InGaN/GaN blue light emitting diodes with varied quantum well thickness from 2.4 nm to 3.6 nm are fabricated and characterized by atmosphere pressure metalorganic chemical vapor deposition (AP-MOCVD). Experimental results show that the exciton localization effect is enhanced from 21.76 to 23.48 by increasing the quantum well thickness from 2.4 nm to 2.7 nm. However, with the further increase of quantum well thickness, the exciton localization effect becomes weaker. Meanwhile, the peak wavelength of electroluminescence redshift with the increase of well thickness due to the larger quantum confined Stark effect (QCSE). In addition, the efficiency droop can be improved by increasing the well thickness.

Blue LED progress has laid the ground works of nitride technology to tackle the higher challenge of longer wavelength direct emitters of green, yellow, and orange. Use of bulk GaN substrate allows leapfrogging epitaxy development and offers crystallographic planes that allow higher crystal perfection and a control over piezoelectric polarization. Their combination allows stabilization of emission wavelength with current. Further improvement is found in substrate patterning on the micro and nano-meter length scale where we find roughly equal performance enhancement due to both, enhancement in light extraction and enhanced crystalline perfection.

Lighting solutions with colored LEDs provide many opportunities for illumination. One of these opportunities is to create a color tunable light source. In this way different kinds of white light (color temperature) as well as discrete colors may be realized. This opens the field for applications as mood lighting. But there is always a spatial separation of the distinct LEDs that might get converted into an angular separation by any collimating optics. This angular separation causes such problems like color fringes and colored shadows that cannot be accepted in most applications. Conventional methods to solve these problems include e.g. mixing rods or dichroic filters. A new approach is the use of the dispersive effect of a diffractive structure to compensate the angular separation of the different colors. In this contribution the potential and limitations of diffractive structures in LED color mixing applications are discussed. Ray tracing simulations were performed to analyze such important parameters like efficiency, color performance and the cross section of the color mixing optics. New means for the estimation of color mixing performance were developed. A software tool makes it possible to detect the color distribution within ray trace data and it provides a quality factor to estimate the color mixing performance. It can be shown that the spectral band width has a large influence on the mixing process. Ray tracing simulations are compared with results of an experimental setup such that both measured as well as simulated data is presented.

Organic Light Emitting Diode (OLED) technology is rapidly maturing to be ready for next generation of light source for general lighting. The current standard test methods for solid state lighting have evolved for semiconductor sources, with point-like emission characteristics. However, OLED devices are extended surface emitters, where spatial uniformity and angular variation of brightness and colour are important. This necessitates advanced test methods to obtain meaningful data for fundamental understanding, lighting product development and deployment. In this work, a near field imaging goniophotometer was used to characterize lighting-class white OLED devices, where luminance and colour information of the pixels on the light sources were measured at a near field distance for various angles. Analysis was performed to obtain angle dependent luminous intensity, CIE chromaticity coordinates and correlated colour temperature (CCT) in the far field. Furthermore, a complete ray set with chromaticity information was generated, so that illuminance at any distance and angle from the light source can be determined. The generated ray set is needed for optical modeling and design of OLED luminaires. Our results show that luminance non-uniformity could potentially affect the luminaire aesthetics and CCT can vary with angle by more than 2000K. This leads to the same source being perceived as warm or cool depending on the viewing angle. As OLEDs are becoming commercially available, this could be a major challenge for lighting designers. Near field measurement can provide detailed specifications and quantitative comparison between OLED products for performance improvement.

Nanostructures, like periodic arrays of scatters or low-index gratings, are used to improve the light outcoupling from organic light-emitting diodes (OLED). In order to optimize geometrical and material properties of such structures, simulations of the outcoupling process are very helpful. The finite element method is best suited for an accurate discretization of the geometry and the singular-like field profile within the structured layer and the emitting layer. However, a finite element simulation of the overall OLED stack is often beyond available computer resources. The main focus of this paper is the simulation of a single dipole source embedded into a twofold infinitely periodic OLED structure. To overcome the numerical burden we apply the Floquet transform, so that the computational domain reduces to the unit cell. The relevant outcoupling data are than gained by inverse Flouqet transforming. This step requires a careful numerical treatment as reported in this paper.

