Luminous Efficacy Research Articles

Hole Transport Layer Microroughening for Waveguide Mode Extraction in Organic Light‐Emitting Diodes

Herein, simple and scalable approach to enhance the out‐coupling efficiency in organic light‐emitting diodes (OLEDs) is presented. By exposing the 4,4′‐bis[N‐(1‐naphthyl‐1‐)‐N‐phenylamino]‐biphenyl (NPB) hole transport layer to hydrofluoroether (HFE) solvent for several minutes, a controllable microroughening of the film is achieved, which results in the formation of random scattering centers in the OLED structure. Optimized NPB microroughening for phosphorescent OLED with Ir(ppy)3 emitter leads to luminous efficacy improvement of 23% (from 64 to 79 lm W−1 at 1000 cd m−2) without additional external out‐coupling. Angular resolved spectroscopy of the OLED with an internal scattering layer reveals constant color almost independent of the viewing angle and Lambertian intensity distribution.

Enhanced Luminous Efficacy and Stability of InP/ZnSeS/ZnS Quantum Dot-Embedded SBA-15 Mesoporous Particles for White Light-Emitting Diodes.

Environmentally friendly quantum dots (QDs) of InP-based materials are widely investigated, but their reliability remains inadequate to realize their full potential and wide application. In this study, InP/ZnSeS/ZnS QDs (pristine QDs) were dispersed and embedded into Santa Barbara Amorphous-15 mesoporous particles (SBA-15 MPs) for the first time. A solvent-free method for preparing QD white light-emitting diodes (WLEDs) that is compatible with the WLED packaging process was developed. The photoluminescence (PL) spectrum of pristine QD powder exhibited cluster states and had huge redshift of approximately 23 nm. By comparison, the PL spectrum of the SBA-15 MP/QD hybrid powder had a slight redshift of approximately 8 nm, only because the pristine QDs were dispersed and embedded well in the SBA-15 MPs. The PL intensity of the SBA-15 MP/QD hybrid powder slightly decreased after heating and cooling compared with that of the pristine QDs. Moreover, the luminous efficacy of the SBA-15 MP/QD hybrid WLEDs was enhanced by approximately 14% compared with that of the pristine QD-WLEDs. Furthermore, reliability analysis revealed that the SBA-15 MPs could improve the stability of the pristine QDs on chips. Thus, these MPs promise good potential for applications in mini-LEDs in the future.

Estimation by ANN of Luminous Efficacy of Lamps Used for Lighting

The increase in energy production costs, and the increasing demand for energy have made energy saving necessary. Energy saving in lighting is able to be actualized by providing economically the same level of light without decreasing the illumination quality. A good lighting is possible by directing required amount of light to spaces desired to be lit. For a good lighting, efficiency factor is a significant measure. By adjusting the luminous efficacy in lamps, the electric energy to be consumed by the lamps is able to be minimized. The electric energy consumed for producing luminous energy will be less at the extent of greatness of luminous efficacy. In this study, the luminous efficacy of lamps of different brands were estimated by the use of data regarding voltage rating, power rating, and total luminous rating of lamps. According to the results of the analysis made by the developed ANN model, the luminous efficacy of lamps of different brands were estimated with an accuracy rate of above 98%. Regarding the lighting systems to be developed, the selection of lamps will be made based on their ability to provide economically the same level of light without decreasing the lighting quality, and to provide the required luminous efficacy for increasing the luminous efficacy.

Highly Efficient Broad-Band Green-Emitting Cerium(III)-Activated Garnet Phosphor Allows the Fabrication of Blue-Chip-Based Warm-White LED Device with a Superior Color Rendering Index.

