Light-emitting Diode Technology Research Articles

Exploring Illumination and Communication: A Comprehensive Analysis of LED Lighting in Modern Interior Architectural Designs, Enhanced by Weighted Sum Model and Cluster Analysis for Informed Lighting Selection

ABSTRACTThe study of light is crucial in modern interiors, as it dispels darkness and enhances both functionality and aesthetics. From the primal flicker of flames in ancient caves to the advanced light emitting diode (LED) systems of today, lighting has been pivotal in shaping our surroundings and experiences. In contemporary interior architectural designs, lighting fulfills not only functional roles but also greatly influences the aesthetics and atmosphere of a space. Light has been an integral element in sleek interior architecture. With the advancements in LED technology, the approach to illuminating spaces has been transformed providing energy‐efficient solutions. This paper explores the role of LED lighting in modern interior architectural designs focusing on its impact on illumination and communication. Using a weighted sum model and cluster analysis, the various LED lighting configurations are evaluated for their suitability in different spaces. Performance metrics such as illuminance levels, uniformity, adherence to standards, signal‐to‐noise ratio (SNR) and bit error rate (BER) are analyzed. By varying the configurations of LED array per position from 10 × 10 to 100 × 100 the performance across different scales is assessed. The results offer insights for selecting LED lighting options that optimize functionality, aesthetics and energy efficiency in modern interior spaces.

Waste SMD LEDs from End-of-Life Residential LED Lamps: Presence and Characterisation of Rare Earth Elements and Precious Metals as a Function of Correlated Colour Temperature

Energy consumption in buildings is linked to lighting technology. Light-emitting diode (LED) technology includes lamps and luminaires for general lighting applications. Due to their structure, LED lamps are expected to generate specific waste electrical and electronic equipment (WEEE) streams. LEDs are the main source of luminous flux, and their elemental composition is of particular interest to the recycling sector. In this study, surface-mount device (SMD) LEDs from six types of LED lamps (E27, E14, G9, R7S, GU10, and MR16) were removed, collected, separated by correlated colour temperature (CCT) (2700 K, 3000 K, 4000 K, and 6500 K), and characterised for the presence of rare earth elements and precious metals. They were digested with HNO3, aqua regia, and HF in a hot plate and characterised by inductively coupled plasma mass spectrometry (ICP-MS). The concentration of each element as a function of CCT ranged as follows: lanthanum, 242–1840 mg/kg; cerium, 132–284 mg/kg; europium, 15–69 mg/kg; gadolinium, 1.9–3.8 mg/kg; terbium, 0.1–0.4 mg/kg; lutetium, 29–6381 mg/kg; yttrium, 4804–11,551 mg/kg; silver, 2712–5262 mg/kg; gold, 502–956 mg/kg; and palladium, 32–110 mg/kg. These results indicate the need for selective removal and separate recycling processes of SMD LEDs from LED lamps.

Non-Conjugated Gridized Nanopolymers as an Efficient Hole-Transport Material for Blue Perovskite Light-Emitting Diodes.

Despite the remarkable advancements in perovskite light-emitting diode (PeLED) technology, the development of blue PeLEDs has lagged. The primary bottleneck lies in the difficulty of finding hole transport materials (HTMs) that can both match the energy levels of blue perovskite materials and exhibit efficient hole transport performance. Herein, a novel non-conjugated polyethylene carbazole-based polymer (P-AGCz) is developed that has excellent solution processability and serves as an efficient dopant-free HTM for PeLEDs. The flexible non-conjugated polyethylene backbone of P-AGCz provides exceptional film-forming capabilities. Moreover, the A-shaped carbazole-based side chains deepen the HOMO energy level and minimize the recombination energy, enhancing its ability to inject and transport holes within PeLEDs. The PeLEDs employing P-AGCz as a low-cost, dopant-free polymer HTM have attained an external quantum efficiency (EQE) of 3.26%, which is 1.54 times greater than poly(N-vinylcarbazole) (PVK)-based devices, with a brightness enhancement of 584 cdm- 2 over the PVK-based devices. Furthermore, the P-AGCz-based devices exhibit higher current efficiency at lower driving voltages, indicating reduced energy consumption and expanded potential for future applications.

Sustainable illumination: experimental and simulation analysis of illumination for workers wellbeing in the workplace

Incorporating an illumination optimization plan into the worker safety management process in industrials is essential since the quality of workplace illumination has a significant impact on workers' well-being. The purpose of this study was to optimize illumination conditions in industrial workspaces using light-emitting diode (LED) technology with a color temperature of 6500 K and a CRI of 85%. To accomplish this, the DIALux illumination simulation tool was utilized. It was validated using measured illumination data from a lux meter (ST-1300 model 1308). Four factors—the number of luminaires, the effective height of the luminaires, the illumination technology, and the light loss factor—were applied to configure sixteen simulation scenarios. Subsequently, eleven quadratic polynomial equations were proposed for estimating the changes in the average illumination in eleven workplaces using the multiple regression analysis technique on the simulatively prepared dataset. The final step was assessing the desirability degree of the suitable illumination scenario. It was discovered that the DIALux software's illumination simulation error percentage fell within an acceptable range. The illumination technology factor had the greatest impact on the average illumination of workplaces. The most impactful interaction terms of the factors were illumination technology and the number of luminaires. For every workplace, the optimized illumination's desirability degree was expected to be more than 0.9. The proposed approach yields promising results and can be a valuable tool for improving the illumination conditions of workers in industries.

