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- Front Matter: Volume 7784
- Alternative Design I
- Solid State Lighting and OLEDs Plenary Session
- OLEDs and SSL: Joint Session with Conference 7776
- Growth II
- Alternative Design II
- Phosphors
- Application I
- Growth III
- Application II
- Poster Session
Front Matter: Volume 7784
Front Matter: Volume 7784
Show abstract
This PDF file contains the front matter associated with SPIE Proceedings Volume 7784, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.
Alternative Design I
High-efficiency photonic quasi-crystal light emitting diodes incorporating buried photonic crystal structures
Show abstract
In this paper we investigate the utilization of a patterned photonic crystal layer positioned below the Multiple
Quantum Well region of a p-side up LED to improve light extraction and investigate the benefit of adding additional top
surface photonic crystal patterning to the same device. Performance for each design is evaluated in terms of angular
extraction efficiency and far field angular beam profile for fixed lattice geometry and a range of etch depths. We show
that a buried photonic crystal lattice improves extraction for emission angles below the critical angle for total internal
reflection, and does not have a detrimental effect over the normal extraction cone of the LED. An improvement of (33%
to 57% in extraction efficiency is obtained using a buried photonic crystal lattice alone. The introduction of additional
top surface patterning has potential to further improve the extraction efficiency up to 73%, and to tailor the shape of the
emission profile.
Energy efficient control of polychromatic solid state lighting using a sensor network
Show abstract
Motivated by opportunities in smart lighting, energy efficiency, and ubiquitous sensing, we present the design
of polychromatic solid-state lighting controlled using a sensor network. We developed both a spectrally tunable
light source and an interactive lighting testbed to study the effects of systems that adjust in response to changing
environmental lighting conditions and users' requirements of color and intensity. Using both linear and nonlinear
optimization, the setpoints of overdetermined systems (greater than three wavelengths) and the energy consumption
of the network are adjusted according to the room's lighting conditions (e.g., lux and color temperature of
multiple fixtures). Using these techniques, it is possible to maximize luminous efficacy or the color rendering
index for a given intensity and color temperature. We detail the system modeling, design, optical calibration,
and control theory required to modulate the luminous output and minimize wasted energy.
Estimating the junction temperature of AC LEDs
Yi-wei Liu,
Asiri Jayawardena,
Terence R. Klein,
et al.
Show abstract
Light-emitting diodes operating on alternating current are gaining popularity in the LED industry, especially for lighting
applications. Because junction temperature is a good predictor of LED performance, the availability of a method to
accurately estimate the junction temperature of AC LEDs would be very useful. This study investigated a method in
which a low reference current having a pulse width of less than several milliseconds was applied and the corresponding
voltage across the device was measured and correlated to the junction temperature. Laboratory experiment data showed
that the proposed method is a promising candidate for estimating AC LED junction temperature.
Solid State Lighting and OLEDs Plenary Session
What would Edison do with solid state lighting?
Show abstract
Thomas Edison is widely regarded as the greatest inventor in history and the most prominent individual behind the invention of the electric light. His impressive characteristics as an individual that led to his amazing success as an innovator continue to be an inspiration for researchers today. This paper considers how Edison might proceed in developing solid state lighting into a technology capable of displacing incumbent light sources, including his own incandescent lamps, then reviews some of the "Edison-like" contributions made to solid state lighting by the Next Generation Lighting research program at Georgia Tech.
OLEDs and SSL: Joint Session with Conference 7776
Nano-patterning for LED light extraction and for nanorod LED array formation
L. Y. Chen,
Y. Y. Huang,
C. S. Cheng,
et al.
Show abstract
Natural lithography is realized by spin-coating of nanoparticles. The surface textured LED s and
nanorod structured LEDs have been made successfully. Concentrated radiation profiles of nanorod structured and surface
textured LED are both observed. We fabricate these nano-structure by nature lithography method which use silica
nanosphere as etching mask. The SiO2 grown by PECVD is used as a space layer to realize the nanorod LED.
Furthermore, we suggest a light guided concept of the highly concentrated phenomena. The highest output power density
of nanorod LEDs is achieved. The reversed current of nanorod LEDs is also reduced down to nA level.