High-performance warm-white light-emitting diode (LED) devices are in great demand toward green and comfortable solid-state lighting. Herein, we report a creative green-emission CaY2HfGa(AlO4)3:Ce3+ phosphor. CaY2HfGa(AlO4)3:Ce3+ compounds with different cerium ion doping contents have been successfully prepared through a conventional high-temperature solid-state method, and their phase and crystal structure have been revealed via the powder X-ray diffraction and Rietveld refinement. Impressively, the CaY2HfGa(AlO4)3:Ce3+ phosphors exhibit a broad-band excitation, which well covers the wavelength region from the 300 to 500 nm, corresponding to the commercial blue-emitting LED chip. Upon 450 nm excitation, the optimal CaY2HfGa(AlO4)3:2%Ce3+ sample shows an intense broad-band green emission (the corresponding testing spectral range: 460-750 nm) with a strongest peak about 534 nm. In addition, the CaY2HfGa(AlO4)3:2%Ce3+ sample possesses a broad full width at half-maximum equal to 120 nm; moreover, its CIE chromaticity coordinate and the internal quantum efficiency are determined to be (0.3541, 0.5427) and 72.8%, respectively. A high-quality warm-white LED has been fabricated through incorporating our CaY2HfGa(AlO4)3:2%Ce3+ green phosphors and commercial red phosphors with the 450 nm blue LED chip. When upon the 20 mA bias driving current, the LED device demonstrates a bright warm-white light emission, which possesses a satisfactory color rendering index of 91, a low correlated color temperature of 4080 K, as well as a good luminous efficacy of 85.14 lm W-1. The creative green-emitting CaY2HfGa(AlO4)3:Ce3+ garnet phosphor has a bright application prospect toward high-quality warm-white LED lighting.

Technical–Economic Analysis of the Solutions for the Modernization of Lighting Systems

In the context of the electricity crisis, measures are needed to reduce energy consumption. The case study was conducted on the lighting system at a university sports hall. To determine the efficiency and quality, the lighting systems and technical characteristics of the sources used were identified, lighting level measurements were made, the luminotechnical coefficients and the power of the whole lighting system were calculated and the results were compared to the values set out in the standards. Following analysis, the lighting system was found not to meet the quality requirements and was energy inefficient. For financial efficiency, only the replacement of lighting was sought, keeping the same equipment and granting the same facilities to the building users. Some lighting source options were analyzed and the option to have the highest luminous efficacy and the highest energy class was chosen. The analysis shows that the investment is amortized within a maximum of 17 months. The innovative aspect is based on linking the measurements with the determination of power and the proposal of modernization solutions, which shows the need for investments to ensure the quality of the system and the increase in energy efficiency.

Bi-color phosphor-in-glass films achieve superior color quality laser-driven stage spotlights

Laser-driven white lighting sources promise super-high brightness, good directionality and high efficiency, but are usually suffering from low color rendering index (Ra), high correlated color temperature (CCT) and poor light uniformity. To solve these problems, we designed bi-color phosphor-in-glass (PiG) films containing broadband green and red phosphors, and introduced Al2O3 particles as scattering centers into the PiG films. The addition of Al2O3 effectively increases the Ra value from 83 to 93, and greatly improves the angular uniformity in Ra and CCT with Cv(Ra) decreasing from 14.96% to 0.16% and Cv(CCT) decreasing from 45.87% to 1.5%. The coefficient of variation (Cv) is used to evaluate the light uniformity, and the smaller the value, the better the uniformity. The color temperatures can be tuned in a wide range of 2500 ∼ 6300 K by controlling the content of Al2O3 or the ratios of phosphor-to-glass in the films as well as their thicknesses, while high Ra values of > 90 are maintained. A prototype laser-driven white light with excellent color qualities (Ra = 95, Rf = 95, Rg = 104, R9 = 99, R15 = 98) and a high luminous efficacy of 102 lm/W was demonstrated for stage spotlights by optimizing the composition and structure of the bi-color PiG films. This work highlights the roles of secondary phase in heat dissipation and light scattering, and provides ideas to design PiG color converter films for use in super-high color quality laser lighting.

Alkynyl Ligands as Building Blocks for the Preparation of Phosphorescent Iridium(III) Emitters: Alternative Synthetic Precursors and Procedures.