A Review of The Effects Of Light-Emitting Diodes (LEDs) on The Growth of Sunflower Microgreens and Their Nutritional Potential

Sunflower (Helianthus annuus) microgreens have become known as a potent source of essential nutrients and bioactive compounds with numerous health benefits. The microgreens industry has traditionally favored popular microgreens from the Brassicaceae family such as kale, rocket, and broccoli. Sunflower microgreens are characterized by their richness in vitamins, minerals, antioxidants, and phytochemicals that contribute significantly to a nutritious diet. However, their nutrient content can be influenced by various factors, including growing conditions and lighting. Light-emitting diodes (LEDs) offer precise control of light spectrum, light intensity, and lighting duration, enabling customized lighting systems optimized for growing sunflower microgreens. Pre-treatment and optimal harvest timing affect the quality and yield of microgreens, and sunflower microgreens are no exception. Accordingly, sunflower microgreens are typically harvested within 7 days of cultivation, making them ideal for mass production. The use of LED technology in the cultivation of microgreens offers the opportunity to further enhance their nutritional value and therapeutic potential. This review provides an overview of the benefits of sunflowers, sunflower microgreens, pre-treatments, and the ideal harvest period. The potential improvements from LED lighting are discussed and its impact on human health is explained.

Efficient and Stable Deep-Blue 0D Copper-Based Halide TEA2Cu2I4 with Near-Unity Photoluminescence Quantum Yield for Light-Emitting Diodes.

Achieving deep-blue light with high color saturation remains a critical challenge in the development of white light-emitting diode (LED) technology, necessitating luminescent materials that excel in efficiency, low toxicity, and stability. Here, we report the synthesis of [N(C2H5)4]2Cu2I4 (TEA2Cu2I4) single crystals (SCs), which exhibit deep-blue photoluminescence (PL) at 450 nm. These crystals are characterized by a significant Stokes shift of 180 nm, a long lifetime of 1.7 μs, and an impressive photoluminescence quantum yield (PLQY) of 96.7% for SCs and 87.2% for polycrystalline films. The zero-dimensional structure is attributed to the proper spacing of triangular inorganic units [Cu2I4]2- by organic cations [N(C2H5)4]+. This structural arrangement facilitates broadband deep-blue light emission with phosphorescent characteristics, as evidenced by temperature-dependent PL and time-resolved photoluminescence (TRPL) measurements. The band gap properties of TEA2Cu2I4 were further elucidated through density functional theory (DFT) computations. Notably, the material exhibited minimal PL intensity degradation after continuous UV irradiation and one month of exposure to ambient conditions. Moreover, the polycrystalline film of TEA2Cu2I4 maintained substantial deep-blue emission even after one year of storage. Utilizing TEA2Cu2I4 thin film, we fabricated an electroluminescent device emitting deep-blue light with high color saturation, featuring CIE coordinates (0.143, 0.076) and a brightness of 90 cd/m2. The exceptional photophysical properties of TEA2Cu2I4 render it a highly promising candidate for optoelectronic applications.

IGZO TFT Backplane Integration for µLED Flat-Panel Display

Display technologies have continuously evolved since the advent of cathode ray tube (CRT) displays in the early 1900s. Thanks to modern advancements, current display thicknesses are on the order of centimeters and their area has increased 10-fold. Modern flat panel display (FPD) systems consist of a TFT backplane that controls the filtering of a backlight or the modulation of emissive devices such as OLED or microLEDs (µLEDs). MicroLED technology is favored over organic light-emitting diode (OLED) technology due to its higher brightness, energy efficiency, and longer operational lifetime. Additionally, µLEDs offer small pixel sizes, scalability to large screen sizes, and increased durability compared to OLEDs. While both technologies have their strengths and weaknesses, the choice between them depends on specific application requirements and preferences.The primary focus of this work is the process integration of Indium Gallium Zinc Oxide (IGZO) transistors as a µLED backplane for row/column addressing. A single pixel is composed of a µLED driven by an arrangement of two transistors and a storage capacitor. The pixels are then arrayed on a glass substrate to support active-matrix control of monochrome and full color (RGB) displays from 1x1cm (50 x 50 pixels) up to 7.6 x 7.6 cm (380 x 380 pixels). Optimization of circuit parameters considering size and scan frequency was modeled using existing TFT and µLED electrical device compact models. New process parameters and procedures were determined for the proper integration of µLEDs in an existing TFT fabrication process.Red, green, and blue µLED devices were fabricated at Tyndall National Institute on native substrates and were transferred to TFT pixels using an X-Display MTP-1003 micro-transfer printer. The performance of individual test cells was assessed using an Agilent B1500, revealing a voltage transfer characteristic indicating the ability to modulate and control µLED current. Techniques were investigated for the system integration of the active matrix with control circuitry. Figure 1