Growth II
A comprehensive study on the parameters effecting color conversion in phosphor converted white light emitting diodes
Show abstract
Due to the light scattering processes that take place within the color conversion elements (CCE) of phosphor converted
light-emitting diodes (LEDs) and the rather different emission characteristics of the blue LED and the converted light,
which have to be matched by the scattering processes, a better understanding of the underlying physical aspects is
indispensable for device optimization. We give, based on optical ray-tracing, a comprehensive survey on the parameters
that effect color conversion and light scattering within the CCEs of phosphor converted LEDs. Studies range from
variations of the geometrical (height, width) to the compositional (concentration of the phosphor in the matrix material,
differences of the refractive indices of the matrix and the phosphor materials, phosphor particle size) parameters and
identify their respective impacts on the color temperatures and the luminous efficacies of the respective LEDs.
Free-standing GaN-based LEDs with ALD-Al2O3/Si substrate removed by wet etching
Show abstract
High quality InGaN-based LEDs have been grown on Si (111) substrates using an Al2O3 transition layer. Freestanding,
fabricated LED devices were achieved by removing the Si substrate using selective area wet etching.
Conventional device design was used for LED fabrication, in which p-type and n-type contacts are located at the same
side of the epilayers. These LED devices were bonded to a dual in-line package (DIP), and epoxy was used to protect the
front side of the epilayers thin films as well as the bonding wires. The Si substrate was removed by wet etching while the
chip was mounted in the DIP which prevented the thin film from cracking or warping.
Electroluminescence (EL) characteristics of the LED devices grown on ALD/Si were measured before and after
substrate removal. No significant change in peak emission wavelength was observed, nor any change in EL intensity
versus drive current. No degradation of electrical and optical properties was observed. This indicates that the devices
were not damaged by the wet etching process. However, the luminescence intensity of devices both before and after wet
etching did not increase beyond a drive current of ~60 mA due to inefficient heat dissipation. The process developed
and the challenges involved in the larger area substrate removal process will be discussed which could be substantially
beneficial to the future substrate transfer and packaging in the industrial fabrication of LED on silicon substrate.
Reactor pressure: growth temperature relation for InN epilayers grown by high-pressure CVD
Show abstract
Results on the achievable growth temperature as a function of the reactor pressure for the growth of InN by high-pressure CVD are presented. As the reactor pressure was increased from 1 bar to 19 bar, the optimal growth temperature raised from 759°C to 876°C, an increase of 6.6 °C/bar. The InN layers were grown in a horizontal flow channel reactor, using a pulsed precursor injection scheme. The structural and optical properties of the epilayers have been investigated by Raman spectroscopy, X-ray diffraction, and IR reflectance spectroscopy.
Broad area side emission LED for high power application
Show abstract
Larger chip size with higher injection current is used in high power and high brightness LEDs. Thermal management and
good current spreading are critical issues in these high power applications, besides the requirement on higher internal and
external quantum efficiency. The conventional top emitting configuration is not suitable because of the poor thermal
conductivity of the sapphire substrate and poor light extraction efficiency. The substrate removal and flip-chip methods
can provide much better heat dissipation but having concerns on the yield. In this paper, we reported a broad area side
emission LEDs (BSLED) with a large length to width ratio of 5000um to 500um so as to have a comparable light
emitting area with top/back emission LEDs in the same amount of GaN wafer area. Both top and backside of wafer are
coated with metals as mirror reflectors and are attached to heat sinks for better heat dissipation. The L-I, I-V and
polarization characteristics from fabricated BSLED showed it is more promising than conventional top emitting LED at
the same size. The BSLED provides more flexibility in lighting device design and could be more suitable for certain
application like LCD backlighting.
Optical, structural properties and experimental procedures of GaGdN grown by metalorganic chemical vapor deposition
Show abstract
Rare earth (RE) elements are promising alternatives to transition metals (TMs) for use in developing a dilute
magnetic semiconductor (DMS) for spintronics applications. Instead of relying on the d-shell electrons of the TMs as the
magnetic element, the 4f electrons from the RE elements are used. The 4f RE elements can have larger magnetic
moments as compared to 3d TMs, because the 4f orbits are localized and the direct coupling between the 4f ions is weak.
