High‐efficiency UV LEDs and RGB white LEDs for lighting and LCD backlights

Abstract— Progress in the development of blue light‐emitting diodes and yellow phosphor has led to the realization of solid‐state lighting. The development was followed by improvement in the luminous efficacy of ultraviolet light‐emitting diodes (UV‐LEDs). By using near‐UV‐LEDs (n‐UV‐LEDs) excited light for red, green, and blue (RGB) phosphors, a new type of solid‐state lighting was realized. An innovative method for increasing the efficiency of LEDs by using a silicon nitride layer as the active layer and piling them up to a nano‐sized level with nano‐sized holes has been developed.     

Flexible organic light‐emitting‐diode‐based photonic skin for attachable phototherapeutics

Phototherapeutics is both safely noninvasive and can be employed to treat a variety of sites and diseases. Current rigid and bulky conventional light sources, such as LED or laser‐based phototherapy devices, are difficult to transport and use for regular irradiation treatments. To solve this problem, flexible organic light‐emitting diode (OLED) light sources are the best candidates, and if applied very thinly as a skin‐like platform, the ultimate attachable phototherapeutics can be realized. We demonstrated a very thin flexible OLED‐based photonic skin with a total thickness of 6 μm for application in attachable phototherapeutics. It was optimized by controlling the peak wavelengths (600–700 nm) and irradiation interval of the flexible OLED thus improving the regeneration effect of the artificial skin by up to 70%. In addition, when the flexible OLED‐based photonic skin was attached to a dressing film before being applied to the skin, it delivered the same electro‐optical properties, while protecting against external contamination. The OLED skin on the dressing film had an operating lifetime of more than 100 h. These results confirmed the applicability of flexible OLED‐based photonic skin to various light treatment areas, such as surgical wounds that require periodic irradiation.     

Influence of wavelength red‐shift on color‐rendering index and luminous efficacy of LEDs

Abstract— The peak wavelength of light‐emitting‐diodes(LEDs) shifts towards the longer wavelengths when the temperature of the LED chip increases. The color‐rendering index (CRI) and luminous efficacy may change with the peak wavelength of the LED, and it is not expected to do so when the LEDs are used in fields which require a high CRI and luminous efficacy. A mathematical model of the LED spectrum was used to analyze the influence of the wavelength shift on the CRI and luminous efficacy of three‐ and four‐chip‐packaged LEDs, respectively. The results show that the CRI decreases with the peak wavelengths shifting towards longer wavelength for both three‐ and four‐chip LEDs; especially, the CRI of the four‐chip LEDs decreases more for a green‐color wavelength shift than for other colors. The luminous efficacy increases with a green‐color wavelength shift and decreases with a red‐color wavelength shift.     

High efficiency heavy metal free QD‐LEDs for next generation displays

In this paper, we report on our progress on developing heavy metal free (or Cd‐free) QD‐LEDs for all three colors. With improvement in synthesis, we have developed high quantum yield heavy metal free quantum dots (more than 95% for red and green and more than 80% for blue), with peak wavelengths suitable for BT.2020. Building upon these high‐performance quantum dots and through novel device structure design and optimization we have demonstrated high efficiency heavy metal free QD‐LEDs with EQE = 16.9%, 13%, 9% for red, green, and blue, respectively. Specifically, we report a systematic study on the impact of shell thickness to the device efficiency performance.     

Power‐saving primary design for displays enclosing a target color gamut

Abstract— Display primaries are optimized for the trade‐off between the total primary power and color gamut under the requirement that a target color gamut is enclosed by the color gamut of the display. LED displays and HDTV color gamut are taken as examples. Compared to the display using a set of typical commercial RGB LEDs, it was found that a total optical (electrical) power of 23.6% (15.6%) can be saved for the display using optimal RGB LEDs. Although the size of the display color gamut is sacrificed, the color gamut of the display using optimal RGB LEDs still encloses the HDTV color gamut. The combined effect of the LED luminous efficiency and white‐point condition on the determination of the optimal LED wavelengths and bandwidths is also studied.     

