Efficient White LEDs Research Articles

Highly emissive 0D Tin(II) hybrid for white LED

Highly emissive 0D Tin(II) hybrid for white LED

СТАН І ПЕРСПЕКТИВИ РОЗВИТКУ БІЛИХ СВІТЛОДІОДІВ З ВИПРОМІНЮВАННЯМ, НАБЛИЖЕНИМ ДО ПРИРОДНОГО

Innovative technologies for the production of modern LEDs have allowed leading manufacturers (Seoul Semiconductor, Samsung, Cree) to develop their own ways of producing highly efficient white LEDs characterised by radiation parameters close to natural light. Modern LED light source development technologies have led to a sharp decrease in the use of white light guides with a colour rendering index in the range of 70-75, while the new most efficient LEDs have a colour rendering index of at least 80, and LEDs with a colour rendering index of more than 90 are becoming more widely used. LEDs with a correlated colour temperature in the range of 3000-4500 K, which were not as commonly used before due to their lower efficiency, have become more widespread. To create energy-efficient lighting, it is now considered important to create LED lighting devices with a spectral composition of radiation close to white natural light, as it is the most acceptable for improving the psycho-physiological state of a person and adequate perception of the environment. The most comfortable and safe for humans is the value of the correlated colour temperature of light close to 4000-4500 K and the colour rendering index of more than 90 units. Leading lighting companies are successfully working on solving this problem. This paper analyses ways to improve the luminous efficiency and colour rendering index of white LEDs used by leading manufacturers of modern LEDs. The most efficient white LEDs with a colour rendering index in the range of 93-96 and a luminous efficiency of 105-200 lm/W are considered. In the face of fierce competition, leading manufacturers are addressing the issue of improving the quality of LED lighting equipment in their own ways, which ensures the continuous development of LED technologies. The maximum theoretically determined spectral efficiencies of white LEDs are about 370 lm/W, which may indicate possible significant achievements and significant prospects for the further development of LED lighting technology.

Optimizing the spectral composition of light from LED phytolighting systems to improve energy efficiency

The use of LEDs for plant lighting (phytolighting) provides a more energy- efficient alternative to traditional lighting methods. Combination of LEDs with different spectral composition and the possibility to change the composition of resulting radiation in a single lighting device allows one to improve the efficiency of phytolighting systems and optimize them for different conditions of plant growth and development. In this work, we have investigated quasi-monochromatic LEDs specialized for efficient phytolighting and efficient white LEDs with different CRI. Being based on the research, the most effective LEDs for building phytolighting systems have been identified, and their optimal ratio with red quasi-monochromatic LEDs for building phytolighting systems in rooms with a constant presence of people (greenhouses, winter gardens, etc) has been determined.

Photoluminescence properties of Sb3+-activated Ca2YTaO6 dual color emitting phosphors for plant growth LEDs applications

Photoluminescence properties of Sb3+-activated Ca2YTaO6 dual color emitting phosphors for plant growth LEDs applications

Antimony(III) based hybrid materials toward stable and highly efficient white LED

Antimony(III) based hybrid materials toward stable and highly efficient white LED

Enhancing light emission near low-refractive-index contrast nanostructures via mirror-symmetry breaking

A platform of recent interest and large application potential is one in which the light emitters are directly integrated with an optical metasurface. Plasmonic metals and high-refractive-index, dielectric Mie metasurfaces have been explored in this connection but have their challenges. We propose low-refractive-index, contrast nanostructured thin films for studying metasurface-emitter systems, specifically focusing on two configurations of practical importance: LED white light generation using color converting polymers and fluorescence-based sensing in aqueous media. To achieve light emission enhancement in a low-index contrast, low optical absorption setting, we exploit the excitation of quasi-bound states in the continuum modes in a mirror-symmetry broken grating. Our numerical study predicts widely tuneable sharp-linewidth emission enhancements, near-zero quenching, and large and controllable active volume in the grating vicinity, which are significant improvements in comparison with both plasmonic and high-index contrast, all-dielectric platforms. When compared with simple gratings, mirror-symmetry broken gratings give four times larger radiative enhancement. Our results are of interest in furthering experimental activity and realizing applications such as light converter for efficient white LEDs and smart detection electronics-integrated substrates for sensing.

