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Author: search.filters.author.Shih, Min-HsiungSubject: search.filters.subject.phosphor

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Now showing 1 - 7 of 7
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    Luminous efficiency enhancement of white light-emitting diodes by using a hybrid phosphor structure
    (2015-02-19)
    Lin, Bing-Cheng
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    Huang, Jhih-Kai
    ;
    Chen, Kuo-Ju
    ;
    Chiu, Sheng-Huan
    ;
    Tu, Zong-Yi
    This paper presents a "hybrid" structure for the coating of yellow YAG: Ce3(+) phosphor on blue GaN-based light-emitting diodes (LEDs). The luminous efficiency of the hybrid phosphor structure improved by 5.9% and 11.7%, compared with the conventional remote and conformal phosphor structures, respectively, because of the increased intensity of the yellow component. The hybrid structure also has an advantage in the phosphor usage reduction for the LEDs. Furthermore, the electric intensity of the hybrid phosphor structure was calculated for various thicknesses by conducting TFCalc32 simulation, and the enhanced utilization of blue rays was verified. Finally, the experimental results were consistent with the simulation results performed using the Monte-Carlo method. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
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    High-efficiency and low assembly-dependent chip-scale package for white light-emitting diodes
    (2015-04-21)
    Huang, Che-Hsuan
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    Chen, Kuo-Ju
    ;
    Tsai, Ming-Ta
    ;
    Shih, Min-Hsiung
    ;
    Sun, Chia-Wei
    This article presents a chip-scale package (CSP) with conformal and uniform structures for white light-emitting diodes used in lighting and backlight unit (BLU) applications. The CSP structures produce higher light extraction efficiency and lower assembly-dependent packaging compared with conventional surface-mounted devices (SMDs). Simulation results show that compared with SMDs, the luminous efficiency of CSP structures is 8.81% higher in lighting applications and 9.43% higher in BLU applications. This is likely due to light loss in the light bowl of the SMDs. Moreover, CSPs with a conformal phosphor structure exhibit low assembly dependence and redundancy, and rb-CSPs with a conformal structure are a more effective light source in both lighting and BLU applications. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
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    An Investigation of the Optical Analysis in White Light-Emitting Diodes With Conformal and Remote Phosphor Structure
    (2013-11-01)
    Chen, Kuo-Ju
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    Chen, Hsin-Chu
    ;
    Lin, Chien-Chung
    ;
    Wang, Chao-Hsun
    ;
    Yeh, Chia-Chi
    An effective emission model of phosphor film is proposed by using bidirectional scattering distribution function system (BSDF), and the model is verified by white light-emitting diodes (LEDs) with conformal and remote phosphor structure. The emission model is built to clarify the optical characteristics by analyzing the angular-dependent distribution of emission and excitation behaviors in phosphor film. The white LEDs with conformal and remote phosphor structure are also fabricated for experimental comparison. The uniformity of angular correlated color temperature (CCT) in white LEDs can be determined by the angular distribution of blue and yellow light, which is in turns decided by the refractive index variation between chip a (c) nd phosphor layers. Finally, the experimental results are found to have good agreement with the simulation results performing by the Monte Carlo method.
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    Improving the Angular Color Uniformity of Hybrid Phosphor Structures in White Light-Emitting Diodes
    (2013-10-01)
    Chen, Kuo-Ju
    ;
    Han, Hau-Vei
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    Lin, Bing-Cheng
    ;
    Chen, Hsin-Chu
    ;
    Shih, Min-Hsiung
    This letter examines a hybrid phosphor structure for white light-emitting diodes. The hybrid phosphor structure produces more efficient luminosity and more uniform angular correlated color temperature (CCT) than the conventional dispensing method. The experimental results show that the CCT deviation improved from 453 to 280 K between -70 degrees and 70 degrees. This was likely caused by the large blue light divergent angle. The lumen output produced was higher than that produced by dispense and conformal phosphor structures. Therefore, the results show that the hybrid phosphor structure can be used in solid-state lighting.
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    Enhanced Luminous Efficiency of WLEDs Using a Dual-Layer Structure of the Remote Phosphor Package
    (2013-06-15)
    Chen, Kuo-Ju
    ;
    Chen, Hsin-Chu
    ;
    Shih, Min-Hsiung
    ;
    Wang, Chao-Hsun
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    Tsai, Hsin-Han
    This study demonstrates how the insertion of a thin silicone layer into a dual-layer remote phosphor structure enhances light extraction in white light-emitting diodes (WLEDs). In the experiment, a dual-layer phosphor structure yielded a higher intensity of blue and yellow components than a conventional structure. Moreover, the lumen flux was 5% higher than a conventional remote phosphor package at the same correlated color temperature (CCT). Using a TFCalc32 simulation, the electric field intensity was calculated for different thicknesses of the dual-layer remote phosphor structures, and the enhanced use of blue rays was verified. Additionally, the dual-layer structure reduces chromaticity deviations as the driving current increases.
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    Efficiency and Droop Improvement in Hybrid Warm White LEDs Using InGaN and AlGaInP High-Voltage LEDs
    (2013-04-01)
    Chen, Kuo-Ju
    ;
    Kuo, Hsuan-Ting
    ;
    Chiang, Yen-Chih
    ;
    Chen, Hsin-Chu
    ;
    Wang, Chao-Hsun
    This study investigates the optical and electrical characteristics in hybrid warm white high-voltage light-emitting diodes (HV-LEDs). The luminous efficiency of the hybrid warm white LED in this study improved by 11% and 51%, compared to conventional cool and warm LEDs, respectively, solving the warm white gap in white LEDs. The efficiency droop of the hybrid warm white LED was reduced to 21.8% from 26.8% for the conventional cool white LED, and from 26.3% in the conventional warm white LED at 40 mA (35 A/cm(2)) the operated current. Furthermore, the color rendering index (CRI) and angular correlated color temperature (CCT) were analyzed, indicating a significant improvement in hybrid warm white HV-LEDs.
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    The Influence of the Thermal Effect on CdSe/ZnS Quantum Dots in Light-Emitting Diodes
    (2012-07-15)
    Chen, Kuo-Ju
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    Chen, Hsin-Chu
    ;
    Shih, Min-Hsiung
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    Wang, Chao-Hsun
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    Kuo, Ming-Yen
    This study investigates the effect of temperature on CdSe/ZnS quantum dots (QDs) in GaN-based light-emitting diodes (LEDs) using the phosphor conversion efficiency (PCE) and LED junction temperature. In our simulation, the blue chip and CdSe/ZnS QDs temperature are similar because of their minimal thickness. Furthermore, to verify the effect of temperature on CdSe/ZnS QDs, we use continuous wave and pulsed current sources to measure the relationship between the temperature and relative PCE. Higher junction temperatures are observed with greater CdSe/ZnS QD volume in LEDs. This is attributed to the thermal conduction and nonradiative energy between CdSe/ZnS QDs and blue chip. Therefore, if thermal management is improved, CdSe/ZnS QDs are expected to be used as color converting material in LEDs.