There have been several reports of using RE elements for optoelectronic applications, as their various internal f-shell
electronic transitions vary in energy from infrared to visible.
Alternative Design II
Physical constraints on the performance of LED lamp replacements for A-19, PAR-38 and MR-16 configurations
Show abstract
Since the introduction of LED technology into the general illumination lighting market, one desired feature has been the
ability to replace the luminaire lamp in a similar manner to conventional sources (e.g. screw or plug in). Due to thermal
management issues, successfully implementing this feature has proven difficult with many manufacturers simply
integrating the LED sources into the luminaire. However, there are LED replacement lamp products on the market that
manufacturers claim to be the equivalent of their conventional source counterparts. This paper will examine the
relationships between lifetime, light output, source efficacy, thermal management and physical size for three common
lamps: the MR-16, the A-19 (standard incandescent shape) and the PAR-38 (standard floodlight shape). The author will
evaluate the physical size envelope for the three lamp types. Next, a theoretical model for maximum thermal dissipation
to ambient will be determined. Then using data from LED manufacturers, junction temperature limits versus lifetime
will be evaluated and used to determine maximum input power. This input power limit combined with manufacturer's
data and assumed optical and electrical losses will be used to evaluate potential light output of the lamp and compared to
conventional lamp outputs. Upper limits for light output will be determined.
Solid state lighting in buildings: status and future
Show abstract
In recent years, there has been considerable press coverage about the promise of Solid State Lighting (SSL). Despite this
or perhaps because of the coverage, it can be difficult to separate hype from reality and set expectations for the near to
medium term. The short answer is there are good SSL products on the market now and some poor ones. The good ones
are getting better, more common, and more affordable. This paper will cover the basics of the key components that make
up a luminaire which are LEDs (light emitting diode), power supply, optics, and thermo/mechanical subsystems. Each
component will be reviewed with highlights as to what is important. These subsystems will then be considered as a
system. Several methodologies for designing both spot and area luminaires will be discussed focusing on non-residential
buildings. The topic of SSL lifetime will be discussed. Finally, trends will be explored to provide an understanding of the
kinds of improvements one can expect and the timeframe over which they may occur.
Application efficacy for comparing energy demand in lighting applications
Show abstract
The light-emitting diode (LED) is a rapidly evolving, energy-efficient light source technology that holds promise to
address the increasing need for energy conservation. However, the common belief that a high-efficacy light source
equates to lower energy demand in application is incorrect. Generally, when a new light source technology replaces an
existing light source in an application and claims energy savings, the inherent assumption is that all of the requirements
of the application are met. In the case of directional lighting applications, what matters ultimately is the amount of
luminous flux illuminating the task area. Therefore, when quantifying the performance of a luminaire, ideally one must
consider only the amount of flux reaching the task area and the total power demanded.
The objective of this paper is to introduce an alternative concept, application efficacy. This paper will demonstrate the
concept's usefulness and proposed metrics for three different lighting applications-under-cabinet task lighting,
refrigerated display case lighting, and outdoor parking lot lighting-and show how it better relates to energy demand.
Details of laboratory experiments and software analysis along with data are presented for the three applications.
Advanced dimming strategy for solid state luminaires
Show abstract
Increased luminaire gamut as well as increase in luminous efficiency is found when the LED based luminaire is driven
by a hybrid PWM/AM dimming technique. This technique is applicable to any n-chromaticity luminaire but it is especially
suitable for trichromatic RGB luminaires that do not have inherent degrees of freedom. Diodes' properties under
the hybrid dimming method were measured and used in nonlinear optimization routine to find the driving conditions that
yield e.g. the highest possible efficacy for a given color point.