Deep learning enabled inverse design of nanocrystal-based optical diffusers for efficient white LED lighting.

Angular color uniformity and luminous flux are the most important figures of merit for a white-light-emitting diode (WLED), and simultaneous improvement of both figures of merit is desired. The cellulose-nanocrystal (CNC)-based optical diffuser has been applied on the WLED module to enhance angular color uniformity, but it inevitably causes the reduction of luminous flux. Here we demonstrate a deep-learning-based inverse design approach to design CNC-coated WLED modules. The developed forward neural network successfully predicts two figures of merit with high accuracy, and the inverse predicting model can rapidly design the structural parameters of CNC film. Further explorations taking advantage of both forward and inverse neutral networks can effectively construct the coating layer for WLED modules to reach the best performance.

54.1: Invited Paper: Highly efficient Quantum Rods LEDs for LCD backlights

Efficient white LEDs with efficacy of > 200 lm/W are much desirable for lighting and displays. LCDs is the market leader with an approximate 70% market share, particularly in the medium‐ to large‐size display segment. The largest portion of power consumption for LCDs belongs to LCD backlight, accounting for 70%–80% of the total power consumption, which strongly depends on the content and resolution of display panels. [1–8] The polarizer and color filters are the two main components responsible for high‐power consumption. Although the phosphor‐based LED backlights are much more efficient than the CCFL backlight, the efficiency of display backlight LEDs varies in the range of 70–85 lm/W. A large portion of the phosphor‐based LED light is lost in color filters [1–5]. The LED efficacy further decreases at the high brightness required for outdoor applications [4]. Intensive efforts have been made to replace the phosphor with quantum dots‐based downconverters, but the efficiency and stability of these devices are still in their infancy. Quantum rods (QRs), the elongated shape nanoparticles, show superior properties such as relatively larger Stokes shifts, polarized emission, and high light out‐coupling efficiency in the solid‐state. The challenges are as follows: 1. high quantum yield of QRs in the thin solid films covering the whole visible range; 2. good in‐plane alignment of the QRs on the LEDs; and 3. high photo‐stability and low‐temperature quenching. In this talk, we will try to discuss all these challenges. We will also discuss the merits of gradient alloyed CdSe/ZnXCd1‐XS/ZnS and CdSe/CdS/ZnS core/shell/shell QRs downconverters showing high efficacy LEDs covering a wide color gamut. These QRs‐based LEDs attain the luminous efficacy (LE) of 149 lm/W (@10mA), wide color gamut (118% NTSC), which is exceedingly higher than the state‐of‐the‐art quantum dot and phosphor‐based on‐chip LED, which paves the way for the future display backlight with the efficacy of > 200 lm/W.

Novel niobates Y3NbO7: Ln3+ (Ln=Pr, Sm) phosphors for warm white LED: Synthesis and luminescent properties

Nowadays, the combination of red, blue and green light is one of the mainstream ways to realize high efficient white LED. In this work, novel niobates Y 3 NbO 7 : Ln 3+ (Ln = Pr, Sm) phosphors have been successfully synthesized by the conventional high temperature solid-state method. The phase composition, luminescent properties and luminescence decay were investigated in detail. Y 3 NbO 7 : Ln 3+ (Ln = Pr, Sm) phosphors manifested a bright red or yellowish-red emission band. The optimum doping concentration and critical energy transfer distance of Y 3 NbO 7 : Ln 3+ (Ln = Pr, Sm) were determined. The concentration quenching mechanism of Y 3 NbO 7 : Ln 3+ (Ln = Pr, Sm) attributed to the electric dipole-dipole interaction. The Y 3 NbO 7 : Ln 3+ (Ln = Pr, Sm) phosphors exhibited abnormal thermal quenching phenomenon and the luminescence intensity at 453K remained about 78% and 88% of its values at room temperature for Y 3 NbO 7 : Pr 3+ and Y 3 NbO 7 : Sm 3+ respectively. All results indicated that Y 3 NbO 7 : Ln 3+ (Ln = Pr, Sm) as a red or yellowish-red phosphor-converted component could be potentially applied in warm white LED. • Novel niobates Y 3 NbO 7 : Ln 3+ (Ln = Pr, Sm) phosphors were prepared by high-temperature solid-state reaction. • Detailed optical properties of Y 3 NbO 7 : Ln 3+ (Ln = Pr, Sm) were investigated. • Y 3 NbO 7 : Ln 3+ (Ln = Pr, Sm) phosphors exhibited excellent thermal stability; and the luminescence intensities at 453K remained above 75% of their values at room temperature. • Temperature-dependent photoluminescence spectra, concentration quenching mechanism, chromaticity coordinates and decay times of the samples were studied.

