Measurement and numerical studies of optical properties of YAG:Ce phosphor for white light-emitting diode packaging
TL;DR: Comparisons revealed that Mie theory can predict the variation of the optical constants of phosphor, but the absorption and scattering cross sections should be multiplied with two fitting parameters.
Abstract: The optical properties of YAG:Ce phosphor were measured by a double-integrating-sphere system and calculated by Mie theory and Monte Carlo ray tracing to provide precise optical characterizations of YAG:Ce phosphor for white light-emitting diode (LED) packaging design. Measurement results showed that the phosphor presents strong absorption for blue light, high reflection for yellow light, and an isotropic emission pattern of converted light. The conversion efficiency and quantum efficiency for the saturated phosphor are around 70% and 87%, respectively. Based on the measurement results, the absorption coefficient, scattering coefficient, and anisotropy factor of the phosphor calculated by Mie theory were compared with those calculated by ray-tracing simulation to modify Mie theory to find a reasonable method that can easily obtain the optical constants of YAG:Ce phosphor. Comparisons revealed that Mie theory can predict the variation of the optical constants of phosphor, but the absorption and scattering cross sections should be multiplied with two fitting parameters. The fitting parameters have been given in this study and can be obtained by testing packaged LEDs with different phosphor concentrations.
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TL;DR: A general overview of state-of-the-art LED lighting, discussing the main characteristics required of both quantum wells and color converters to efficiently generate white light and the main challenges in this field as well as the potential of metallic nanostructures to circumvent them.
Abstract: Light-emitting diodes (LEDs) are driving a shift toward energy-efficient illumination. Nonetheless, modifying the emission intensities, colors and directionalities of LEDs in specific ways remains a challenge often tackled by incorporating secondary optical components. Metallic nanostructures supporting plasmonic resonances are an interesting alternative to this approach due to their strong light-matter interaction, which facilitates control over light emission without requiring external secondary optical components. This review discusses new methods that enhance the efficiencies of LEDs using nanostructured metals. This is an emerging field that incorporates physics, materials science, device technology and industry. First, we provide a general overview of state-of-the-art LED lighting, discussing the main characteristics required of both quantum wells and color converters to efficiently generate white light. Then, we discuss the main challenges in this field as well as the potential of metallic nanostructures to circumvent them. We review several of the most relevant demonstrations of LEDs in combination with metallic nanostructures, which have resulted in light-emitting devices with improved performance. We also highlight a few recent studies in applied plasmonics that, although exploratory and eminently fundamental, may lead to new solutions in illumination.
156 citations
TL;DR: In this article, the authors summarized the recent progress in the packaging of QD-LEDs and discussed the wide applications of QDs in lighting and display, followed by the challenges and corresponding progresses for the QDLEDs' packaging.
Abstract: Recent years, semiconductor quantum dots (QDs) have attracted tremendous attentions for their unique characteristics for solid-state lighting (SSL) and thin-film display applications. The pure and tunable spectra of QDs make it possible to simultaneously achieve excellent color-rendering properties and high luminous efficiency (LE) when combining colloidal QDs with light-emitting diodes (LEDs). Due to its solution-based synthetic route, QDs are impractical for fabrication of LED. QDs have to be incorporated into polymer matrix, and the mixture is dispensed into the LED mold or placed onto the LED to fabricate the QD–LEDs, which is known as the packaging process. In this process, the compatibility of QDs’ surface ligands with the polymer matrix should be ensured, otherwise the poor compatibility can lead to agglomeration or surface damage of QDs. Besides, combination of QDs–polymer with LED chip is a key step that converts part of blue light into other wavelengths (WLs) of light, so as to generate white light in the end. Since QD-LEDs consist of three or more kinds of QDs, the spectra distribution should be optimized to achieve a high color-rendering ability. This requires both theoretical spectra optimization and experimental validation. In addition, to prolong the reliability and lifetime of QD-LEDs, QDs have to be protected from oxygen and moisture penetration. And the heat generation inside the package should be well controlled because high temperature results in QDs’ thermal quenching, consequently deteriorates QD-LEDs’ performance greatly. Overall, QD-LEDs’ packaging and applications present the abovementioned technical challenges. A profound and comprehensive understanding of these problems enables the advancements of QD-LEDs’ packaging processes and designs. In this review, we summarized the recent progress in the packaging of QD-LEDs. The wide applications of QD-LEDs in lighting and display were overviewed, followed by the challenges and the corresponding progresses for the QD-LEDs’ packaging. This is a domain in which significant progress has been achieved in the last decade, and reporting on these advances will facilitate state-of-the-art QD-LEDs’ packaging and application technologies. [DOI: 10.1115/1.4033143]
146 citations
TL;DR: A novel freeform lens was designed for simultaneous realization of LED uniform illumination and conformal phosphor coating, which can realize equivalent illumination uniformity, but the angular color uniformity can be enhanced by 282.3% when compared with the conventionalfreeform lens.