Alkynyl ligands stabilize dimers [Ir(μ-X)(3b)2]2 with a cis disposition of the heterocycles of the 3b ligands, in contrast to chloride. Thus, the complexes of this class—cis-[Ir(μ2-η2-C≡CPh){κ2-C,N-(C6H4-Isoqui)}2]2 (Isoqui = isoquinoline) and cis-[Ir(μ2-η2-C≡CR){κ2-C,N-(MeC6H3-py)}2]2 (R = Ph, tBu)—have been prepared in high yields, starting from the dihydroxo-bridged dimers trans-[Ir(μ-OH){κ2-C,N-(C6H4-Isoqui)}2]2 and trans-[Ir(μ-OH){κ2-C,N-(MeC6H3-py)}2]2 and terminal alkynes. Subsequently, the acetylide ligands have been employed as building blocks to prepare the orange and green iridium(III) phosphorescent emitters, Ir{κ2-C,N-[C(CH2Ph)Npy]}{κ2-C,N-(C6H4-Isoqui)}2 and Ir{κ2-C,N-[C(CH2R)Npy]}{κ2-C,N-(MeC6H3-py)}2 (R = Ph, tBu), respectively, with an octahedral structure of fac carbon and nitrogen atoms. The green emitter Ir{κ2-C,N-[C(CH2tBu)Npy]}{κ2-C,N-(MeC6H3-py)}2 reaches 100% of quantum yield in both the poly(methyl methacrylate) (PMMA) film and 2-MeTHF at room temperature. In organic light-emitting diode (OLED) devices, it demonstrates very saturated green emission at a peak wavelength of 500 nm, with an external quantum efficiency (EQE) of over 12% or luminous efficacy of 30.7 cd/A.

Low-temperature sintering coating of phosphor in TeO2–SiO2–B2O3–ZnO glass for enhanced luminous efficacy of white LED

Low-temperature sintering coating of phosphor in TeO2–SiO2–B2O3–ZnO glass for enhanced luminous efficacy of white LED

Application of luminous efficacies for daylight illuminance data generation in subtropical Hong Kong

PurposeDaylight plays a crucial role in the attainment of building energy savings. Harnessing daylight in building designs will require the need for daylight illuminance data. However, daylight illuminance data are scarce due to few measuring stations. Aside from being sparse, illuminance measuring stations can be expensive to set up, thus making the luminous efficacy model a better alternative. Hence, this study attempted to model horizontal luminous efficacies under the 15 Commission internationale de l'éclairage (CIE) standard skies. Therefrom, daylight illuminance was estimated from a proposed vertical luminous efficacy model.Design/methodology/approachMeasured solar irradiance, daylight illuminance and luminance distribution data were gathered from the local measuring station in Hong Kong. The luminance distribution data were used to classify the skies into the 15 CIE standard skies. Next, the solar irradiance and daylight data were used to derive the horizontal luminous efficacies under each standard sky. Furthermore, a vertical luminous efficacy model developed using the measured data was described, and this was used to predict vertical illuminance.FindingsIt was observed that Skies 1, 8 and 13 seem to be predominant in Hong Kong. Also, the result showed that constant luminous efficacies could be used for deriving illuminance data. Furthermore, horizontal luminous efficacy ranged from 40 to 190lm/W, indicating that daylight can provide sufficient visibility during working hours. The vertical luminous efficacy model proves to offer reasonable estimations of vertical illuminance data.Research limitations/implicationsFurther work needs to be done with more measured data to cover for spring seasons. The described model still needs to be fitted with different world climates to ascertain its universal applicability. The evaluations need to be done under obstructed sky conditions to cater for dense and clustered urban centres.Practical implicationsThe discussed luminous efficacy model could be used to derive illuminance data in the absence of measured daylight illuminance data, especially in the subtropical region. Also, the comparative advantage of daylight over artificial lighting was highlighted in this study.Originality/valueUnlike previous studies, this paper discusses the luminous efficacies of global, direct and diffuse components under the 15 CIE standard skies. Furthermore, the described luminous efficacy analysis provides an approach for deriving vertical and horizontal illuminance data. Such vertical data will be required for analysing building lighting requirements, sensible heat from electric lighting, and energy savings from daylighting controls. Also, the information on horizontal luminous efficacies will help evaluate solar roof and skylight designs.