We have developed monolithic white light emitting diodes (LEDs) with a hybrid structure of planar c-planes and nano size hexagonal pyramids. The white spectrum is composed of blue and yellow emissions from the InGaN multi quantum wells (MQWs) on the planar c-planes and on the nano pyramids, respectively. The yellow emission is originated from quantum wells, wires, and dots that are formed at the sides, edges, and tops of the nano-pyramids, respectively. As a result, the emission peaks are different and the entire yellow spectrum is broad enough to make a white in combination with a blue emission. The longer wavelength from the InGaN on nano-pyramids than the wavelength from the InGaN on c-planes is explained by excess In supply from the dielectric selective growth mask. The color temperature is tuned from 3600K to 6400K by controlling the relative area ratio of c-plane and nano-pyramids.

The improvement of the performance and the reduction of the cost for LEDs using the moth-eye patterned sapphire substrate (MPSS) were investigated. TEM and CL observation results clearly show that the MPSS can provide a thinner GaN template of equal or higher quality than the micron scale patterned sapphire substrate (PSS) since the MPSS only has a submicron scale structure. A 3-μm-thick high quality GaN template on the MPSS with a dislocation density of 1.9×10⁸ cm^-2 has been demonstrated. The LEDs on MPSS with a 600 nm pitch show the highest light output among the evaluated LEDs on various types of substrates as it is 1.52 times higher than that on flat sapphire substrate (FSS) and 1.18 times higher than that on PSS. The pitch dependence of the light output improvement is in excellent agreement with that of the transmittance at GaN/sapphire interface simulated by the rigorous coupled wave analysis. As a result of comparisons for the GaN templates and LEDs on MPSS, PSS and FSS, it can be concluded that MPSS provides the most cost effective solution for high performance LED.

Quantum dot light-emitting diodes (QD-LEDs) have recently attracted much attention due to its highly saturated emission color and the capability of tuning the emission color by means of engineering its size. In this letter, an allinorganic light-emitting diode based on colloidal core/shell CdS/ZnS nanocrystal quantum dots (QDs) emissive layer sandwiched between p-type NiO and n-type ZnO is reported. NiO and ZnO layers are deposited by means of the lowcost spin coating technique. The device showed a rectification behavior and QD light emission with the electroluminescent emissions at 605nm.

The fabrication procedure of a moth-eye patterned sapphire substrate (MPSS), which can enhance the light extraction efficiency of nitride-based light emitting diodes (LEDs) has been examined. The optimization of surface morphology after the etching of the MPSS for high-quality GaN growth was also performed. Then, we fabricated MPSS samples with a fixed pitch of 460nm, and corn height ranging from 50 to 350nm. The light extraction efficiency of blue-LEDs grown on a series of MPSS was enhanced about 1.4 times compared with the devices grown on a flat sapphire substrate. We found that if corn height exceeds 150nm, the MPSS effect is sufficiently observed.

In this paper, we study the computational modeling of the localized surface plasmonic and scattering field effect arising from of gold nanorods. We also report the synthesis and optical characterization of core-spacer-shell nanocomposites composed of gold nanorods coated with SiO2 and finally coated with Y2O3:Er3+/Yb3+ (Aunanorods@mSiO2@Y2O3:Er3+/Yb) through a layer-by-layer method. Preliminary upconversion analysis of singly (Aunanorods@mSiO2@Y2O3:Er3+/Yb) at 980 excitation indicates that the composition has to be optimized to understand the role of silica as a spacer and near field enhancer (gold nanorod) in the system.

