Browsing by Author "Wu, Yun-Chen"

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A Novel Tunable Green- to Yellow-Emitting beta-YFS:Ce(3+) Phosphor for Solid-State Lighting
(2011-08-01)
Wu, Yun-Chen
;
Wang, De-Yin
;
Chen, Teng-Ming
;
Lee, Chi-Shen
;
Chen, Kuo-Ju
A Ce(3+)-activated fluorosulfide phosphor (beta-YFS: Ce(3+)) was synthesized by solid-state reaction in a sealed tube. The crystal structure has been refined from the XRD profiles and there are two different crystallographic rare earth sites, namely, Y(1) and Y(2), where the Ce(3+) ions occupied. The emission band with a maximum at 495 nm of beta-Y(0.99)Ce(0.01) FS phosphor was characterized by the 4f-5d transitions of Ce(3+) ion. With increasing Ce(3+) concentration, the emission variations were observed from 495 to 547 nm. When beta-YFS:Ce(3+) phosphors were utilized to incorporate with n-UV/blue chip, greenish-white light with color rendering index of 65-77 were obtained. The results indicate that the tunable green- to yellow-emitting beta-YFS:Ce(3+) can serve as a potential phosphor for incorporation in fabrication for solid-state lighting. The preparation, spectroscopic characterization, quantum efficiency, thermal-quenching behavior, and related LED device data are also presented.
A Novel Tunable Green- to Yellow-Emitting beta-YFS:Ce3+ Phosphor for Solid-State Lighting
(2011-08-01)
Wu, Yun-Chen
;
Wang, De-Yin
;
Chen, Teng-Ming
;
Lee, Chi-Shen
;
Chen, Kuo-Ju
A Ce3+-activated fluorosulfide phosphor (beta-YFS: Ce3+) was synthesized by solid-state reaction in a sealed tube. The crystal structure has been refined from the XRD profiles and there are two different crystallographic rare earth sites, namely, Y(1) and Y(2), where the Ce3+ ions occupied. The emission band with a maximum at 495 nm of beta-Y0.99Ce0.01 FS phosphor was characterized by the 4f-5d transitions of Ce3+ ion. With increasing Ce3+ concentration, the emission variations were observed from 495 to 547 nm. When beta-YFS:Ce3+ phosphors were utilized to incorporate with n-UV/blue chip, greenish-white light with color rendering index of 65-77 were obtained. The results indicate that the tunable green- to yellow-emitting beta-YFS:Ce3+ can serve as a potential phosphor for incorporation in fabrication for solid-state lighting. The preparation, spectroscopic characterization, quantum efficiency, thermal-quenching behavior, and related LED device data are also presented.
alpha-(Y,Gd)FS:Ce(3+): a novel red-emitting fluorosulfide phosphor for solid-state lighting
(2011-01-01)
Wu, Yun-Chen
;
Chen, Yi-Chin
;
Wang, De-Yin
;
Lee, Chi-Shen
;
Sun, Ching-Cherng
A novel Ce(3+)-doped fluorosulfide phosphor, alpha-(Y,Gd)FS:Ce(3+), was first investigated as a new candidate for application in phosphor-converted light emitting diodes (LEDs) and thin-film electroluminescence (TFEL) devices. The detailed crystal structure was investigated based on X-ray diffraction profiles using Rietveld refinement methods. This phosphor shows good absorption ranging from ultraviolet to visible region and broad saturated red emission, which can be tuned from 660 to 672 nm, and the photoluminescence (PL) intensity was demonstrated to be effectively enhanced by Gd(3+) substitution.
alpha-(Y,Gd)FS:Ce3+: a novel red-emitting fluorosulfide phosphor for solid-state lighting
(2011-01-01)
Wu, Yun-Chen
;
Chen, Yi-Chin
;
Wang, De-Yin
;
Lee, Chi-Shen
;
Sun, Ching-Cherng
A novel Ce3+-doped fluorosulfide phosphor, alpha-(Y,Gd)FS:Ce3+, was first investigated as a new candidate for application in phosphor-converted light emitting diodes (LEDs) and thin-film electroluminescence (TFEL) devices. The detailed crystal structure was investigated based on X-ray diffraction profiles using Rietveld refinement methods. This phosphor shows good absorption ranging from ultraviolet to visible region and broad saturated red emission, which can be tuned from 660 to 672 nm, and the photoluminescence (PL) intensity was demonstrated to be effectively enhanced by Gd3+ substitution.