Blue-green emitting LuASG:Ce phosphor ceramics with high luminous efficacy for high-power LEDs

Phosphor-converted blue-green emitting high-power LEDs (hp-LEDs) are essential for marine fishery and ocean optical communication. Here the blue-green emitting Sc3+-doped LuAG:Ce (LuASG:Ce) phosphor ceramics (PCs), as the phosphor converter of high-power LEDs (hp-LEDs), were successfully prepared by vacuum solid-state sintering based on the engineering of ion substitution. The influences of Sc3+ doping on the structure, optical and luminescence properties of LuAG:Ce were studied in detail. LuASG:Ce PCs owned blue-green emission from 510 nm to 501 nm. The emission intensity at 100 °C maintained more than 85% of the initial one, which exhibited significant thermal stability. Finally, the luminous efficacy (LE) as high as 127.59 lm/W and the emission peak at 503 nm were achieved from the LED encapsulated by Lu2.998Al4ScO12:Ce3+ with 50 W driving power. Thus, the blue-green emitting LuASG:Ce PCs will be promising phosphor converters for hp-LEDs.

Utilization of far-red LED to minimize blue light hazard for dynamic semiconductor lighting

ABSTRACT The blue light hazard (BLH) and luminous efficacy of a source () are associated with the photobiological safety and energy saving of light-emitting diodes (LEDs), respectively. In this study, we used genetic algorithm (GA) to optimize the BLH, , and color rendering parameters of five-chip hybrid white LEDs. Based on the optimal results, we used five-chip LEDs to obtain the hybrid white light. Their peak wavelengths were 461.5 (blue), 523.9 (green), 588.2 (orange), 643.3 (red), and 694.2 nm (far-red), respectively. In practice, the blue light hazard efficiency of radiation (BLHER) of the hybrid white light was less than 0.10, which was lower than half of the most common light sources. The ranged from 51.6 to 115.6 lm/W at correlated color temperature (CCT) from 2700 to 6500 K. On average, the CIE general color rendering index (Ra), CIE special color rendering index for the ninth deep red test sample (R9), ANSI/IES TM-30 color fidelity index (Rf), and color gamut index (Rg) of hybrid white light were 91.3, 87.8, 83.3, and 96.7, respectively. The melanopic efficacy of luminous radiation () was tunable in the range of 0.60 to 1.35 mW/lm. These results demonstrated that we used far-red LEDs to fabricate white light with low BLH and relatively high efficiency.

Thermally Robust Orange‐Red‐Emitting Color Converters for Laser‐Driven Warm White Light with High Overall Optical Properties

AbstractLaser‐driven solid‐state lighting with super‐brightness and compactness is recognized as a promising alternative to white light‐emitting diodes. However, it is quite difficult to achieve laser‐driven warm white light with long‐term stability due to the shortage of robust orange‐ or red‐emitting laser phosphors. In this work, an efficient and thermally robust orange‐red (La,Y)3Si6N11:Ce3+ (LYSN)‐BN phosphor‐in‐glass (PiG) film is proposed to realize warm white light, where h‐BN acts as an optical medium to enhance light scattering, a heat sink to reduce the temperature, and a protective layer to prevent LYSN from oxidation. The “LYSN+15 wt.% BN” PiG film shows an internal quantum efficiency of 70% and a luminance saturation threshold of 12.82 W mm−2, much higher than those without h‐BN (i.e., 57.5% and 7.63 W mm−2). A warm white light lamp fabricated by combining “LYSN+15 wt.% BN” PiG film with blue laser diodes, showing tunable correlated color temperatures (2800–5000 K), has a maximal luminous flux of 740 lm and a luminous efficacy of 133.5 lm W−1, which promises high collimation and penetration lighting in the rainy or foggy weather. By designing a composite orange‐red‐emitting phosphor converter, this work lays a foundation for realizing high quality laser‐driven warm white lighting source.

RGBW lighting systems: Influence of the white LED

People spend most of the time under artificial light sources, so it is important to create a comfortable lighting environment for work and rest. Four-component RGBW systems are the most effective for this. It is needed to create methods for obtaining white light with the specified parameters and choose the most optimal LED components. In this work, the influence of the white LEDs parameters on the resulting white light of the RGBW systems is studied. Two different methods proposed by us earlier for obtaining white light are applied for three RGBW systems with different warm white LEDs. It is shown that the use of white LEDs with a colour rendering index close to 80 is more optimal for most applications. In this case, they provide the resulting white light with the colour rendering index above 90 and luminous efficacy above 130 lm/W.