Nanowires (NWs)-based light emitting diodes (LEDs) have drawn large interest due to many advantages compared to thin film based devices. We have successfully prepared epitaxial n-ZnO(NW)/p-GaN heterojunctions using low temperature soft electrochemical techniques. The structures have been used in LED devices and exhibited highly interesting performances. Moreover, the bandgap of ZnO has been tuned by Cu or Cd doping at controlled atomic concentration. A result was the controlled shift of the LED emission in the visible spectral wavelength region. Using DFT computing calculations, we have also shown that the bandgap narrowing has two different origins for Zn_1-xCd_xO (ZnO:Cd) and ZnO:Cu. In the first case, it is due to the crystal lattice expansion, whereas in the second case Cu-3d donor and Cu-3d combined to O-2p acceptor bands appear in the bandgap which broadnesses increase with the dopant concentration. This leads to the bandgap reduction.

This paper proposes for the first time the preparation of n-InGaN/p-Si templates as substrates for InGaN device applications. By using MOVPE, a thick (~0.5 m) InGaN with an intermediate In composition has been successfully grown on Si(111) substrates using an AlN interlayer. By optimizing growth temperature and TMI/(TMI+TEG) molar ratio, InGaN films with In content up to 0.5 are successfully grown. Tensile stress in InGaN films grown at 700°C is estimated to be about half of that for GaN grown at 1100°C and no cracks are found in the InGaN layers. The films grown at a relatively high temperature (700-750°C) show phase separation when their thickness exceeds a critical value. Critical thickness for phase separation is larger for a film grown at a lower temperature with a high In content. For InGaN grown at 600°C with a thickness of 0.8 m, no phase separation is detected by both X-ray diffraction and PL. Such a low temperature-grown InGaN shows a large tilt fluctuation. Ohmic I-V characteristics are obtained between n-InGaN and p-Si and the resistance is markedly decreased with increasing In content in InGaN. The Si pn junction beneath the In0.42Ga0.58N layer behaves well as a solar cell with an InGaN filter. For both n-InGaN/p-Si, the presence of an AlN interlayer between the epilayer and the substrate does not have a significant contribution to the series resistance.

For LEDs with original structure and copper heat spreader, the highest surface temperatures of 3×3 array LEDs modules were 52.6 and 42.67 °C (with 1050 mA injection current), while the highest surface temperatures of 4×4 array LEDs modules were 58.55 and 48.85 °C (with 1400 mA injection current), respectively. As the 5×5 array LEDs modules with original structure and copper heat spreader were fabricated, the highest surface temperatures at 1750 mA injection current were 68.51 and 56.73 °C, respectively. The thermal resistance of optimal LEDs array module with copper heat spreader on heat sink using compound solder is reduced obviously. On the other hand, the output powers of 3×3, 4×4 and 5×5 array LEDs modules with original structure were 3621.7, 6346.3 and 9760.4 mW at injection currents of 1050, 1400 and 1750 mA, respectively. Meanwhile, the output powers of these samples with copper heat spreader can be improved to 4098.5, 7150.3 and 10919.6 mW, respectively. The optical and thermal characteristics of array LEDs module have been improved significantly using the cup-shaped copper structure. Furthermore, various types of epoxy-packaged LEDs with cup-shaped structure were also fabricated. It is found that the light extraction efficiency of LED with semicircle package has 55% improvement as compared to that of LED with flat package. The cup-shaped copper structure was contacted directly with sapphire to enhance heat dissipation. In addition to efficient heat dissipation, the light extraction of the lateral emitting in high-power LEDs can be improved.

The enhancement of light extraction efficiency for thin-film-flip-chip (TFFC) InGaN QWs LEDs with GaN microdomes on n-GaN layer was studied. The three dimensional FDTD method was used to calculate the light extraction efficiency for the TFFC InGaN QWs LEDs emitting at visible spectral regime, as compared to that of the conventional TFFC InGaN QWs LEDs. The calculation indicates significant dependence of the p-GaN layer thickness on the light extraction efficiency. Significant enhancement of the light extraction efficiency (2.5-2.7 times for λpeak=460nm and 2.7- 2.8 times for λpeak=550nm) is achievable from LEDs with GaN micro-domes with optimized micro-dome diameter and height.