Abstract: A conformal phosphor coating can realize a phosphor layer with uniform thickness, which could enhance the angular color uniformity (ACU) of light-emitting diode (LED) packaging. In this study, a novel freeform lens was designed for simultaneous realization of LED uniform illumination and conformal phosphor coating. The detailed algorithm of the design method, which involves an extended light source and double refractions, was presented. The packaging configuration of the LED modules and the modeling of the light-conversion process were also presented. Monte Carlo ray-tracing simulations were conducted to validate the design method by comparisons with a conventional freeform lens. It is demonstrated that for the LED module with the present freeform lens, the illumination uniformity and ACU was 0.89 and 0.9283, respectively. The present freeform lens can realize equivalent illumination uniformity, but the angular color uniformity can be enhanced by 282.3% when compared with the conventional freeform lens.
99 citations
TL;DR: In this article, an optical-thermal coupling model was developed to predict the high phosphor temperature of LERP, and the critical incident power against thermal quenching under various factors was systematically studied.
96 citations
Cites methods from "Measurement and numerical studies o..."
...The absorption and scattering coefficient of phosphor particles toward blue and yellow light were calculated based on the Mie–Lorenz theory [29]....
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TL;DR: In this paper, the light extraction efficiency, correlated color temperature (CCT), and angular color uniformity (ACU) of the conformal coating was investigated by Monte Carlo ray-tracing simulations.
Abstract: The light extraction efficiency (LEE), correlated color temperature (CCT), and angular color uniformity (ACU) of the conformal coating phosphor silicone gel were investigated by Monte Carlo ray-tracing simulations. Relative to the conventional dispensing method, the conformal coating method can make the light-emitting diode (LED) module obtain better optical properties. It was found that the thickness of the phosphor layer in conformal coating was a key factor determining the optical performance. The thickness could be optimized for good optical properties. The optimal thickness is around 50-70 μm when taking LEE, CCT, and ACU into consideration.
79 citations
Cites methods from "Measurement and numerical studies o..."
...As for conventional dispensing method, the phosphor layer could be modelled as a spherical cap with the same amount of phosphor silicone gel as that in conformal coating method [17]....
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References
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01 Jan 1983
TL;DR: In this paper, a Potpourri of Particles is used to describe surface modes in small Particles and the Angular Dependence of Scattering is shown to be a function of the size of the particles.
Abstract: BASIC THEORY. Electromagnetic Theory. Absorption and Scattering by an Arbitrary Particle. Absorption and Scattering by a Sphere. Particles Small Compared with the Wavelength. Rayleigh--Gans Theory. Geometrical Optics. A Potpourri of Particles. OPTICAL PROPERTIES OF BULK MATTER. Classical Theories of Optical Constants. Measured Optical Properties. OPTICAL PROPERTIES OF PARTICLES. Extinction. Surface Modes in Small Particles. Angular Dependence of Scattering. A Miscellany of Applications. Appendices. References. Index.
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TL;DR: This IEEE Classic Reissue presents a unified introduction to the fundamental theories and applications of wave propagation and scattering in random media and is expressly designed for engineers and scientists who have an interest in optical, microwave, or acoustic wave propagate and scattering.
