Browsing by Author "Chen, T. M."

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Effect of Mn substitution on electronic structure of Ca(9)Y(PO(4))(7):Eu(2+), Mn(2+) phosphor determined by X-ray absorption spectroscopy
(2011-10-27)
Lu, Y. R.
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Huang, C. H.
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Chen, T. M.
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Lin, J. H.
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Ma, Y. R.
The single-composition Ca(9)Y(PO(4))(7):Eu(2+), Mn(2+) phosphors were synthesized by a solid-state reaction. The luminescent properties and electronic structures were investigated by photoluminescence (PL) and X-ray absorption near-edge structure (XANES). The PL demonstrated energy transfer and a red-shift as the Mn doping level was increased. The energy transfer is ascribed to charge transfer between Eu and Mn. The change of the PL intensity is caused by the increased O 2p-Mn 3d hybridization. The narrowing of the band gap, which finding is supported by the red-shift, is responsible for the formation of the Mn-related states close to the conduction band minimum. (C) 2011 Elsevier B.V. All rights reserved.
Effect of Mn substitution on electronic structure of Ca9Y(PO4)(7):Eu2+, Mn2+ phosphor determined by X-ray absorption spectroscopy
(2011-10-27)
Lu, Y. R.
;
Huang, C. H.
;
Chen, T. M.
;
Lin, J. H.
;
Ma, Y. R.
The single-composition Ca9Y(PO4)(7):Eu2+, Mn2+ phosphors were synthesized by a solid-state reaction. The luminescent properties and electronic structures were investigated by photoluminescence (PL) and X-ray absorption near-edge structure (XANES). The PL demonstrated energy transfer and a red-shift as the Mn doping level was increased. The energy transfer is ascribed to charge transfer between Eu and Mn. The change of the PL intensity is caused by the increased O 2p-Mn 3d hybridization. The narrowing of the band gap, which finding is supported by the red-shift, is responsible for the formation of the Mn-related states close to the conduction band minimum. (C) 2011 Elsevier B.V. All rights reserved.
Efficiency improvement of Si solar cells using metal-enhanced nanophosphor fluorescence
(2014-01-01)
Chen, J. -Y.
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Huang, C. K.
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Hung, W. B.
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Sun, K. W.
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Chen, T. M.
In this study, Eu2+-doped barium silicate (Ba2SiO4:Eu2+) nanophosphors dispersed in a surfactant solution were spin-coated on commercially available silicon solar cells to form colloidal crystals on the surface. The crystals then act as luminescence down-shifting centers to generate low-energy photons for incident ultraviolet light. The fluorescence from the Ba2SiO4:Eu2+ nanophosphors was further enhanced by coating a metal-enhanced layer composed of Ag nanoparticles and a SiO2 spacer. The solar cells showed an enhancement of 0.86 mA/cm(2) in short-circuit current density and approximately 0.64% increase in power conversion efficiency when coated with nanophosphors, SiO2 spacers, and Ag nanoparticles. The properties of cells integrated with the metal-enhanced layer were characterized to identify the roles of nanophosphors and Ag nanoparticles in improved light harvesting. These experiments demonstrated that the colloids of Ba2SiO4:Eu2+ acted as luminescence down-shifting centers in the ultraviolet region and the metallic nanoparticles also helped to enhance fluorescence in the visible region to increase light absorption within the measured spectral regime. (C) 2013 Elsevier B.V. All rights reserved.
Enhanced light harvesting of Si solar cells via luminescent down-shifting using YVO4:Bi3+, Eu3+ nanophosphors
(2013-11-01)
Huang, C. K.
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Chen, Y. C.
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Hung, W. B.
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Chen, T. M.
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Sun, K. W.
The colloids of YVO4 nanoparticles on microtextured Si surface are demonstrated to have promising potential for efficient solar spectrum utilization in crystalline Si solar cells. The solar cells showed an enhancement of 4% in short-circuit current density and approximately 0.7% in power conversion efficiency when coated with YVO4 nanoparticles. The properties of cells integrated with YVO4 nanoparticles were characterized to identify the role of YVO4 in improved light harvesting. The current experiments conclude that the colloids of YVO4 nanoparticles not only act as luminescent down-shifting centers in the ultraviolet region but also serve as an antireflection coating for enhancing the light absorption in the measured spectral regime. Copyright (c) 2012 John Wiley & Sons, Ltd.