Anomalous luminescence from Yb2+-doped Ca2PO4Cl
(2014-04-01)
Wang, De-Yin
;
Chiu, Yi-Chen
;
Huang, Chien-Hao
;
Wu, Yun-Chen
;
Chen, Teng-Ming
The photoluminescence of Ca2PO4Cl:Yb2+ has been investigated and compared with that of Ca2PO4Cl: Eu2+, and the application of Ca2PO4Cl:Yb2+ for white LED has been evaluated. The excitation spectra of Ca2PO4Cl:Yb2+ are dominated by an intense excitation band at 395 nm. Under near DV excitation at 395 nm, Ca2PO4Cl:Yb2+ shows a broad asymmetric emission with maximum at 490 nm. This emissions result from two different Yb2+ centers is evidenced by the low temperature (T=100 K) emission spectrum. Yb2+ luminescence differs significantly from that of Eu2+, most notably in the structure of emission spectra, and is characterized by a much broader emission band and lower quenching temperature. Such anomalous luminescence from Yb2+ is ascribed to the de-excitation process of the Yb2+-trapped exciton state. Ca2PO4Cl:Yb2+ has external quantum efficiency of 24% and exhibits 40% of luminescence quenching at 100 degrees C in the air and, therefore, these results reveal its limited potential in the fabrication of white-light LEDs. (C) 2013 Elsevier B.V. All rights reserved.
BaZrSi(3)O(9):Eu(2+): a cyan-emitting phosphor with high quantum efficiency for white light-emitting diodes
(2011-01-01)
Wang, De-Yin
;
Huang, Chien-Hao
;
Wu, Yun-Chen
;
Chen, Teng-Ming
;
應用化學系
In this paper, a cyan-emitting phosphor BaZrSi(3)O(9):Eu(2+) was synthesized and evaluated as a candidate for white light emitting diodes (WLEDs). This phosphor shows strong and broad absorption in 380-420 nm region, and the emission intensity of the optimized BaZrSi(3)O(9):Eu(2+) was found to be 90% and 198% of that of the commercial BaMgAl(10)O(17):Eu(2+) (BAM:Eu(2+)) under excitation at 405 nm and 420 nm, respectively. Upon excitation at 405 nm, the quantum efficiency of the optimized BaZrSi(3)O(9):Eu(2+) is 83% of that of BAM:Eu(2+). The performance of this phosphor was further tested to fabricate white LED lamps. By coating BaZrSi(3)O(9):Eu(2+) with a green-emitting (Ba,Sr)(2)SiO(4):Eu(2+) and a red-emitting CaAlSiN(3):Eu(2+) on a near-ultraviolet (405 nm) LED chip, driven by a 350 mA forward bias current, intense warm white light with a color rendering index of 90 has been produced.
BaZrSi3O9:Eu2+: a cyan-emitting phosphor with high quantum efficiency for white light-emitting diodes
(2011-01-01)
Wang, De-Yin
;
Huang, Chien-Hao
;
Wu, Yun-Chen
;
Chen, Teng-Ming
;
應用化學系
In this paper, a cyan-emitting phosphor BaZrSi3O9:Eu2+ was synthesized and evaluated as a candidate for white light emitting diodes (WLEDs). This phosphor shows strong and broad absorption in 380-420 nm region, and the emission intensity of the optimized BaZrSi3O9:Eu2+ was found to be 90% and 198% of that of the commercial BaMgAl10O17:Eu2+ (BAM:Eu2+) under excitation at 405 nm and 420 nm, respectively. Upon excitation at 405 nm, the quantum efficiency of the optimized BaZrSi3O9:Eu2+ is 83% of that of BAM:Eu2+. The performance of this phosphor was further tested to fabricate white LED lamps. By coating BaZrSi3O9:Eu2+ with a green-emitting (Ba,Sr)(2)SiO4:Eu2+ and a red-emitting CaAlSiN3:Eu2+ on a near-ultraviolet (405 nm) LED chip, driven by a 350 mA forward bias current, intense warm white light with a color rendering index of 90 has been produced.
