent materials, however, finding a facile way of controlling the specific defect remains challenging. The traditional methods usually require either high temperature or long period of time. Here, we demonstrate an electrochemical strategy to implant OVs in as serious of oxides including Li₂GeZnO₄(LZGO), Li₂GeZnO₄:Mn²⁺(LZGO:Mn) and LiGa₅O₈:Cr³⁺(LGO:Cr). The photoluminescence intensity of all these oxides is increased by 43%, 36% and 38% respectively. Our electrochemical strategy not only exhibits facile advantage in tuning the OVs in the lattice of luminescent material, but also provides a method with general efficacy which should be benificial for many other correlated applications.     

Photoluminescence and temperature sensing of lanthanide Eu3+ and transition metal Mn4+ dual-doped antimoniate phosphor through site-beneficial occupation

For a long time, rare-earth ion-doped phosphors have been widely used in temperature sensing because of their excellent light-emitting properties. However, most of the rare earth elements are relatively rare and expensive, so the transition group elements that are economical and easy to obtain have been favored by researchers. This paper presents a new type of phosphor doped with rare earth ion and transition metal for optical temperature measurement. In recent years, Mn⁴⁺-doped phosphors have attracted wide attention because of their strong deep red light-emitting properties. La₂LiSbO₆ provides a good host environment for Mn⁴⁺ and Eu³⁺ due to its unique crystal structure. In this paper, a series of La₂LiSbO₆ phosphors singly doped with Mn⁴⁺ and Eu³⁺, and co-doped with Eu³⁺/Mn⁴⁺ were synthesized. The crystal phases and optical properties of these materials were characterized and analyzed in detail. We specifically studied the temperature dependence of the fluorescence intensity of the optimized La₂LiSbO₆: Eu³⁺, Mn⁴⁺ phosphors at 303K–523K. The experimental results prove that the thermal responses of Mn⁴⁺ and Eu³⁺ are different. With increasing temperature, the thermal quenching of the Mn⁴⁺ fluorescence intensity is much faster than that of Eu³⁺, so the temperature characteristics can be explored by the fluorescence intensity ratio (FIR) of Eu³⁺ to Mn⁴⁺. At 523 K, its maximum relative sensitivity and maximum absolute sensitivity can reach 0.891% K⁻¹ and 0.000264 K^-1, respectively. Our experimental analysis shows that La₂LiSbO₆:Eu³⁺/Mn⁴⁺ phosphors have relatively high temperature sensitivity and have potential application prospects in the field of high temperature sensing.     

An efficient polymer solar cell using graphene oxide interface assembled via layer-by-layer deposition

Graphene oxide (GO) is widely used as an interfacial material in applications such as organic light emitting diodes and photovoltaic devices. Herein we report a layer-by-layer (LbL) assembled GO thin film as an anode interfacial layer (AIL) for efficient polymer solar cells (PSCs). The GO thin film is fabricated by alternately depositing cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA) and GO on ITO/glass substrate, which possesses controllable thickness by adjusting LbL deposition frequency. The presence of ultrathin GO films improves the work function of ITO, leading to a better contact between the active layer and ITO anode. With the optimized number of deposition times, the efficiency of 6.04% for the PSC with PDDA-GO bilayer (GO-2) as the AIL was achieved.     

Fabrication of 1D long chain-like metal porphyrin-based coordination complexes for high-efficiency hydrogen evolution and photoelectric response

Hydrogen production from electrocatalytic water splitting has aroused extensive attention in many fields recently. Fabrication of low-cost and high-efficiency electrocatalysts are still an urgent and challenging work. Porphyrins as visible-light photosensitizers have been extensively utilized in visible-light photocatalysts and photoelectronic materials. So, fabrication of novel porphyrin-based complexes will be benefited for high-efficiency hydrogen evolution and photoelectric response. Here a series of zirconium porphyrin-based coordination complexes were successfully fabricated via a facile two-step strategy. Due to the unique long chain-like structure and low charge-transfer resistance, the zirconium porphyrin-based coordination complexes displayed excellent electrocatalytic performance for hydrogen evolution reaction. The ZrTPP-PTA-1 showed a low overpotential of 60 mV at the current density 10 mA cm⁻² and a Tafel slope of 87 mV dec⁻¹ with an ultralow electron transfer resistance of 17.5 Ω. In addition, a quick photocurrent response occurred for these coordination complexes with a visible-light illumination. The photocurrent of the ZrTPP-OA-2 rised up to 2.5 μA under visible-light irradiation. With this pleasant result, these zirconium porphyrin-based coordination complexes have a great potential to become available alternative of current noble electrocatalysts for photoelectric application.     