Room‐Temperature Treatment with Thioacetamide Yielding Blue‐ and Green‐Emitting CsPbX3 Perovskite Nanocrystals with Enhanced Photoluminescence Efficiency and Stability

AbstractWhile multiple protocols are currently available for obtaining green‐ and red‐emitting lead halide perovskite nanocrystals (NCs) with near‐unity photoluminescence quantum yield (PLQY), achieving this target for the blue‐emitting NCs is still quite challenging. This is an impediment to the development of perovskite‐based highly efficient white LEDs of which blue is an essential component. Herein, we show that room‐temperature treatment of the blue‐emitting CsPbCl1.5Br1.5, cyan‐emitting CsPbClBr2 and green‐emitting CsPbBr3 NCs with thioacetamide not only enhances the PLQY to near‐unity (∼97–99%) without affecting the PL maximum and bandwidth, but also improves the stability of the systems significantly. The investigation reveals that effective passivation of under‐coordinated surface Pb2+ through formation of Pb−S and Pb−NH2 bonds and removal of excess lead atoms suppress the nonradiative recombination channels and enhances the PLQY and stability of the NCs. Outstanding PL efficiency and superior long‐term stability make these systems potential ingredients for various lighting and display applications.

Acridine based metal-organic framework host-guest featuring efficient photoelectrochemical-type photodetector and white LED.

A novel metal-organic framework (MOF) host-guest material [Cd3(EtOIPA)4(HAD)2]·H2O has been successfully synthesized by the reaction of 5-ethoxyisophthalic acid (EtOIPA), acridine (AD) and Cd(II) salts under hydrothermal conditions. Structurally, the title MOF possesses a trinucleate Cd(II) based 2D double-layer with the protonated AD cations as the template encapsulated into the grids. The combination of experiments and theoretical calculations reveals that the orderly arrangement of EtOIPA dimers, protonated AD cations and trinucleate Cd(II) clusters generates highly delocalized π-electron channels with a prolonged exciton lifetime. The MOF powders show bright yellow emission with a long lifetime of 50.63 ns. Photoelectrochemical measurements reveal a high photocurrent density ratio of 290 between light and dark conditions at 0 V bias potential, making it a perfect self-driven photodetector. By coating the yellow phosphor on a commercially available blue LED, a high performance white LED with CIE, CCT and CRI values of (0.325, 0.336), 88.2 and 5844 K, respectively can be obtained.

Synthesis of Highly Luminescent InP/ZnS Quantum Dots with Suppressed Thermal Quenching

InP quantum dots (QDs) are promising down-conversion phosphors for white light LEDs. However, the mainstream InP QDs synthesis uses expensive phosphorus source. Here, economic, in situ-generated PH3 is used to synthesize InP QDs and a two-step coating of ZnS shells is developed to prepare highly luminescent InP/ZnS/ZnS QDs. The QDs show a photoluminescence quantum yield as high as 78.5%. The emission can be tuned by adjusting the halide precursor and yellow emissive InP/ZnS/ZnS QDs are prepared by judiciously controlling the synthetic conditions. The yellow QDs show suppressed thermal quenching and retain >90% room temperature PL intensity at 150 °C for the growth solution. Additionally, the PL spectrum matches with the eye sensitivity function, resulting in efficient InP QD white light LEDs.

Large-Area Nanocrystalline Caesium Lead Chloride Thin Films: A Focus on the Exciton Recombination Dynamics.