Phosphors
Post-synthesis annealing effects on SrGa2Se4:Eu2+ phosphors with peak emission wavelength in the green gap
Show abstract
A high-quality white light source requires high luminous efficacy (lumens per input watt). Theoretically, in the "greenyellow"
spectral region (with a peak wavelength at around 555 nm), the luminous efficiency (lumens per radiant watt)
reaches a maximum based on the luminous efficiency function, V(λ), and can potentially generate high luminous
efficacy. Unfortunately, the light-emitting diode (LED) suffers from low external quantum efficiency in the "greenyellow"
region, thereby lowering the luminous efficacy value. Researchers have sought solutions such as nonpolar or
semipolar InGaN/GaN LEDs. An alternative to generating green light is to use phosphor down-conversion by exciting a
green emission phosphor with a near-UV or blue LED of higher external quantum efficiency. In this study, a
SrGa2Se4:Eu2+ phosphor with peak emission wavelength at 555 nm was initially synthesized and followed by a
systematic study of the post-synthesis annealing. The purpose of this study was to investigate how post-synthesis
annealing conditions, including annealing temperature, annealing duration, and annealing ambient atmosphere, can
affect phosphor performance. The phosphor performance was characterized in terms of external quantum efficiency and
emission properties. How the external quantum efficiency of the phosphor can be further improved is also discussed.
Application I
Philips' 2nd generation Novallure LED candle lamp
Show abstract
Finding an energy efficient replacement of incandescent candle lamp has been a technical challenge. Compact
fluorescent lamps, for example, can be miniaturized to fit the form factor of a candle lamp but they fail to reproduce its
"sparkle" effect. Empowered by solid state lighting technology along with original optical design, Philips has
successfully developed LED-powered candle lamps "Novallure" with great energy savings (2W power consumption with
lumen output of 55 lumen) and the "butterfly" radiation pattern that mimics the sparkle effect from an incandescent
candle lamp. With new high performance LED packages, novel under-cut prismatic optics and state-of-the-art electronic
driver solution and thermal solution, we have developed a 2nd generation Novallure with breakthrough performance: a
dimmable 2700K 136 lumen LED candle lamp with CRI 90.
Thermal transient characteristics of flip chip high power light emitting diodes
Show abstract
The die-attached quality and the thermal transient characteristics of high power flip chip light emitting diodes (LEDs)
are investigated using thermal transient tester. Various die-attached materials were utilized to compare the difference in
their thermal resistances and long term performance. By applying accelerated aging stress, the deterioration rates at the
die-attached layers were obtained. Numerical simulation provided further understanding of LED device temperature
distribution and also revealed that the thermal variance at the die-attached interface can be recognized within only few
milliseconds for the flip chip structure. The effects of bump arrangement and material were analyzed to achieve high
temperature uniformity and low thermal resistance for high power LEDs.
LED luminaire longevity strategy models comparison
Show abstract
As energy efficiency becomes more and more important, light-emitting diodes (LEDs) are a promising alternative to
traditional lighting. Indeed, the energy efficiency of LEDs is still improving as their luminosity is modulated by current.
Moreover, for applications such as exterior lamp posts, their small size, directionality, colors and high frequency
response allow to combine them and provide design possibilities which are impossible with any other light source.
However, as any lamp, LEDs have a lumen depreciation which is a function of both current and temperature. Thus, to
take advantage of the full characteristics of LEDs, LED luminaire longevity strategies must be carefully studied and
planned, especially since the IES and CIE guidelines state clearly that the luminaire must maintain the rated
recommended light level until the end of the system's operating life. The recommended approach for LED luminaire
specification is therefore to use the end-of-life light level when evaluating the luminaire. Different power supply
strategies have been simulated to determine which one maximizes energy saving and lifetime. With these results, it
appears that active control can save at least 25% in energy, but the best strategy cannot be determined because of
uncertainties in luminosity degradation models.