Phototherapy

Phototherapy has been used for the treatment of psoriasis for decades and has been proved effective. Beyond psoriasis, the spectrum of skin diseases found to respond to phototherapy has broadened considerably in recent years. It is used in atopic eczema, eosinophilic pustular folliculitis, urticaria and photodermatoses. Recently there have been changes in the treatment. Other wavebands are being used in phototherapy such as 311 nm, and maintenance therapy is usually applied. Finally, phototherapy is also used for other disorders unrelated to dermatology such as neonatal hyperbilirubinemia.     

Simulated light extraction from a light‐emitting diode integrated with a microlens array

Abstract— Light extraction from InGaN‐based light‐emitting diodes (LEDs) on which microlens arrays were integrated using ray‐tracing methods was simulated. Enhancement of the total light extraction and beam shaping in the forward direction of the output of microlens‐integrated LEDs compared to conventional LEDs were observed. The diameter, curvature radius, and density of the microlens arrays on the LEDs were varied and the optimal conditions for external efficiency was determined.     

不同波长近红外光下手掌静脉图像质量分析

在手掌静脉成像系统中,为对光源波长和成像质量之间的关系进行研究,对手掌皮肤中的表皮层、真皮层和脂肪层在近红外光下的吸收、散射光学特性建立数学模型,并对在760 nm、850 nm、890 nm和960 nm四种单波长近红外光下图像质量的影响因素进行分析。在上述四种单波长及其六种混合波长下,利用图像对比度作为图像质量评价标准,对2 500张掌脉图像进行了预处理和图像质量对比分析。实验结果和理论分析表明,在混合波长760 nm+960 nm下,最大程度保留了静脉信息。     

Non‐polar‐oriented InGaN light‐emitting diodes for liquid‐crystal‐display backlighting

Abstract— This article addresses spontaneously polarized light emission from GaN‐based light‐emitting diodes (LEDs) fabricated on electrically non‐polar crystallographic orientations and application of spontaneously polarized emission for backlighting of liquid‐crystal displays (LCDs). The first half of the article describes polarized light emission from GaN‐based LEDs and its role in solid‐state lighting technology. The second half reports on our experimental work to explore the potential of non‐polar LEDs for LCD backlighting applications. Optical transmission of non‐polar LED emission was characterized through a liquid‐crystal layer. Extinction ratios of 0.21 were measured between zero and an applied bias voltage to the liquid‐crystal cells. These extinction ratios are not particularly high yet; nevertheless, the experiment has demonstrated the potential of such non‐polar LEDs for LCD backlighting.     

Low level light therapy by Red–Green–Blue LEDs improves healing in an excision model of Sprague–Dawley rats

There are many methods of healing wounds. Among these, light therapy is reported to be beneficial, as beams assist the human body in treating, sterilizing, and regenerating cells. Both Laser and LED irradiation with specific wavelengths induce proliferation of fibroblasts depending on the wound area or wavelength and are effective in wound healing. This study used 8-week-old 250–300 g Male Sprague–Dawley Rats (ILAR Code: NTacSam:SD). The experiment was carried out for the non-irradiation group and the Red–Green–Blue LEDs irradiation groups (n of each group = 5). The experiment animals were relieved for 24 h after wounds had been excised and then the Red–Green–Blue LEDs irradiation groups were given irradiation therapy over 9 days 1 h per day. Immunohistochemical staining was conducted for cytokeratin in order to precisely measure the defect size. Also, Masson’s trichrome staining was conducted for comparison of collagen between the Red–Green–Blue LEDs irradiation groups and the non-irradiation group. Animals treated with Blue LEDs irradiation (p < 0.05), Green LEDs irradiation (p < 0.05), and Red LEDs irradiation (N.S.) healed at a faster rate than non-irradiated group. The LEDs irradiated groups also had more collagen, according to Masson’s trichrome staining for collagen analysis. The Red–Green–Blue LEDs irradiation had a beneficial effect on wound healing and could probably replace low power laser treatment.     