SrAlSiN3:Eu2+ containing phosphor-in-glass: A color converter for solid state laser lighting

In this work, we report a kind of red emitting phosphor-in-glass (PiG) with low sintering temperature which is more conducive to prevent the denaturation of SrAlSiN3:Eu2+ (SASN:Eu2+) caused by the interface reaction between glass and phosphor. In addition, the PiG contains high content (80 wt%) of phosphor powders, which is beneficial to high power density light excitation. Under the 450 nm excitation the PiG sample showed an internal quantum efficiency value of up to 75.6%, which is close to that of the original powder SASN:Eu2+ (∼82.3%). When driven by a 1 W blue LD, the luminous efficacy of PiG reached 94 lm/W. The glass powder used as the matrix for PiG is borosilicate glass prepared from LTA zeolite and boron oxide. This glass has good optical properties and chemical stability.

Better color distribution uniformity and higher luminous intensity for LED by using a three-layered remote phosphor structure

Abstract Angular color distribution uniformity has been one of the most relevant properties in the development of white light-emitting diodes (WLEDs), since color consistency and uniformity are crucial factors in quality evaluation of a WLED. Here, particularly considering the need to overcome the poor chromaticity usually associated with WLED, we introduce a new design for the remote-phosphor package, namely a three-layered or triple-layer (TL) phosphor structure. Using three phosphor layers in packaging a WLED can result in higher color quality and luminous efficacy, compared to the double-layer (DL) configuration. In the present study, the results of using three remote phosphor layers indicate that although the structure using three layers has a lower color rendering index, the color quality scale is better than that available from the package with two layers. Additionally, the color-deviation values in the TL structure are smaller than in the dual-layer one, especially at high color temperatures (7,700 K and 8,500 K). Besides, in comparison with the DL model, the TL package increases the luminous flux by 1.4%–2%. Therefore, the TL remote phosphor structure possesses the greatest potential in enhancing the WLED quality.

Effect of poly(vinyl alcohol) (PVA) capping agent on structural, photoluminescent and photometric properties of ZnO nanoparticles

ZnO nanoparticles (ZnO NPs) with the hexagonal wurtzite structure were successfully synthesized by the co-precipitation route, and poly(vinyl alcohol) (PVA) was used as a capping agent. The studied results show that the PVA capping agent affects the optical and photometric characteristics of ZnO NPs. PVA-ZnO NPs show the blue emission, the green emission, and the co-emission of yellow and red emissions. The PVA-ZnO NPs possessed the maximum value of the luminous efficacy of optical radiation (LER) LER = 389.52 lm/Wotp and the scotopic/photopic (S/P) S/P = 0.93 at the 1.0 g of PVA, respectively. The color correlated temperature (CCT) and the color CIE (x, y) coordinates are about CCT ≈ 4500 K and (0.36, 0.37), respectively.

Lambertian Luminous Intensity Radiation Pattern Analysis in OLOS Indoor Propagation for Better Connectivity

This paper illustrates the impact of wavelength on the Optical Line of sight (OLOS) link working in the Visible Light Communication (VLC) spectrum. The extension of work is based on previous outcomes given by researchers. It has been elaborated with different determinants based on the color factor of LED available in the Visible Light (VL) spectrum. In the modern world, Light Emitting Diodes (LEDs) are prevailing the market as a light source, which is dominantly used at homes and workplaces. The designed VLC system includes LED as a transmitter, which is used as a higher source of brightness and provides both illuminations and data communication. Solid-state lighting characteristic shows the electroluminance capability of high brightness LEDs. Within few years, the luminous efficacy of LED is exponentially increasing from the range of less than 0.1 lm/W to over 230 lm/W with a huge lifetime of around 100,000 h. MATLAB is used to simulate a VLC link between LEDs (operated at different wavelengths) and photodetector. We present here the performance analysis of Lambertian Luminous Intensity radiation pattern (LLIRP) generated by different colors of LED for a clear OLOS model with different Spectral Luminous Efficiency at photonic vision. A designed system model of VLC supports short links present in indoor room conditions with better connectivity.