Excellent Color Rendering Index Quantum Dots White Light-Emitting Diode with Distributed Bragg Reflector Structure
(2014)
Chen, K. J.
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Lin, B. C.
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Han, H. V.
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Lin, C. C.
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Lee, C. Y.
This study demonstrated the high CRI and excellent uniformity colloidal quantum dot white-light-emitting diodes with the DBR structure at different correlated color temperature from 2500 K to 4500K.
Hybrid White Light-emitting Diodes by Organic-Inorganic materials
(2015)
Chen, K. J.
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Lai, Y. C.
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Lin, B. C.
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Lin, C. C.
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Chiu, S. H.
This study demonstrated the high uniformity hybrid white light-emitting didoes with polyfluoren (PFO) polymer and quantum dot (QD) with different CCT range from 3000K to 9000K.
Study of a Nanoparticle Charger Containing Multiple Discharging Wires in a Tube
(2008)
Tsai, C. J.
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Chen, S. C.
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Chen, H. L.
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Chein, H. M.
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Wu, C. H.
A unipolar charger containing multiple discharging wires in a tube (inner diameter: 50mm) was developed and tested in order to increase the aerosol flow rate and the charging efficiency of nanoparticles. Four gold wires of 25 mm in diameter and 15 mm in length were used as the discharging electrodes to generate positive ions (Ni) from 2.72 x 10(8) ions/cc to 3.87 x 10(9) ions/cc in concentration at the discharging voltage of + 4.0 similar to + 10 KV. Monodisperse NaCl particles of 10 similar to 50nm in diameter were used to test the charging efficiency and the particle loss of charged particles with different aerosol flow rates, corona voltages and sheath flow rates. The sheath air near the tube wall was found to increase the extrinsic charging efficiency, and the highest efficiency was obtained at + 6.0KV discharging voltage, 10 L/min aerosol flow rate and 9 L/min sheath flow rate. The extrinsic charging efficiency increased from 10.6% to 74.2% when the particle diameter was increased from 10 to 50 nm. The TDMA (tandem differential mobility analyzer) method was used to determine the charge distribution and the mean charge per particle and it was found that the Fuchs charging theory corrected for the extrinsic charging efficiency matched with the experimental data very well.
Synthesis, luminescence and application of BaKYSi2O7:Eu2+ : A new blue-emitting phosphor for near-UV white-light LED
(2018-05-01)
Ray, Sudeshna
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Tadge, Prachi
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Dutta, Somrita
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Chen, T. M.
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Nair, Govind B.
A series of new silicate phosphors, Ba1-xEuxKYSi2O7 (BKY: Eu2+) (x = 0.005, 0.01, 0.02, 0.05, 0.07) have been synthesized from a water-soluble propylene glycol modified silane (PGMS) based silicon precursor by a solution approach. This phosphor can be efficiently excited by near-UV light and generates a broadband bright blue emission with internal Quantum Efficiency 34%. The detailed crystal structure of monoclinic BKY:Eu2+ was determined from the XRD profile using Rietveld refinement. Band gap was determined from Diffuse Reflectance Spectra using Kubelka Munk function. Steady state and time resolved Photoluminescence measurement as well as the thermal quenching properties of the phosphor have been investigated in detail. A highly efficient broadband blue emission centered lambda(max) similar to 460 nm with a full-width at half-maximum of 72 nm shows very low thermal quenching; 83.2% at 150 degrees C with respect to that measured at room temperature. Moreover, a white LED device has been fabricated by coating the as-synthesized phosphor with a standard red emitting CaAlSiN3:Eu2+ phosphor and a standard green emitting Ba2SiO4:Eu2+ phosphor. The LED device exhibited an excellent color-rendering index CRI of 84.0564 at a correlated color temperature of 3752.4 K with CIE color coordinates of (0.363, 0.293) under a 350 mA forward-bias current. The interesting excitation profile and robust thermal performance reflect the potential application of this phosphor for near UV- LED driven solid state lighting.