Fabrication of UV range light guide plate

The light guide plate, as part of the backlight unit in a cellular phone or liquid crystal display, has evolved to meet market demands for low power consumption, high-luminance and high-quality displays. Along with the advance of the light guide plate, LEDs have undergone development as light source for light guide plates. Surpassing the limitations of LED emission in the visible light range, LEDs that emit UV light have been developed. In recent years, the UV light are used as a source of light of the air cleaner, and it is used as a source of light to activate the titanium oxide which is photocatalyst. But common UV light sources are either line or point light sources. We study surface illuminators that incorporate diffusers in the visible light range. Applying our existing technology, we constructed an unprecedented UV surface illuminator (surface light source) and measured it using a photocatalyst. The experiment results are presented in this report.     

Thermal management of edge‐lit wide color gamut backlight for LCD using red laser diodes and cyan LEDs

The color gamut is one of the critical parameters that dictate the image quality of displays. The liquid crystal displays using white color light‐emitting diodes (LEDs) as the backlight, though having been widely employed recently, are not very satisfactory in terms of their color gamut because of the broad spectrum inherent to white LEDs. This prompted the authors to develop improved liquid crystal displays using an edge‐lit wide color gamut backlight that used red laser diodes and cyan LEDs. Generating laser beams with high color purity, the laser diodes are light sources with a significant effect on expanding the color gamut. However, laser diodes, red ones in particular, have unfavorable thermal characteristics. To cope with this shortcoming, the authors clearly defined the restrictive criteria for laying out two kinds of light source on the edge‐lit backlight and made a prototype 55‐type laser backlight for performance evaluation.     

Color tuning of indium phosphide quantum dots for cadmium‐free quantum dot light‐emitting devices with high efficiency and color saturation

Semiconductor quantum dots (QDs) promise facile color tuning and high color saturation in quantum‐dot light‐emitting devices (QD‐LEDs) by controlling nanoparticle size and size distribution. Here, we demonstrate how this promise can be practically realized for the cadmium‐free InP/ZnSe/ZnS multishell quantum dots. We developed a set of synthesis conditions and core/shell compositions that result in QDs with green, yellow, and red emission color. The QD‐LEDs employing these QDs show efficient electroluminescence (EL) with luminance up to 1800 cd/m² and efficiency up to 5.1 cd/ A . The color coordinates calculated from the EL spectra clearly demonstrate the outstanding color saturation as an outcome of the narrow particle size distribution. These results prove that the performance gap between cadmium‐free and cadmium‐based QDs in QD‐LEDs is shrinking rapidly.     

Highly efficient large‐sized LED display with improved ergonomics

Abstract— We have proposed a new approach to engineering and manufacturing an indoor indicator based on energy‐effective super‐bright LEDs. In our design, the light from a small number of such LEDs was uniformly redistributed using a special light guide. Recently, we developed a multi‐segment (40) LED indicator with improved ergonomics and a luminance of up to 4000 cd/m². This indicator is also capable of displaying (apart from the digits) special symbols.     

Terra and Aqua MODIS inter‐comparison of three reflective solar bands using AVHRR onboard the NOAA‐KLM satellites

Cross‐sensor inter‐comparison is important to assess calibration quality and consistency and ensure continuity of observational datasets. This study conducts an inter‐comparison of Terra and Aqua MODIS (the MODerate Resolution Imaging Spectroradiometer) to examine the overall calibration consistency of the reflective solar bands. Observations obtained from AVHRR (the Advanced Very High Resolution Radiometer) onboard the NOAA‐KLM series of satellites are used as a transfer radiometer to examine three MODIS bands at 0.65 (visible), 0.85 (near‐IR) and 1.64 µm (far near‐IR) that match spectrally with AVHRR channels. Coincident events are sampled at a frequency of about once per month with each containing at least 3000 pixel‐by‐pixel matched data points. Multiple AVHRR sensors on‐board NOAA‐15 to 18 satellites are used to check the repeatability of the Terra/Aqua MODIS inter‐comparison results. The same approach applied in previous studies is used with defined criteria to generate coincident and co‐located near nadir MODIS and AVHRR pixel pairs matched in footprint. Terra and Aqua MODIS to AVHRR reflectance ratios are derived from matched pixel pairs with the same AVHRR used as a transfer radiometer. The ratio differences between Terra and Aqua MODIS/AVHRR give an indication of the calibration biases between the two MODIS instruments. Effects due to pixel footprint mismatch, band spectral differences and surface and atmospheric bi‐directional reflectance distributions (BRDFs) are discussed. Trending results from 2002 to 2006 show that Terra and Aqua MODIS reflectances agree with each other within 2% for the three reflective solar bands.     