A two-metric proposal to specify the color-rendering properties of light sources for retail lighting
Show abstract
Lighting plays an important role in supporting retail operations, from attracting customers, to enabling the evaluation of
merchandise, to facilitating the completion of the sale. Lighting also contributes to the identity, comfort, and visual
quality of a retail store. With the increasing availability and quality of white LEDs, retail lighting specifiers are now
considering LED lighting in stores. The color rendering of light sources is a key factor in supporting retail lighting goals
and thus influences a light source's acceptance by users and specifiers. However, there is limited information on what
consumers' color preferences are, and metrics used to describe the color properties of light sources often are equivocal
and fail to predict preference. The color rendering of light sources is described in the industry solely by the color
rendering index (CRI), which is only indirectly related to human perception. CRI is intended to characterize the
appearance of objects illuminated by the source and is increasingly being challenged because new sources are being
developed with increasingly exotic spectral power distributions. This paper discusses how CRI might be augmented to
better use it in support of the design objectives for retail merchandising. The proposed guidelines include the use of
gamut area index as a complementary metric to CRI for assuring good color rendering.
Growth III
Fully phosphor-converted LEDs with Lumiramic phosphor technology
Show abstract
Fully phosphor-converted LEDs (FpcLeds) with saturated emission have been realized in the green and amber spectral
region. With the Lumiramic phosphor technology it is possible to achieve high package efficiency with minimum
transmission of blue light from the primary LED source. This is done by keeping the scattering properties of the
phosphor layer low while the phosphor thickness is chosen to fully convert all blue LED emission. It is shown that this
can be done not only for optically isotropic Lumiramic materials like garnets, but also for oxonitridosilicate materials
like the green emitting Europium doped SrSi2O2N2, crystallizing in a triclinic lattice with three optical axes. The
scattering power of the Lumiramic can be decreased to acceptable levels by increasing the size of the crystallites in the
densely sintered ceramics. Light propagation is found to be described well with Mie scattering of mono-sized SrSi2O2N2
spheres with refraction index differing by 0.07 to the refractive index of a SrSi2O2N2 matrix material. Using this
technology, the green-yellow gap of visible light emitting LEDs can be bridged and color tunable lamps with the
efficiency and flux of today's white phosphor-converted LEDs become feasible.
High brightness GaN light emitting diodes with different barrier widths in quantum wells for general lighting application
Show abstract
High brightness InGaN/GaN multiple quantum well structures have been grown on sapphire substrates by
metalorganic chemical vapor deposition, for wide range visible light emitting diode application. The compositions and
sizes within quantum wells were designed according to the requirements on the LED performance. Samples were
investigated by a variety of characterization techniques. Optimization of the growth parameters and process was realized
and evidenced by high resolution X-ray diffraction measurements. Optical spectroscopic properties were further studied
and quantum confined stokes shift was observed from room temperature and low temperature photoluminescence as well
as time resolved photoluminescence measurements.
The effects of titania diffuser on angular color homogeneity in the phosphor conformal coated white LEDs
Show abstract
White light-emitting diodes (LEDs) have dramatically developed and gradually taken over from the conventional light
source as the solid-state lighting during the last decade. It is now sufficient for illumination application in performance,
while it is still insufficient in color quality. Especially, most of phosphor-converted white LEDs have the poor angular
color homogeneity. In this study, we adopted a distinctive phosphor conformal coating technique in the packaging
process to reduce the variance of correlated color temperature (CCT) among the packages and spatial CCT in the
package. Also, to reduce the spatial CCT variance without considerable shrinkage of luminous efficacy, we applied submicrometer
scale TiO2 powder as diffuser in the phosphor layer or in the encapsulation layer of white LED with a
phosphor conformal coating layer and investigated the effects of titania diffuser on angular color homogeneity and
optical performance. Regardless of the diffuser content, spatial CCT variance and luminous efficacy were decreased with
the increase of the diffuser content. Nevertheless, among the conditions for achievement of the equivalent in color
uniformity, the luminous efficacy in the case of 0.1 wt% diffuser mingled in the encapsulation layer was 20 % higher
than in the case of 5 wt% diffuser mingled in the phosphor layer. These phenomena result from differences of light
scattering loss caused by 10 times more volume of diffuser mixed in the phosphor layer than in the encapsulation layer.
Application II
Concepts for future solid state lighting solutions
Show abstract
In this contribution the relevant technological aspects of LED-based lamps for solid state lighting are discussed. In
addition to general energy efficiency considerations improvements in LED chip technology and white light generation
are presented.
Emerging standard for thermal testing of power LEDs and its possible implementation
András Poppe,
Gábor Farkas,
Gábor Molnár,
et al.