Color-Tunable Fluorosulfide Phosphors for Solid-State Lighting: Structure and Luminescence Investigations
(2011)
Wu, Yun-Chen
;
Chen, Yi-Chin
;
Lee, Chi-Shen
;
Chen, Teng-Ming
;
應用化學系
A novel Y-2(Ca,Sr)F4S2:Ce3+ fluorosuffide phosphor, was synthesized and its crystal structure was refined with Rietveld method. Y-2(Ca,Sr)F4S2:Ce3+ can be efficiently excited by blue light and shows yellow-to-orange broadband emission at 553-590 nm. Possible mechanism of the tunable luminescence properties was explained on the basis of the band structure calculations.
Controlled synthesis and luminescent properties of monodispersed PEI-modified YVO4:Bi3+,Eu3+ nanocrystals by a facile hydrothermal process
(2012)
Chen, Yi-Chin
;
Wu, Yun-Chen
;
Wang, De-Yin
;
Chen, Teng-Ming
;
應用化學系
A series of water-soluble YVO4:Bi3+, Eu3+ nanocrystals, with surfaces functionalized by a branch polyethylenimine (BPEI) polymer, have been synthesized via a one-pot hydrothermal method. It was found that the particle size and crystal morphology could be efficiently controlled by different reaction temperatures, pH values and molecular weights of the BPEI polymer. The surface modification of the nanocrystals was characterized using Fourier transform infrared spectroscopy (FT-IR). The highly crystalline YVO4:Bi3+, Eu3+ nanoparticles, with an average diameter of 20 nm, can be dispersed in water due to the presence of amino ligands. When conjugated with biomolecules, the YVO4:Bi3+, Eu3+ nanocrystals retain their strong red emission, peaking at 619 nm under near-ultraviolet (n-UV) excitation. The results indicate that YVO4:Bi3+, Eu3+ nanocrystals can serve as a promising candidate for biological imaging, and immunoassay applications.
Crystal structure characterization, optical and photoluminescent properties of tunable yellow- to orange-emitting Y-2(Ca,Sr)F4S2:Ce3+ phosphors for solid-state lighting
(2012)
Wu, Yun-Chen
;
Chen, Yi-Chin
;
Chen, Teng-Ming
;
Lee, Chi-Shen
;
Chen, Kuo-Ju
In this study, a new efficient Ce3+-doped fluorosulfide phosphor, Y-2(Ca,Sr)F4S2:Ce3+, was obtained by using solid-state methods in a sealed silica ampoule. The synthesized Y-2(Ca,Sr)F4S2:Ce3+ was characterized by powder X-ray diffraction and refined with Rietveld methods. Y-2(Ca,Sr)F4S2:Ce3+ can be excited by blue light (440-470 nm) and shows yellow-to-orange broadband emission peaking at 553-590 nm with a quantum efficiency of 16-31%. Non-radiative transitions between Ce3+ ions in Y2CaF4S2:Ce3+ and Y2SrF4S2:Ce3+ hosts have also been demonstrated to be attributable to dipole-dipole interactions, and the critical distances were calculated to be 18.9 and 19.3 angstrom. The possible mechanism of the tunable luminescence properties was described on the basis of band structure calculations. In addition, a white LED device was fabricated by using Y-2(Ca,Sr)F4S2:Ce3+ phosphor pumped with a 460 nm blue chip. The CRI value and CCT were measured to be 74-85 and 3500-8700 K, respectively, showing promising potential for solid-state lighting.