Submicron full‐color LED pixels for microdisplays and micro‐LED main displays

We demonstrate a bottom‐up approach to the construction of micro‐LEDs as small as 150 nm in lateral dimension. Molecular beam epitaxy (MBE) is used to fabricate such nanostructured LEDs from InGaN, from the blue to red regions of the spectrum, providing a single material set useful for an entire RGB display.     

Hybrid aligned nematic liquid crystal smart glass with asymmetrical daylight controls

We have proposed a hybrid alignment nematic liquid crystal cell using a polymer‐stabilized technology. The cell shows a reverse mode scattering property and is transparent at any viewing angle in the off‐state. The cell turns to opaque in the on‐state and has an asymmetrical scattering property at incident angles. Applying the cell to a smart glass, the cell can selectively scatter a midday sunlight with a function of window blinds. In a polymerization process, an ultraviolet (UV) penetration depth is carefully considered, which results in a change of polymer morphology. The UV irradiation from a homogeneous alignment substrate side causes a polymer‐rich layer near the substrate and the stronger scattering in the on‐state.     

Investigation of distributed Bragg reflector growth conditions for high‐brightness AlGaInP light‐emitting diodes

Abstract— The effect of growth conditions of a distributed Bragg reflector (DBR) structure on the performance of AlGaInP light‐emitting diodes (LEDs) have been investigated. Increasing the growth temperature and the flow rate of AsH₃ as well as lowering the growth pressure resulted in improved reflectivity and root‐mean‐square (RMS) roughness of the high‐aluminum‐content multiple pairs of the DBR structure. An increase in the growth temperature may improve the mobility of atoms on the surface for the positioning of the right atomic site and to reduce oxygen incorporation. An increase in the flow rate of AsH₃ can suppress the arsenic vacancy formation at higher V/III ratios. Furthermore, reduction in growth pressure can suppress the convection flow on the epitaxial growth surface. To verify the influence of DBR growth conditions on the successive growth of LED structures, the growth of full LED structures having two different DBR growth conditions was performed, and AlGaInP red LEDs using full LED structures were fabricated. It was found that higher growth temperature and AsH₃ flow rate with lower growth pressure for the DBR structure produced improved output power of the AlGaInP LEDs, which can be attributed to the high reflectivity and low RMS roughness of the DBR structure.     

High‐resolution and high‐brightness full‐colour “Silicon Display” for augmented and mixed reality

High‐brightness micro‐LED display bonded onto silicon backplane has been successfully demonstrated. The 0.38‐inch full‐colour active matrix LED microdisplay system consists of 352 × 198 pixels. Each pixel is 24 μm square composed of red, green, and blue (RGB) subpixels corresponding to a pixel resolution of 1053 ppi. Quantum‐dot materials are formed on III‐nitride blue micro‐LED array to convert blue light into red and green for full‐colour operation. We have confirmed that this microdisplay, which we call “Silicon Display” has wide colour gamut exceeding 120% of sRGB. We describe the advantage of this colour‐converting approach for the full‐colour micro‐LEDs. Progress toward higher resolution is also described. Brightness of more than 30 000 cd/m² has been confirmed at a driving current density of 4 A/cm² for 3000 ppi blue monochrome micro‐LED prepared for full‐colour Silicon Display. We believe our “Silicon Display” is ideally suited for near‐to‐eye displays for augmented and mixed reality.