Show abstract
Nowadays the demand for thermal standards for power LEDs is increasing. On one hand metrics for fair comparison of
competing products are needed; on the other hand, designers of power LED-based applications need reliable and
meaningful data for their daily work. Today's data sheet information does hardly meet any of these requirements. In 2008
the JEDEC JC15 committee on thermal standardization of semiconductor devices decided to take action and created a
task group to deal with thermal standardization issues of power LEDs. CIE has also created two new technical
committees (TC2-63, TC2-64) which also aim to address thermal issues during measurement of high brightness / high
power LEDs. This paper deals with thermal issues that are specific to light emitting diodes by describing novel test
methods which may form basis of new measurement guidelines or standards including combined thermal and
radiometric measurement of LEDs. Thermal issues in connection with short pulse measurements of LEDs and some
thermal aspects of LM80 tests are also discussed.
Poster Session
Optical, structural, and nuclear scientific studies of AlGaN with high Al composition
Tse Yang Lin,
Yee Ling Chung,
Lin Li,
et al.
Show abstract
AlGaN epilayers with higher Al-compositions were grown by Metalorganic Chemical Vapor Deposition (MOCVD)
on (0001) sapphire. Trimethylgallium (TMGa), trimethylaluminium (TMAl) and NH3 were used as the source precursors
for Ga, Al, and N, respectively. A 25 nm AlN nucleation layer was first grown at low-temperature of 590 °C at 300 Torr.
Followed, AlxGa1-xN layers were grown at 1080 °C on low-temperature AlN nucleation layers.
The heterostructures were characterized by a series of techniques, including x-ray diffraction (XRD), Rutherford
backscattering (RBS), photoluminescence (PL), scanning electron microscopy (SEM) and Raman scattering. Precise Al
compositions were determined through XRD, RBS, and SEM combined measurements. Room Temperature Raman
Scattering spectra shows three major bands from AlGaN alloys, which are AlN-like, A1 longitudinal optical (LO) phonon
modes, and E2 transverse optical (TO) band, respectively, plus several peak comes from the substrate. Raman spectral
line shape analysis lead to an optical determination of the electrical property free carrier concentration of AlGaN. The
optical properties of AlGaN with high Al composition were presented here.
Rutherford backscattering and optical studies for ZnO thin films on sapphire substrates grown by metalorganic chemical vapor deposition
Yee Ling Chung,
Lin Li,
Shude Yao,
et al.
Show abstract
A series of ZnO thin films with different thicknesses grown on sapphire substrates by metalorganic chemical vapor
deposition (MOCVD) have been studied by different characterization techniques. The optical properties are investigated
by photoluminescence (PL), optical transmission (OT) and 1st order derivatives, various angle scanning ellipsometry
(VASE). Rutherford Backscattering (RBS) shows the atomic Zn:O ratios with a few percentage aviation from 1:1, and
thicknesses in range of 10~230 nm, roughness layer with 10~30nm, which are corresponding to results from atomic force
microscopy (AFM), and scanning electron microscopy (SEM). The optical and structure characterization measurements
have confirmed the good quality of these epitaxial ZnO materials.
A nanorods AlN layer prepared by sputtering at oblique-angle and application as a buffer layer in a GaN-based light emitting diodes
Show abstract
We presents a nanorods AlN films on sapphire substrate deposited at oblique-angle by a radio-frequency reactive
magnetron sputtering. A nanorods AlN layer was employed as a buffer layer for a GaN-based LEDs to improve
optoelectronic characteristics of LEDs. The diameter of the nanorods AlN buffer layer is in the range of 30-50 nm.
Typical current-voltage characteristics of the GaN-based LEDs with a nanorods AlN buffer layer have a forward-bias
voltage of 3.1 V at an injection current of 20 mA. The output intensity of LEDs initially increases linearly as the
injection current increases from 10 mA to 150 mA. The light output power of the GaN-based LED with a nanoporous
AlN layer was about 31% higher than that of a GaN-based LED without a nanoporous AlN layer at an injection current
of 250 mA.