High-Temperature Insensitivity of 50-Gb/s 16-QAM-DMT Transmission by Using the Temperature-Compensated Vertical-Cavity Surface-Emitting Lasers
(2018-08-15)
Peng, Chun-Yen
;
Tsai, Cheng-Ting
;
Wang, Huai-Yung
;
Wu, Yun-Chen
;
Shih, Tien-Tsorng
In this study, a 50-Gb/s 16-quadrature amplitude modulation discrete multitone (16-QAM-DMT) was applied to an 850-nm oxide-confined vertical-cavity surface-emitting laser (VCSEL) at various temperature ranging from 25 degrees C to 85 degrees C. This study reports the highest bit rate for directly modulated VCSELs operating at 85 degrees C, in addition to demonstrating, for the first time, 16-QAM-DMT with less dependence on slope efficiency (SE) reduction. By using a temperature-compensated VCSEL, this study determined the degradation of the bit error rate (BER) in terms of the signal-to-noise ratio. The analysis results demonstrate that the transmission quality is dominated by optical bandwidth rather than the SE. Therefore, the preleveling technique was applied for error rate recovery to reduce the BER from 6.3 x 10(-3) to 3.8 X 10(-3) with a 0.2-dB/GHz preleveling slope. Thus, a low-bandwidth system (nearly 10 GHz) was realized for high data-rate transmissions (50 Gb/s) at 85 degrees C. The 16-QAM-DMT transmission provides an effective approach to alleviating thermal problems that occur in high-speed optical communication without the requirement of any external amplification circuits.
Luminescence and Spectroscopic Properties of Yellow-Emitting Carbonitride Phosphors and Their Application in White LEDs
(2010)
Wu, Yun-Chen
;
Chen, Teng-Ming
;
Chiu, Chuang-Hung
;
Mo, Chi-Neng
;
應用化學系
A series of yellow-emitting carbonitride phosphors with compositions of (Y(1-x)Ce(x))(2)(CN(2))(3) (x = 0-0.1) was synthesized by using exothermic solid-state metathesis reactions. The wavelength of the broad band yellow emission was tunable, varying from 570 to 577 nm. The photoluminescence (PL) intensity enhanced with increasing Ce(3+) dopant content and was optimized at 3 mol % under excitation at 415 nm. We analyzed the 5d energy levels of Ce(3+) in a capped trigonal prismatic complex and estimated the vibronic coupling parameters and Stokes shifts. To understand the thermal quenching behavior, the temperature-dependent PL for (Y(1.97)Ce(0.03))(2)(CN(2))(3) was investigated. To demonstrate its potential application, we fabricated a warm white light-emitting diode (LED) using (Y(1.97)Ce(0.03))(2)(CN(2))(3), pumped with a 420 nm GaInN LED chip, and the electroluminescence data were also presented. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3476307] All rights reserved.
Modal Linewidth Dependent Transmission Performance of 850-nm VCSELs With Encoding PAM-4 Over 100-m MMF
(2017-10-01)
Kao, Hsuan-Yun
;
Chi, Yu-Chieh
;
Peng, Chun-Yen
;
Leong, Shan-Fong
;
Chang, Chun-Kai
By changing the transverse-mode spectral linewidth of vertical cavity surface emitting lasers (VCSELs) at 850 nm, the directly encoded four-level pulse amplitude modulation data transmission performance over 100-m-long OM4 multimode fiber (MMF) are demonstrated and compared. The multi-mode VCSEL chip with the largest aperture of 11 mu m reveals the widest spectral linewidth and the highest optical power, but provides the smallest modulation bandwidth to support only 44-and 28-Gb/s data rates for back-to-back (BtB) and 100-m OM4 MMF transmission cases, respectively. By shrinking the aperture size to reduce transverse-mode number, the few-mode VCSEL with the strongest throughput power enables a BtB transmission capacity as high as 52 Gb/s. However, its modal dispersion induced after OM4 MMF transmission inevitably degrade the data rate to 32 Gb/s. In contrast, the single-mode VCSEL with the smallest aperture of 3 mu m reveals the highest modulation bandwidth and negligible modal dispersion to show competitive BtB transmission capacity with that of the few-mode VCSEL. In particular, the single-mode VCSEL successfully achieves a data rate of 34 Gb/s with a power penalty as low as 1.4 dB, after 100-m OM4 MMF transmission.