An energy transfer strategy for highly luminescent green-emitting Ce3+/Tb3+ codoped Ca2LaHf2Al3O12 garnet phosphors in white light-emitting diodes

Bright, energy-efficient, and stable white lighting sources, such as light-emitting diodes, are desirable to mitigate climate change. A near-ultraviolet-excitable, green-emitting Ca2LaHf2Al3O12:Ce3+,Tb3+ garnet phosphor with high photoluminescence efficiency, prepared by solid-state synthesis, is described. X-ray diffraction Rietveld refinement reveals its garnet structure with space group Ia3¯d and crystallographic parameters a = b = c = 12.528 Å, α = β = γ = 90°, and V = 1966.470 Å3. On 408 nm excitation, it produces bright green light peaking at 543 nm owing to the 5D4→7F5 transition of Tb3+ ions and demonstrates an ultrahigh internal quantum efficiency (80%) and high external quantum efficiency (59.2%). The luminescence intensity of Ca2LaHf2Al3O12:0.05Ce3+,0.6Tb3+ is double that of a Ca2LaHf2Al3O12:0.05Ce3+ green phosphor owing to Ce3+→Tb3+ energy transfer. This Ca2LaHf2Al3O12:0.05Ce3+,0.6Tb3+ green phosphor was used to fabricate a near-UV-pumped white LED device; the resulting luminous efficacy and color rendering index at 3397 K were 17.56 lm/W and 93.1, respectively.

Photoluminescence Properties of AScSi2O6:Cr3+ (A = Na and Li) Phosphors with High Efficiency and Thermal Stability for Near-Infrared Phosphor-Converted Light-Emitting Diode Light Sources.

Near-infrared (NIR) phosphors are fascinating photoluminescence materials with applications in phosphor-converted light-emitting diodes (pc-LEDs) for night vision lighting, which are still restricted by low efficiency and thermal stability in the current research stage. In this work, AScSi2O6 (A = Na/Li) are chosen as hosts due to a larger band gap and a single octahedral site for Cr3+ doping. The NIR-emitting Cr3+-activated AScSi2O6:Cr3+ phosphors were successfully prepared by a common high-temperature solid-state method. X-ray diffraction and Rietveld refinement confirm that the Cr3+ prefers to enter the Sc3+-octahedral lattice site in the AScSi2O6 structure. Under blue light excitation, AScSi2O6:Cr3+ phosphors exhibit broadband NIR emission from 700 to 1100 nm with a full width at half-maximum of ∼150 nm owing to the 4T2 → 4A2 electron transition of Cr3+. The photoluminescence properties were enhanced by adjusting the fluxes and sintering conditions, and highly efficient LiScSi2O6:Cr3+ NIR phosphors with external quantum efficiencies of 33.4% were obtained. Moreover, the optimized LiScSi2O6:Cr3+ exhibits excellent thermal stability (75% at 150 °C) with an activation energy of 0.33 eV. Importantly, the fabricated NIR pc-LED with the highly efficient LiScSi2O6:Cr3+ phosphor demonstrates brighter NIR light and a higher luminous efficacy than the NaScSi2O6:Cr3+ phosphor in night vision.

Surface engineered environment-stable red-emitting fluorides for white light emitting diodes

Poor water stability is the main problem of commercialized Mn 4+ -doped fluorides for white light emitting diode (WLED) application. This work proposes a surface engineering strategy to rebuild a Mn 4+ -free fluoride shell on fluorides to effectively resist the destruction from water molecules. By simple processing using glyoxylic acid (GA) solution, the moisture resistance of the red-emitting fluorides can be significantly improved. The photoluminescence (PL) quantum efficiency (QE) of the surface-engineered K 2 SiF 6 :Mn 4+ (KSFM-GA) still maintain 98.43% after water immersion for 360 h, in sharp contrary to the untreated one (its PLQE decreases to 59.79%). Additionally, PL intensity of the hydrolyzed KSFM can be recovered to 99.1% through the treatment of the reducing GA solution. By using the high-stability KSFM-GA red phosphor, the as-fabricated high-performance warm-WLED device can still maintain 84.6% in luminous efficacy, higher than that (79.6%) with the untreated KSFM, after 500 h of aging in a high temperature (85 °C) and high humidity (85%) environment. • The surface engineering strategy is very simple for processing the commercial fluorides. • The surface reconstructed fluorides well remain the morphology and photoluminescence (PL) properties. • The PL intensity of the surface-engineered fluorides is almost unchanged even after being immersed in water for 360 h. • The reducing glyoxylic acid solution can fully restore the photoluminescence intensity of the hydrated fluorides. • The white-LED device with the surface-engineered fluoride shows improved color stability.