High indium content InGaN films were grown on sapphire substrate using low temperature pulsed laser deposition (PLD) with nitrogen plasma and a specific target. The controllable target consists of two separate sections: an indium sheet with periodic rectangular-holes and a standard GaN wafer. By changing the rectangular-hole area, a modulated indium vapor was excited by pulsed laser and introduced into the InGaN deposition reaction, contributing the increase in the incorporation of indium into the InGaN film. The structural and optical stability of the 33 and 60% indium InGaN revealed no differences in the line-shape and peak position even after annealing at 800°C for 75 min from x-ray diffraction and luminescence results. Moreover, such high thermal stability of 60% InGaN film was put in metal organic chemical vapor deposition (MOCVD) to regrow GaN layer, the peak position of 860 nm remained unchanged after MOCVD regrowth. The flat and uniform of regrown sample indicates that the PLD method used in this study is indeed promising for the development long wavelength of high indium content InGaN emitters.

The rapid development in flux and efficiency of Light Emitting Diodes (LED) has resulted in a flooding of the lighting market with Solid State Lighting (SSL) products. Many traditional light sources can advantageously be replaced by SSL products. There are, however, large variations in the quality of these products, and some are not better than the ones they are supposed to replace. A lack of quality demands and standards makes it difficult for consumers to get an overview of the SSL products. Here the results of a two year study investigating SSL products on the Danish market are presented. Focus has been on SSL products for replacement of incandescent lamps and halogen spotlights. The warm white light and good color rendering properties of these traditional light sources are a must for lighting in Denmark and the Nordic countries. 266 SSL replacement lamps have been tested for efficiency and light quality with respect to correlated color temperature and color rendering properties. This shows a trade-off between high color rendering warm white light and energy efficiency. The lumen and color maintenance over time has been investigated and results for products running over 11000 h will be presented. A new internet based SSL product selection tool will be shown. Here the products can be compared on efficiency, light quality parameters, thus providing a better basis for the selection of SSL products for consumers.

High-end illumination devices based on LEDs require precise color matching, because the dominant wavelength depends on temperature and changes due to aging. We demonstrate the performance of multispectral sensors fabricated using a complementary metal-oxide semiconductor (CMOS) process for color-sensing feedback. Various plasmonic nanostructures were simulated and implemented to achieve band pass and cut-off filters, placed on top of photodiodes. These devices for multispectral sensing can be fabricated in high volume and measurements indicate that a wavelength change of 3 nm yields a relative signal change of more than 20 % due to the steep-edge characteristics of the filters.

Quantum dots (QDs) are rare-earth free downconverters which have been demonstrated as ideal phosphor replacement materials from an optical perspective, with the potential to enable a 30% or larger improvement in LED efficiency as compared to today’s rare-earth phosphors at the same quality of light (higher CRI implementations see larger improvements). However to date QDs have demonstrated less than ideal reliability under standard LED chip conditions, prohibiting cost-effective integration into conventional luminaire formats. This talk will discuss the present status and future prospects of QDs as LED downconverters, including recent advances in connecting quantum dot structure to high temperature and high intensity performance, an updated look at QD reliability, and the limits of QDs in a variety of phosphor configurations.

Color tunable wide gamut light covering the greenish, yellow-green, yellow, orange, and reddish tone chromaticity region in europium/erbium co-doped lead-cadmium-germanate PbGeO₃:PbF₂:CdF₂ glass phosphor is presented. The phosphors were synthesized, and their light emission properties examined under UV/blue light-emitting-diode excitation. Luminescence emission around 525, 550, 590, 610, and 660 nm was obtained and analyzed as a function of Eu/Er concentration, excitation wavelength, and glass host composition. The color tunability was actually obtained via proper combination of Er³⁺ and Eu³⁺ active ions concentration. The combination of the emission tone with a blue LED in the region of 400-460 nm, yields a mixture of light with color in the white-light region presenting a CCT in the range of 2000 to 4000 K. Results indicate that the color-tunable fluorolead germanate erbium/europium co-doped glass phosphor herein reported is a promising novel contender for application in LED-based solid-state illumination technology

With this work we report on the performance and degradation mechanism of commercially available remote phosphors (RP) for SSL. Thermal analysis indicates that phosphors can reach temperatures above 60°C during operation at an ambient temperature of 25°C when subjected to an optical power of 346 mW/cm2. We also demonstrate that temperature is a strong driving force for the degradation. Results indicate a gradual reduction in luminous flux output and a decrease of correlated color temperature as a consequence of stress. We demonstrate that the degradation rate is strongly correlated with stress temperature with an activation energy of 1.36 eV for a TTF of 70%.