Pre-leveled 16-QAM OFDM Modulation of an 850-nm VCSEL for 56-Gbit/s Transmission
(2016)
Tsai, Cheng-Ting
;
Pong, Chun-Yen
;
Wu, Yun-Chen
;
Leong, Shan-Fong
;
Chi, Yu-Chieh
An 850-nm VCSEL carried 16-QAM OFDM transmission at 56 Gbit/s is demonstrated by using the pre-leveling technology, which reveals an optimized signal-to-noise ratio, error vector magnitude and bit-error-rate of 16. 4 dB, 15.1 % and 1.2 x10(-3), respectively.
Synthesis, crystal structure, and photoluminescence of a novel blue-green emitting phosphor: BaHfSi(3)O(9):Eu(2+)
(2011-01-01)
Wang, De-Yin
;
Wu, Yun-Chen
;
Chen, Teng-Ming
;
應用化學系
;
Department of Applied Chemistry
BaHfSi(3)O(9) with barizite structure was synthesized and its detailed crystal structure was determined from the XRD profiles using Rietveld refinement. Pristine BaHfSi(3)O(9) shows bright blue emission under UV excitation. The blue emission was proved to be related to the charge transfer luminescence from Ti(4+), which presented as an impurity in the starting material HfO(2). The BaHfSi(3)O(9):Eu(2+) phosphor has been evaluated as a color converter for white LEDs. The results show that BaHfSi(3)O(9):Eu(2+) can be efficiently excited by near-ultraviolet (n-UV) of 380-420 nm and yield an intense blue-green emission. Upon excitation at 405 nm, the absorption and quantum efficiency for BaHfSi(3)O(9):Eu(2+) with optimal composition is about 78% and 50%, respectively. In addition, BaHfSi(3)O(9):Eu(2+) demonstrates high thermal stability, as shown by its luminescence intensity at 150 degrees C maintains about similar to 86% of that at room temperature. The performance of this phosphor was further tested to fabricate white LED lamps. By coating BaHfSi(3)O(9):Eu(2+) with a green-emitting (Ba,Sr)(2)SiO(4):Eu(2+) and a red-emitting CaAlSiN(3):Eu(2+) on an n-UV (405 nm) LED chip, driven by a 150 mA forward bias current, intense warm white light with a color rendering index of 91 was produced.
Synthesis, crystal structure, and photoluminescence of a novel blue-green emitting phosphor: BaHfSi3O9:Eu2+
(2011-01-01)
Wang, De-Yin
;
Wu, Yun-Chen
;
Chen, Teng-Ming
;
應用化學系
;
Department of Applied Chemistry
BaHfSi3O9 with barizite structure was synthesized and its detailed crystal structure was determined from the XRD profiles using Rietveld refinement. Pristine BaHfSi3O9 shows bright blue emission under UV excitation. The blue emission was proved to be related to the charge transfer luminescence from Ti4+, which presented as an impurity in the starting material HfO2. The BaHfSi3O9:Eu2+ phosphor has been evaluated as a color converter for white LEDs. The results show that BaHfSi3O9:Eu2+ can be efficiently excited by near-ultraviolet (n-UV) of 380-420 nm and yield an intense blue-green emission. Upon excitation at 405 nm, the absorption and quantum efficiency for BaHfSi3O9:Eu2+ with optimal composition is about 78% and 50%, respectively. In addition, BaHfSi3O9:Eu2+ demonstrates high thermal stability, as shown by its luminescence intensity at 150 degrees C maintains about similar to 86% of that at room temperature. The performance of this phosphor was further tested to fabricate white LED lamps. By coating BaHfSi3O9:Eu2+ with a green-emitting (Ba,Sr)(2)SiO4:Eu2+ and a red-emitting CaAlSiN3:Eu2+ on an n-UV (405 nm) LED chip, driven by a 150 mA forward bias current, intense warm white light with a color rendering index of 91 was produced.