Eu²⁺-doped Ba₂GaB₄O₉Cl blue-emitting phosphor with high color purity for near-UV-pumped white light-emitting diodes

Gao, Z.,Deng, H.,Xue, N.,Jeong, J.H.,Yu, R. Elsevier Advanced Technology 2018 OPTICS AND LASER TECHNOLOGY Vol.98 No.-

<P>Eu2+-doped borate fluoride Ba(2)GaB(4)O(9)C1 was synthesized by the conventional high-temperature solidstate reaction. The crystal structure and luminescence properties of the phosphors, as well as their thermal luminescence quenching capabilities and CIE chromaticity coordinates were systematically investigated. Under the excitation at 340 nm, the phosphor exhibited an asymmetric broad-band blue emission with a peak at 445 nm, which is ascribed to the 4f-5d transition of Eu2+. It was further proved that energy transfer among the nearest neighbor ions is the major mechanism for concentration quenching of Eu2+ in Ba-2,GaB(4)O(9)C1:xEu(2+) phosphors. The luminescence quenching temperature is 432 K. The CIE color coordinates are very close to those of BaMgA110017:Eu2+ (BAM). All the properties indicated that the blue emitting Ba(2)GaB(4)O(9)C1:Eu2+ phosphor has potential application in white LEDs. (C) 2017 Elsevier Ltd. All rights reserved.</P>

Effects of momentum transfer on sizing of current collectors for lithium-ion batteries during laser cutting

Lee, D.,Mazumder, J. Elsevier Advanced Technology 2018 OPTICS AND LASER TECHNOLOGY Vol.99 No.-

<P>One of the challenges of the lithium-ion battery manufacturing process is the sizing of electrodes with good cut surface quality. Poor cut surface quality results in internal short circuits in the cells and significant heat generation. One of the solutions that may improve the cut quality with a high cutting speed is laser cutting due to its high energy concentration, fast processing time, high precision, small heat affected zone, flexible range of laser power and contact free process. In order to utilize the advantages of laser electrode cutting, understanding the physical phenomena for each material is crucial. Thus, this study focuses on the laser cutting of current collectors, such as pure copper and aluminum. A 3D self consistent mathematical model for the laser cutting, including fluid flow, heat transfer, recoil pressure, multiple reflections, capillary and thermo-capillary forces, and phase changes, is presented and solved numerically. Simulation results for the laser cutting are analyzed in terms of penetration time, depth, width, and absorptivity, based on these selected laser parameters. In addition, melt pool flow, melt pool geometry and temperature distribution are investigated. (C) 2017 Elsevier Ltd. All rights reserved.</P>

Effects of process parameters on properties of porous foams formed by laser-assisted melting of steel powder (AISI P21)/foaming agent (ZrH₂) mixture

Seo, J.Y.,Lee, K.Y.,Shim, D.S. Elsevier Advanced Technology 2018 Optics and laser technology Vol.98 No.-

<P>This paper describes the fabrication of lightweight metal foams using the directed energy deposition (DED) method. DED is a highly flexible additive manufacturing process wherein a metal powder mixed with a foaming agent is sprayed while a high-power laser is used to simultaneously melt the powder mixture into layered metal foams. In this study, a mixture of a carbon steel material (P21 powder) and a widely used foaming agent, ZrH2, is used to fabricate metal foams. The effects of various process parameters, such as the laser power, powder feed rate, powder gas flow rate, and scanning speed, on the deposition characteristics (porosity, pore size, and pore distribution) are investigated. The synthesized metal foams exhibit porosities of 10% or lower, and a mean pore area of 7 x 10(5) mu m(2). It is observed that the degree of foaming increases in proportion to the laser power to a certain extent. The results also show that the powder feed rate has the most pronounced effect on the porosity of the metal foams, while the powder gas flow rate is the most suitable parameter for adjusting the size of the pores formed within the foams. Further, the scanning speed, which determines the amounts of energy and powder delivered, has a significant effect on the height of the deposits as well as on the properties of the foams. Thus, during the DED process for fabricating metal foams, the pore size and distribution and hence the foam porosity can be tailored by varying the individual process parameters. These findings should be useful as reference data for the design of processes for fabricating porous metallic materials that meet the specific requirements for specialized parts. (C) 2017 Elsevier Ltd. All rights reserved.</P>

A study on the edge chipping according to spindle speed and inclination angle of workpiece in laser-assisted milling of silicon nitride

Woo, W.S.,Lee, C.M. Elsevier Advanced Technology 2018 Optics and laser technology Vol.99 No.-

<P>Ceramics are difficult to machine due to their high hardness and brittleness. As an effective method for machining ceramics, laser-assisted machining (LAM) has been studied by many researchers. In particular, many studies of methods to improve the machinability of silicon nitride using LAM have been performed. However, there is little research on the effect of the inclination angle of the workpiece, because varying the angle increases the difficulty of controlling the laser preheating and tool path. This paper investigates the effect of preheating temperature, spindle speed and inclination angle of the workpiece on edge chipping of silicon nitride in an effort to obtain an enhanced surface finish using laser-assisted milling (LAMill). The machining conditions were determined by considering the parameters that can reduce edge chipping using related theory. Experimental results showed a reduction in edge chipping based on increases in preheating temperature, spindle speed and inclination angle of the workpiece. Also, by increasing the spindle speed and the inclination angle of the workpiece, surface roughness was decreased due to reduction in the cutting force. The energy efficiency of LAMill by comparing the specific cutting energy according to the machining conditions is analyzed. (C) 2017 Elsevier Ltd. All rights reserved.</P>

Analysis of roll-stamped light guide plate fabricated with laser-ablated stamper

Na, H.,Hong, S.,Kim, J.,Hwang, J.,Joo, B.,Yoon, K.,Kang, J. Elsevier Advanced Technology 2017 Optics and laser technology Vol.97 No.-

LGP (light guide plate) is one of the major components of LCD (liquid crystal display), and it makes surface illumination for LCD backlit. LGP is a transparent plastic plate usually produced by injection molding process. On the back of LGP there are micron size patterns for extraction of light. Recently a roll-stamping process has achieved the high mass productivity of thinner LGPs. In order to fabricate optical patterns on LGPs, a fabricating tool called as a stamper is used. Micro patterns on metallic stampers are made by several micro machining processes such as chemical etching, LIGA-reflow, and laser ablation. In this study, a roll-stamping process by using a laser ablated metallic stamper was dealt with in consideration of the compatibility with the roll-stamping process. LGP fabricating tests were performed using a roll-stamping process with four different roll pressures. Pattern shapes on the stamper fabricated by laser ablation and transcription ratios of the roll-stamping process were analyzed, and LGP luminance was evaluated. Based on the evaluation, optical simulation model for LGP was made and simulation accuracy was evaluated. Simulation results showed good agreements with optical performance of LGPs in the brightness and uniformity. It was also shown that the roll-stamped LGP has the possibility of better optical performance than the conventional injection molded LGP. It was also shown that the roll-stamped LGP with the laser ablated stamper is potential to have better optical performance than the conventional injection molded LGP.