Caesium lead halide perovskites were recently demonstrated to be a relevant class of semiconductors for photonics and optoelectronics. Unlike CsPbBr3 and CsPbI3, the realization of high-quality thin films of CsPbCl3, particularly interesting for highly efficient white LEDs when coupled to converting phosphors, is still a very demanding task. In this work we report the first successful deposition of nanocrystalline CsPbCl3 thin films (70–150 nm) by radio frequency magnetron sputtering on large-area substrates. We present a detailed investigation of the optical properties by high resolution photoluminescence (PL) spectroscopy, resolved in time and space in the range 10–300 K, providing quantitative information concerning carriers and excitons recombination dynamics. The PL is characterized by a limited inhomogeneous broadening (~15 meV at 10 K) and its origin is discussed from detailed analysis with investigations at the micro-scale. The samples, obtained without any post-growth treatment, show a homogeneous PL emission in spectrum and intensity on large sample areas (several cm2). Temperature dependent and time-resolved PL spectra elucidate the role of carrier trapping in determining the PL quenching up to room temperature. Our results open the route for the realization of large-area inorganic halide perovskite films for photonic and optoelectronic devices.

51.4: Design of highly efficient white LED for the maximal CRI

Phosphor‐converted white light emitting diodes (pc‐LEDs) are being used as a source of artificial lighting. One of the main goals of artificial lighting is to make objects/images look natural — as they look under the sunlight. The ability of a light source to accurately render the natural color of an object is gauged by the color rendering index (CRI) and a conventional pc‐LED has an average CRI—CRI Ra ~ 80 which is not suitable for artificial lighting. In order to fabricate the pc‐LEDs for artificial lighting applications, all the CRI points (R1 — R15) should be above 95. Herein a novel design strategy of an LED package (PKG) is implemented to achieve CRI points ≥ 95 through introducing two blue LEDs and a UV LED in combination with green and red phosphors. The silicone encapsulant, the ratio of the current through the LEDs, and the phosphor ratio were optimized for achieving high efficiency (~ 100 lm/W) as well as all the CRI points above 95. Our re‐designed LED PKG with an efficiency of around 100 lm/W would find applications in stadium lighting as well as for ultra‐high definition television production where high CRI points are required for the light source.

Perovskite Nanocrystal Fluorescence-Linked Immunosorbent Assay Methodology for Sensitive Point-of-Care Biological Test

Summary Quantitative fluorescence immunoassay is a vital and convenient method in point-of-care (POC) testing for food safety and clinical healthcare. However, current marking materials, from organic luciferin to quantum dots, still lack the requirement of increasing need for multiple targets of interest because of their too broad emission. Here, a new label material, perovskite nanocrystals (Pe-NCs), with a narrower photoluminescence spectrum is reported, and a sensitive and quantitative immunoassay method named the perovskite nanocrystal fluorescence-linked immunosorbent assay is preliminarily demonstrated. The key point of realizing water-dispersed and stable Pe-NCs was addressed by functionalizing with hydroxyl groups. The fluorescent probes (perovskite antibody) were constructed via electrostatic adsorption with narrow full-width at half-maximum (∼18 nm), laying the foundation for future study of multi-target detection. Both indirect competitive immunity and sandwich immunoassay were successfully demonstrated. This work provides a possible label material for POC tests and may open up a promising avenue of next-generation immunoassay.

Erratum to: Highly efficient and stable white LEDs based on pure red narrow bandwidth emission triangular carbon quantum dots for wide-color gamut backlight displays

Erratum to: Highly efficient and stable white LEDs based on pure red narrow bandwidth emission triangular carbon quantum dots for wide-color gamut backlight displays

Versatile Homoleptic Naphthyl‐Acetylide Heteronuclear [Pt2M4(CC‐Np)8] (M = Ag, Cu) Phosphors for Highly Efficient White and NIR Hybrid Light‐Emitting Diodes

AbstractA new family of low‐energy emitting organic phosphors (OPs) based on [Pt2M4(CC‐1‐Np)8] clusters, in which M is either Ag(I) (1) or Cu(I) (2) and CC‐1‐Np is the strongly delocalized 1‐naphthylacetylide ligand, are presented. The inclusion of the 1‐naphthylacetylide moiety is crucial to achieve very emissive and stable OPs that do not experience photoinduced heat generation and oxidation in both white and NIR hybrid light‐emitting diodes (HLEDs) operating under ambient conditions. In short, the first use of these novel OPs leads to i) HLEDs with NIR emission centered at 730 nm, color purity close to 0.99, and remarkable luminous efficacies of ≈1.5 lm W−1 that is comparable to commercial NIR‐LEDs and ii) daylight white LEDs with luminous efficacies of 75 lm W−1 and stabilities of >500 h. Thus, this work provides relevant information for the synthesis, design, and application of a new family of low‐energy emitting OPs toward efficient and stable white and NIR hybrid LEDs.