ZnO and Ag-doped ZnO nanorods are fabricated by hydrothermal method. Effects of Ag doping on the ZnO nanorods have been investigated by various measurements. Introduction of Ag in ZnO nanorods has no effects on the surface morphology and growth habits of ZnO. Compared to ZnO nanorods, absorption wavelength shifts red after Ag doping, corresponding to decrease of optical band gap. It is suggested that defects band is introduced into Ag-doped ZnO. Luminescence of Ag-doped ZnO nanorods have been found to have two emission peaks centering at around 520 nm and 680 nm, which can be explained by oxygen vacancy and introduced defects, respectively. ZnO and Ag-doped ZnO nanorods inorganic/organic heterostructure LEDs are reported. The junction consists of nanorods and polymer, which is evaporated or spin-coated on the samples. Ag doping ZnO nanorods inorganic/organic heterostructure LED shows smaller leakage current and better rectification characteristic than pure ZnO nanorods LED device.

Human susceptibility to visual discomfort of solid-state lighting was investigated by statistically analyzing for commercial phosphor-converted white light-emitting diodes (PC-WLEDs) with considering optical characteristics such as correlated color temperature (C.C.T., or Tcp), chromaticity, lumen, color rendering Index (C.R.I.) , radiation pattern. These statistic analyses of human factor engineering were based on the surveys and visual measurements among 500 male and female volunteers of ages 18 to 22. The levels of these optical parameters were standardized for indication of the discomfort degree or sensitivity to human visual susceptibility. The results showed that, compared to male human eyes’, female ones could have 20% more sensitive to color rendering on R985 Index, 15% higher in color temperature; however, 30% less sensitive to lumen, and 30% lower recognition ability to radiation pattern. Consequently, it becomes more important for LED manufacturers and solid-state lighting designers to take consideration of such human factor engineering into their products and services.

It was reported that sol-gel processed SiO2-coating effects of Ce³⁺: YAG phosphor on and thermal reliability enhancements in terms of quantum efficiency and optical characteristics. This study found improved light extraction efficiencies of glass phosphor, and increased quantum efficiency 3.95% of SGCeYDG in comparison to un-coated CeYDLTG. In the thermal reliability tests, Lumen degradation and chromaticity shift (ΔE) in the SGCeYDG thermally agd at 150, 250, 350, and 450°C, respectively, are also presented and compared with those of CeYDG. The results clearly demonstrated that the SGCeYDG exhibited better thermal stability on lumen degradation, and chromaticity shift than CeYDG’s. The navel high performance thermal-stable glass has been essentially critical to the application areas of LED modules where high-power leading high-operation-temperature and absolute thermal reliability are required for developing the nextgeneration solid-state lighting industry.

Optical imaging systems are widely used in different applications including tracking for portable scanners; input pointing devices for laptop computers, cell phones, and cameras; and fingerprint-identification scanners. Also in optical navigation (military target tracking where tracking sensors follow airplanes, missiles, and other targets [1-4]. Since the two main parameters affecting the performance of the optical imaging systems are the optical source and the surface nature. So; The aim of the paper is to study how the optical source affects the performance of the optical imaging systems by exchange the operating surface of the optical imaging system with a standard diffuse object (Gabbor holograms) to study and analyze laser speckle pattern and Circular interference fringes produced by illuminating these standard diffusers using different optical sources [coherent (3mW diode laser, and 10mW He-Ne laser) or partially coherent light (LEDs)]. The Circular interference fringes were used to display the relations between the fringes order and its radii. From these relations we found that the electronic sensor can deliver the same accuracy of laser diodes when replacing it by commercial LEDs. So, we can design a new cheaper, high performance optical imaging system using commercial LED sources.

