The upconversion luminescences of YAlO3:Er 3+ phosphor co-doping with different Gd 3+ concentrations are investigated under the excitation of 980-and 532-nm diode lasers. A near ultraviolet upconversion emission at 410 nm is observed in YAlO3 under 532-nm excitation. Moreover, the inactive Gd 3+ ions can improve the upconversion intensity efficiently in a certain range of concentration. Under 980-nm excitation, the visible upconversion emissions at 546 and 646 nm are enhanced by about 10 and 8 times at the Gd 3+ concentration of 40%, respectively. The upconversion emission at 410 nm under 532-nm excitation is also enhanced by 7 times. The substitution of Gd 3+ ions for Y 3+ sites changes the local symmetry of Er 3+ , leading to the improvement of upconversion efficiency.OCIS codes: 160.5690, 160.4670, 160.4760. doi: 10.3788/COL201210.081602.In the last several decades, the upconversion luminescence of rare-earth-ion-doped materials has been investigated extensively due to their wide applications in solid-state lasers, flat panel displays, biological labeling, and so on [1−3] . Er 3+ has been reported as one of the most popular and efficient ions for upconversion [4−8] . It can provide several intermediate levels with long life time, which can be directly pumped by several diode lights [9−14] . Recently, upconversion phenomena in Er 3+ -doped YAlO 3 crystals have been widely studied because of their high mechanical hardness and considerable thermal conductivity, among others. Several authors have reported upconversion luminescence in Er 3+ -doped YAlO 3 under 518-, 542.4-, 548.9-, 652.2-, and 980-nm excitations [10,15−17] . Therefore, it is very important to improve their upconversion efficiency. There are many factors affecting the upconversion efficiency, such as the local environment, the dopant concentration, and the distribution of active ions in host materials [18] . A recent study has reported that the luminescence intensity can be enhanced by changing the local environment of luminescent centers, which can be performed by doping some suitable inactive ions in the host. , xGd 3+ (x=0, 0.15, 0.25, 0.4, 0.5, and 0.7) was prepared through a solution combustion synthesis procedure. An aqueous solution containing citric acid, Y(NO 3 ) 3 , Er(NO 3 ) 3 , and Gd(NO 3 ) 3 was used to synthesize the Er 3+ and Gd 3+ co-doped YAlO 3 powders. A citric acid-to-metal nitrate molar ratio of 1.5:1 was employed to prepare the precursor solution. After the combustion, the precursor was calcined at 1 100• C for 2 h. The powders were characterized by X-ray diffraction (XRD) on a Bruker D8 advanced equipment (x) using Cu tube with K α radiation of 0.15406 nm in the 2θ range of 20• -60• . The morphology of the prepared powders was observed by scanning electron microscopy (SEM) using JSM-6610. Upconversion luminescence spectra excited by 980-and 532-nm lasers were obtained in the spectrophotometer (R-500, Japan Spectroscopic Co., Japan). All the measurements were performed at room temperature. Figure 1 shows the representat...

The fault of power circuit breaker (PCB) can lead very serious problems, especially in high voltage-power grid. The structure of contacts may be composed of main contacts and arc contacts, and this structure can avoid ablation of main contacts efficiently. It is necessary to study the eroded state of the arc contacts and the dynamic contact resistance of arc contacts to estimate the operating state of the PCB. The wear of contacts contains arc ablation and mechanical wear through the characteristics of contacts. The arc ablation is caused by the high temperature of the arc and the mechanical wear is caused by the mechanical friction of static and movable contacts. Some experiments have been done under different size of contacts and different current through them. The results show that the mechanical wear increases, sometimes heavier, with the increase of the size of fixed contacts and the decrease of the size of movable ones because the force between fixed and movable contacts becomes larger. The results also show that the ablation of arc contacts increases with the increase of current, especially when the current is up to 20 kA. With the high temperature of arc reaching the hardness point of copper, the arc ablation and mechanical erosion are increasing obviously since the contacts become soft and easy to wear. Another result of the study shows it is important to choose the material of contacts and the force between movable and fixed contacts. The harder and less resistance the material of contacts, the better the operating situation. To monitor the operating situation of the breaker, the dynamic contact resistance was measured 25 times. As a result, the dynamic contact resistance is sensitive to the current and increasing with the increase of continuous experiment time because of the increasing of metal ions. Furthermore, if the SF 6 in the PCB is changes, the dynamic contact resistance would be changed. The dynamic contact resistance in this experiment varies substantially within the range of 80-250 μΩ at the current of 20 kA.

As new energies integrated into grid, the harmonics in the grid are more serious, and the Voltage Detection Active Power Filter (VDAPF) has been used as the mitigation equipment to solve the harmonic problems in power electronic distribution network. The global optimization method generally utilizes 15 min to mitigate harmonic which is named long-time-scale, and it is impossible to mitigate harmonic timely. This paper studies a multi-time-scale harmonic mitigation method which adds 5 min prediction to the global optimization method which is named multi-time-scale. The objective is to correct the deviation of harmonic caused by the long-time-scale harmonic prediction error. This paper utilizes MPC to predict the amplitude and phase variation of the harmonics in short time scale, and utilizes distributed VDAPF to optimize harmonic in long time scale. The IEEE 33 nodes system was used as an example to conduct a comparative analysis of mitigation effects in two different harmonic injection scenarios which injected separately 10 and 20%. The results shows that the mitigating effect of the global optimization method is limited under two different harmonic injection scenarios, and it needs to combine with short time scale harmonic prediction information to ensure the effectiveness and rationality of the mitigation results. When the harmonic current fluctuates, there are unqualified voltage distortion nodes in each region, and the voltage distortion rate is larger. But the MPC can change harmonic prediction in a short time, so every harmonic of each VDAPF conductance values is set bigger, and harmonic conductance of the higher harmonics is relatively lower.

With the use of a large number of power electronic equipment, the harmonics in the power grid are becoming more and more serious. There are many methods for harmonic mitigation and optimization such as Global network Optimization. When there are many nodes, the global network optimization method is more complicated. Considering the problem of large numbers of harmonic injection nodes in the power grid, this paper proposes a method of clustering the voltage distortion nodes according to correlation, and using the characteristic nodes to describe the harmonic voltage distortion in the region to mitigate harmonic voltage. This method is based on the observation data of the voltage distortion of the nodes for dynamic selection and grouping. The results show that this method meets the needs of Global network Optimization. The data processing methods used in this paper such as feature extraction methods and time series interpolation optimization can effectively reduce the data dimension, and get better optimization effect.