Novel red-emitting CsPb1−xTixI3 perovskite QDs@glasses with ambient stability for high efficiency white LEDs and plant growth LEDs

Abstract Currently, the application of all-inorganic cesium lead halide perovskite (CsPbX 3 , X = Cl, Br, I) quantum dots (QDs) is limited due to toxicity of lead and poor ambient stability. In our work, a series of Ti-doped CsPbI 3 QDs were successfully prepared in borosilicate glass (SiO 2 -B 2 O 3 -ZnO) by the melt quenching and in situ crystallization technique. The samples showed excellent water/thermal stability, and the tunable emission (650–695 nm) was controlled by different Ti contents and heat treatment temperatures. In particular, the optical properties of CsPb 1− x Ti x I 3 QDs@glasses (x ≤ 0.5) are superior to those of pristine CsPbI 3 QDs@glass. As a result, the wLED was assembled using red-emitting CsPb 1− x Ti x I 3 QDs@glasses and yellow-emitting Ce 3+ :YAG phosphor under excitation of InGaN blue chip, which demonstrated an outstanding luminous efficiency of 102.44 lm/W, a high color rendering index of 80.6. Particularly, Ti-doped CsPbI 3 QDs@glasses with red and far-red light are combined with a blue-chip to assemble an LED device, which exactly satisfies the lighting conditions of plant growth.

Highly efficient and stable white LEDs based on pure red narrow bandwidth emission triangular carbon quantum dots for wide-color gamut backlight displays

High-performance white light-emitting diodes (WLEDs) hold great potential for the next-generation backlight display applications. However, achieving highly efficient and stable WLEDs with wide-color-gamut has remained a formidable goal. Reported here is the first example of pure red narrow bandwidth emission triangular CQDs (PR-NBE-T-CQDs) with photoluminescence peaking at 610 nm. The PR-NBE-T-CQDs synthesized from resorcinol show high quantum yield (QY) of 72% with small full width at half maximum of 33 nm. By simply controlling the reaction time, pure green (PG-) NBE-T-CQDs with high QY of 75% were also obtained. Highly efficient and stable WLEDs with wide-color-gamut based on PR- and PG-NBE-T-CQDs was achieved. This WLED showed a remarkable wide-color gamut of 110% NTSC and high power efficiency of 86.5 lumens per Watt. Furthermore, such WLEDs demonstrate outstanding stability. This work will set the stage for developing highly efficient, low cost and environment-friendly WLEDs based on CQDs for the next-generation wide-color gamut backlight displays.

Luminescence properties of Li2SrSiO4:Eu2+ silicate yellow phosphors with high thermal stability for high-power efficiency white LED application

Abstract Li2SrSiO4:Eu2+ yellow phosphors were synthesized by Polymerized Complex Method using TEOS and their thermal stability was investigated. The synthesized phosphors exhibited a broad yellow emission band around 560 nm. The optimum H2/N2 reduction temperature and Eu concentration are 900 °C and 0.5% respectively, which show the highest PL intensity and 6 times higher than samples synthesized by conventional solid-state reaction at the same condition. In order to investigate the thermal stability, PL properties in temperature range from 16.4 K to 583 K were examined. The PL intensity remains 80% above at high temperature (438 K) compared with room temperature. Activation energy and internal quantum efficiency of samples are estimated to be 0.43 eV and 62% respectively. Emission processes in Li2SrSiO4:Eu2+ phosphor were discussed with configuration coordinate model. The results reveal that Li2SrSiO4:Eu2+ yellow phosphors shows excellent thermal stability and have feasibility in replacement of YAG:Ce3+ yellow phosphors in white LEDs application.