In this study, a process for optimizing the color temperature and lighting distribution on indoor LED lighting for human factor and energy saving is proposed. Based on the features of LED lighting, the diversified fixture design is more possibilities, such as the fixture with color-temperature and lighting distribution tunable. Therefore, the generalized reduced gradient optimization method is used to calculate the corrected color temperature of the fixture for the seat near the window affected by sun light. This research result could be used in the LED lighting design for more energy saving.

The concept of the remote phosphor is proven to be one of the effective solutions for improving luminous efficacy of pc-WLEDs by solving the problem of phosphor thermal and scattering loss. However, most of them need to use larger packaging design to enhance their performance. Such development is adverse to market trends, which also resulted in higher manufacturing costs and the difficulties in luminaire design. In this paper, we present the analysis of pc-WLEDs as the function of the packaging size and figure out its limitation, so that we can apply to reduce the device size but keep the luminous efficacy as high as possible.

The basic properties of indium-zinc oxide (IZO) were investigated from the view point of the potential of light-emitting diodes (LEDs) for nanostructured transparent contact. The resistivity and contact resistance to p-GaN were obtained to be 2.5×10^-4 Ωcm and 9.4×10^-4 Ωcm², respectively, which are comparable to those of indium-tin oxide (ITO). The light output of the LED with the moth-eye IZO was 10 % and 40 % higher than that of the LED with the moth-eye ITO and that of the LED without the moth-eye structure, respectively.

High performance 365 nm vertical-type ultraviolet light-emitting diodes (UV-LEDs) were developed using an embedded self-textured oxide (STO) structure using metal-organic chemical vapor deposition system. From etch-pit-density results, the dislocation densities of LED epilayers were effectively reduced to 5.6×106 cm-2 by inserting the STO structures due to the relaxation of residual stress. The vertical-type UV-LEDs are fabricated using a combination technique of metal bonding and sapphire substrate separation. When the UV-LEDs (size: 45 × 45 mil2) were driven with a 20 mA injection current, the output powers of the LEDs with and without STO were measured to be 10.2 and 5.51 mW, respectively. The external quantum efficiency of LEDs with STO exhibits 32% higher than that of LED without STO. As increasing injection current to 350 mA, a near 45 mW light output was measured from STO-LED sample. This benefit was attributed to the introduction of STO structure which can not only block the propagation of threading dislocations but also intensify the light extraction of LED.

We fabricated the colloidal quantum-dot light-emitting diodes (QDLEDs) with the HfO2/SiO2-distributed Bragg reflector (DBR) structure using a pulsed spray coating method. Moreover, pixelated RGB arrays, 2-in. wafer-scale white light emission, and an integrated small footprint white light device were demonstrated. The experimental results showed that the intensity of red, blue, and green (RGB) emissions exhibited considerable enhancement because of the high reflectivity in the UV region by the DBR structure, which subsequently increased the use in the UV optical pumping of RGB QDs. In this experiment, a pulsed spray coating method was crucial in providing uniform RGB layers, and the polydimethylsiloxane (PDMS) film was used as the interface layer between each RGB color to avoid crosscontamination and self-assembly of QDs. Furthermore, the chromaticity coordinates of QDLEDs with the DBR structure remained constant under various pumping powers in the large area sample, whereas a larger shift toward high color temperatures was observed in the integrated device. The resulting color gamut of the proposed QDLEDs covered an area 1.2 times larger than that of the NTSC standard, which is favorable for the next generation of high-quality display technology.

In this paper, we demonstrated a detective system to evaluate the quality and classification of different tea samples based on multi-wavelength LED-induced fluorescence spectroscopy. By utilizing multiple excitation wavelengths, we obtained much more physical and chemical information from the detected samples than single excitation wavelength. By utilizing principal component analysis (PCA), we extracted the dominant features of the samples to classify and characterize the tea samples.