Effects of color temperature and luminous efficiency for RGB LEDs mixing with tuning voltage
Show abstract
LEDs are already being used in monitors, and they have more recently appeared in plate displays. Therefore, this study investigated the effects of color temperature and luminous efficiency for RGB LEDs mixing with tuning voltage. The base voltages of red, green, and blue LEDs will be set up for the color temperature of 6500K(D65 white light). These results exhibited that changing the voltage of red LED had the broader color temperature from 2000 K to 16000 K and low luminous variation from 27 to 40 lm /W than green and blue LEDs. Though the green LED had the low luminous variation from 25 to 40 lm /W but the color temperature only tuned from 2500K to 7500K. In contrast, though the blue LED had large color temperature from 4000K to 19000K but the luminous efficiency had rapid variation from 20 to 40 lm /W. The green LED was suitable for fine-tuning color temperature from 2500K to 7500K. The blue LED had rapid variation of color temperature from 4000K to 19000K so it could only suitable for high-color temperature modulation. The color shifts (Δuv) of red and green LEDs were the same variation with color temperature but not for blue LED.
Assessment of ESD robustness in high power light emitting diodes
Shih-Chun Yang,
Pang Lin,
Han-Kuei Fu,
et al.
Show abstract
The capability of high-power nitride-based light-emitting diodes (HPLED) to withstand electrostatic discharge
(ESD) is very important key index due to the horizontal structure of the insulating property of the sapphire substrate.
However, it is difficult to real-time monitor the damage caused by the ESD stress because it occurred in a very short
period. Current-voltage (I-V) curves and electroluminescence (EL) spectrum were applied to study the change during the
series ESD stress. Time-resolved optical beam induced current (TR-OBIC) was used to analyze the characteristics of the
delay time between normal region and the defect point caused by ESD stress. Transmission electron microscopy (TEM)
was used to compare to the difference in the distribution of damage region and investigate the failure modes. During the
series ESD stresses, V-shaped pits suffered from the high electrical field and the distance from multi-quantum well
(MQW). The bottom of V-shaped defect would be one of index to assess the ESD endurance of LED chips.
Effects of radiation characteristic and luminous efficiency for LED lampshade with cylindrical lens
Show abstract
Light emitting diode (LED) is an environmental-friendly product and could be a main lighting source in future. The
research was to design a suitable LED lampshade for the street lighting. The radiation characteristic was required to be a
rectangular distribution at the divergence-angle ratio of 7:3 for the x and y directions. Hence a design of two cylindrical
lenses on the lampshade was used for the lighting distribution. Then an optimal simulation of these curvatures was done
for the luminous distribution and efficiency. Final we got a rectangular lighting of the divergence-angle ratio of 7:3 and
the radiator characteristic of bat-wing. The tolerance analyses of LED source distances were done on the x, y and z
directions. The z direction was more sensibility than x and y directions for luminous efficiency and its tolerance must be
kept under ±0.5mm for the illumination efficiency to be over 95%. Anyway, the similar extent could reach to 98.46% by
Normalized Cross Correlation (NCC) between experimental and simulation and the error extent could reduce to 6.87%
by Root Mean Square (RMS) error mode. The total luminance efficiency could reach to 92% without AR coating.
Luminescence studies of BaGd2O4: Tb+3 phosphor
Show abstract
The polycrystalline BaGd2-xO4: Tbx (x = 0.00 - 0.10) phosphors have been prepared by conventional high temperature
solid state reaction method. All the prepared samples were characterized by powder XRD and EDS techniques. The
photoluminescence (PL) and thermally stimulated luminescence (TSL) studies of these materials were investigated. For
PL studies the samples were excited with 263 nm UV light. All the samples showed strong green emission at 543 nm
due to 5D4→7F5 transition of Tb3+ ions. PL peak intensity was found to increase with increasing dopant concentration.
For TSL studies, these samples were γ-irradiated with different dose rates using 60Co source. TSL of these phosphors
showed a sharp glow peak with peak maxima at 394 K. It is found that the incorporation of terbium activator in
BaGd2O4 host lattice resulted in the increase of TSL intensity. The luminescence results of these materials shows that
these are promising candidates for new green emission phosphor.