Abstract: A volume in the IEEE/OUP Series on Electromagnetic Wave Theory Donald G. Dudley, Series Editor This IEEE Classic Reissue presents a unified introduction to the fundamental theories and applications of wave propagation and scattering in random media. Now for the first time, the two volumes of Wave Propagation and Scattering in Random Media previously published by Academic Press in 1978 are combined into one comprehensive volume. This book presents a clear picture of how waves interact with the atmosphere, terrain, ocean, turbulence, aerosols, rain, snow, biological tissues, composite material, and other media. The theories presented will enable you to solve a variety of problems relating to clutter, interference, imaging, object detection, and communication theory for various media. This book is expressly designed for engineers and scientists who have an interest in optical, microwave, or acoustic wave propagation and scattering. Topics covered include:
5,877 citations
Additional excerpts
...According to the Lambert–Beer law [28,43,44], I 1⁄4 I0 expð−μextzÞ; ð20Þ...
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...μext normally has a relation with μabs and μsca as [44]...
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21 Mar 1997
TL;DR: The physics of gallium nitrides and related compounds GaN growth p-Type GaN obtained by electron beam irradiation n-Type GAN p-type GaN InGaN Zn and Si co-doped GaN double-heterostructure blue and blue green LEDs inGaN single-quantum-well structure LEDs room-temperature pulsed operation of laser diodes emission mechanisms of LEDs and LDs room temperature CW operation of InGAN MQW LDs latest results as discussed by the authors.
Abstract: Physics of gallium nitrides and related compounds GaN growth p-Type GaN obtained by electron beam irradiation n-Type GaN p-Type GaN InGaN Zn and Si co-doped InGaN/AlGaN double-heterostructure blue and blue-green LEDs inGaN single-quantum-well structure LEDs room-temperature pulsed operation of laser diodes emission mechanisms of LEDs and LDs room temperature CW operation of InGaN MQW LDs latest results - lasers with self-organized InGaN quantum dots
3,805 citations
"Measurement and numerical studies o..." refers background in this paper
...This promotes the rapid development of phosphor materials, including Ce3þ-doped garnet materials [8] and Eu2þ-activated nitride and silicate compounds [9–11]....
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TL;DR: The high efficiency of solid-state sources already provides energy savings and environmental benefits in a number of applications, but these sources also offer controllability of their spectral power distribution, spatial distribution, color temperature, temporal modulation, and polarization properties.
Abstract: More than a century after the introduction of incandescent lighting and half a century after the introduction of fluorescent lighting, solid-state light sources are revolutionizing an increasing number of applications. Whereas the efficiency of conventional incandescent and fluorescent lights is limited by fundamental factors that cannot be overcome, the efficiency of solid-state sources is limited only by human creativity and imagination. The high efficiency of solid-state sources already provides energy savings and environmental benefits in a number of applications. However, solid-state sources also offer controllability of their spectral power distribution, spatial distribution, color temperature, temporal modulation, and polarization properties. Such ‘‘smart’’ light sources can adjust to specific environments and requirements, a property that could result in tremendous benefits in lighting, automobiles, transportation, communication, imaging, agriculture, and medicine.
3,164 citations
TL;DR: In this paper, the status and future outlook of III-V compound semiconductor visible-spectrum light-emitting diodes (LEDs) are presented and light extraction techniques are reviewed.
Abstract: Status and future outlook of III-V compound semiconductor visible-spectrum light-emitting diodes (LEDs) are presented. Light extraction techniques are reviewed and extraction efficiencies are quantified in the 60%+ (AlGaInP) and ~80% (InGaN) regimes for state-of-the-art devices. The phosphor-based white LED concept is reviewed and recent performance discussed, showing that high-power white LEDs now approach the 100-lm/W regime. Devices employing multiple phosphors for "warm" white color temperatures (~3000-4000 K) and high color rendering (CRI>80), which provide properties critical for many illumination applications, are discussed. Recent developments in chip design, packaging, and high current performance lead to very high luminance devices (~50 Mcd/m2 white at 1 A forward current in 1times1 mm2 chip) that are suitable for application to automotive forward lighting. A prognosis for future LED performance levels is considered given further improvements in internal quantum efficiency, which to date lag achievements in light extraction efficiency for InGaN LEDs
1,882 citations