多因素条件下单级齿轮系统的非线性特性

考虑啮合刚度、齿侧间隙和轴承支撑间隙等因素,运用集中质量法建立了三自由度直齿圆柱齿轮副弯扭耦合非线性振动模型,并据此研究了各参数对齿轮系统非线性振动特性的影响。结果表明：齿侧间隙一定时,随着频率的升高,系统由周期运动通过激变直接进入混沌,然后又由混沌通过激变变为周期运动;在周期运动中,系统经过倍周期分岔,由双周期运动变为四周期运动,然后又通过逆倍周期分岔,由四周期运动变为双周期运动,之后又由双周期运动变为单周期运动;不同的输入转频条件下,间隙变化使系统表现出不同分岔特性,在某些特定频率下,间隙变化只增加系统响应能量变化,并不改变其动力学特性。     

Kinematic calibration of a 3-P(Pa)S parallel-type spindle head considering the thermal error

Calibration is considered to be the most effective way to improve the accuracy of parallel kinematic machine tools (PKMTs). However, ordinary calibrations only considered the time-invariant errors (manufacturing error), neglecting some time-variant errors, a significant one of which is thermal error. Therefore, in this paper, the influence of thermal error was considered in the calibration of a 3-P(Pa)S parallel-type spindle head. First, a new kinematic model of the spindle head was proposed, which is closer to the real physical model, so the thermal error of the spindle head can be considered in the model. Second, the structural parameters of the spindle head were expressed as the sum of the ideal parameters, the manufacturing errors, and the thermal errors. Third, the pose (position and orientation) of the end effector and the temperature of the spindle head were measured. The positions of the temperature sensors were selected using the global temperature sensitivity index (GTSI), which is derived from the global sensitivity index (GSI). Thus, by setting a standard temperature, the thermal error of the structural parameter can be obtained. Fourth, the influence of the thermal error was inputted into the identification equation for calibration, so the results are the structural parameters at the standard temperature (20 °C). To solve the ill-conditioning problem, a Regularization method was used in the identification. Finally, the calibration was verified on a 3-P(Pa)S-XY machine tool. The RTCP test, performed immediately after the measurement, shows that the maximum position error after the calibration is 0.019 mm at the tilt angle of 30° and 0.037 mm at 20°. In addition, the RTCP test after a temperature change shows that the calibration considering the thermal error can improve the average position accuracy from 0.025 mm to 0.015 mm. The calibration method in this paper is expected to be applicable for other machine tools.     

Alcohol-assisted rapid growth of vertically aligned carbon nanotube arrays

Millimeter-to-centimeter scale vertically aligned carbon nanotube (VACNT) arrays are widely studied because of their immense potential in a range of applications. Catalyst control during chemical vapor deposition (CVD) is key to maintain the sustained growth of VACNT arrays. Herein, we achieved ultrafast growth of VACNT arrays using Fe/Al₂O₃ catalysts by ethanol-assisted two-zone CVD. One zone was set at temperatures above 850 °C to pyrolyze the carbon source and the other zone was set at 760 °C for VACNT deposition. By tuning synthesis parameters, up to 7 mm long VACNT arrays could be grown within 45 min, with a maximal growth rate of ∼280 μm/min. Our study indicates that the introduction of alcohol vapor and separation of growth zones from the carbon decomposition zone help reduce catalyst particle deactivation and accelerate the carbon source pyrolysis, leading to the promotion of VACNT array growth. We also observed that the catalyst film thickness did not significantly affect the CNT growth rate and microstructures under the conditions of our study. Additionally, the ultralong CNTs showed better processability with less structural deformation when exposed to solvent and polymer solutions. Our results demonstrate significant progress towards commercial production and application of VACNT arrays.     

一种新型光伏阵列在线故障检测方法研究

太阳能光伏电站是国内外重点发展的绿色能源装备。光伏阵列是光伏电站的核心部件。目前光伏阵列的故障检测多采用线下人工排查法,无法实现实时在线监控及有效的故障报警。为此,提出了一种新型光伏阵列故障在线检测法。在新型检测法中,提出了电压电流检测初筛法及电池组件参数估算法。电压电流检测可以实现故障组件被定位在小范围内,而电池组件参数估算法则可以根据光伏组件的光照强度和温度估算出光伏组件的性能参数,进而准确定位故障组件。经实验验证表明,新型光伏阵列故障在线检测法及其监控仪器的故障判别准确性在90%以上。     

Tool point dynamics prediction by a three-component model utilizing distributed joint interfaces

In machine dynamics the tool point frequency response functions (FRFs) are employed to predict the stable machining conditions. In this paper, a combined analytical–experimental substructuring procedure is proposed to determine the tool point FRFs for different holder–tool configurations. The method employs the measured spindle-machine FRFs and analytical models of the tool and the holder to predict the tool tip FRFs for different sets of tools and holders mounted on the machine spindle without the need for repeated experimental measurements. Distributed joint interfaces are used to couple the three-component model of the machine. The machine tool tip FRFs with different tool–holder combinations are obtained assuming the clamping conditions at joint interfaces remain unchanged. An experimental case study is provided to demonstrate the applicability of the proposed method in dynamic modeling of machine tool.