Enhancing energy efficiency in Bangladesh’s readymade garment sector: the untapped potential of LED lighting retrofits

Purpose Previous studies emphasized the substantial energy-saving potential of light emitting diode (LED) lighting systems, especially in the clothing industry. However, the specific quantification of energy conservation potential in industrial factories, particularly in Bangladesh’s readymade garment (RMG) sector, remains unexplored. The purpose of this study is to investigate the potential energy savings and efficiency improvements of lighting systems in Bangladesh’s RMG sector using LED technology. Design/methodology/approach Understanding and optimizing energy consumption is crucial in the RMG sector because this sector contributes significantly to the country’s export earnings. For this, an RMG factory was surveyed and possible lighting system retrofitting was estimated and compared. Findings The adoption of energy-efficient lighting options, particularly LED, could decrease the current lighting energy usage from 15% to 7.5% in Bangladesh. First, this study reveals, that the reduction of annual energy consumption was determined to be 18,220 kWh due to the retrofitting of the lighting system with LED tube. Second, it conducts real-time measurements to assess the suitability of in-building lighting systems, providing insights into the current scenario. Lastly, it evaluates the economic and environmental benefits of the proposed lighting system in the RMG industries. Due to the retrofitting of the lighting system, the reduction of equivalent CO2 gas emissions was found to be 119.896 tCO2. Originality/value For the first time, this study explored the potential for enhancing energy-efficient lighting system design through retrofitting in the RMG industry, with a focus on Bangladesh. By addressing these aspects, this study aims to contribute to the advancement of energy efficiency and conservation efforts in the RMG sector, ultimately fostering sustainable industrial development in Bangladesh and beyond.

Improving Inoculum Production of Arbuscular Mycorrhizal Fungi in Zea mays L. Using Light-Emitting Diode (LED) Technology

A substrate-based production system is a simple and low-cost method for arbuscular mycorrhizal (AM) fungal inoculum production. However, it is time-consuming and typically yields low numbers of AM fungal spores due to several factors affecting plant growth efficiency. Our study investigated the use of light-emitting diode (LED) technology to expedite AM fungal spore production in planta. We performed experiments with Rhizophagus irregularis inoculated in maize (Zea mays L.), contrasting LED light with greenhouse (GH) conditions. Our results exhibited a significant improvement in AM fungal colonization and spore production, as well as a reduction in the production period from 120 to 90 days under the LED light condition. This was achieved using a red-and-blue light ratio of 60:40 with a total light intensity of 300 µmol m−2 s−1. The LED light treatments improved maize growth by increasing nitrogen (N) and phosphorus (P) concentrations in shoots and roots, respectively. Our gene expression analyses revealed that in AMF-inoculated plants, genes related to photosynthesis were significantly upregulated under LED light compared to the GH condition. Moreover, LED increased the expression of marker genes linked to the AM fungi-related cell cycle, indicating enhanced AM fungal growth during symbiosis. These findings advance our comprehension of LED applications in agriculture, offering promising prospects for acceleration of AM fungal spore production.

Effects of dim-evening lighting optimised for geographical orientation versus standard lighting on mental health: protocol paper for a quasiexperimental study in a psychiatric hospital

IntroductionResearch has provided novel insights into how light stimulates circadian rhythms through specialised retinal ganglion cells to the suprachiasmatic nucleus. In addition, there has been a revolution in light-emitting diode...

A Cr3+-Yb3+ co-doped high-efficiency near-infrared luminescent phosphor for NIR-II light source applications

Phosphor conversion light-emitting diode (PC-LED) technology has become a focal point of research for portable near-infrared light sources in recent years. One of the crucial aspects is to develop phosphor materials that can be effectively stimulated by commercial available blue light. Unfortunately, efficient phosphors in the NIR-II that can be excited by commercial blue light are particularly scarce. In this study, Mg4Ta2O9:0.04Cr3+,0.03Yb3+,0.07Li+ (MTO:0.04Cr3+,0.03Yb3+,0.07Li+) phosphor was synthesized using the high temperature solid phase method, and its emission spectrum covered the first and second near-infrared windows (700–1200 nm). The internal quantum efficiency (IQE) and external quantum efficiency (EQE) are 88.7 % and 45.6 %, respectively, due to the synergistic effect of energy transfer and Li-ion modification. Additionally, the doping of Yb3+ ions and Li+ ions enhances the thermal stability of luminescence. The thermal stability of MTO:0.04Cr3+,0.03Yb3+,0.07Li+ and MTO:0.04Cr3+,0.03Yb3+ is 9.81 % and 14.43 % higher, respectively, than that of MTO:0.04Cr3+,0.03Yb3+ and MTO:0.04Cr3+. To evaluate its potential applications, we developed a prototype PC-LED utilizing MTO:0.04Cr3+,0.03Yb3+,0.07Li+ phosphor as an emission emitter which demonstrated advantages in biomedical imaging, night vision, and non-destructive testing.

Advances in High-Efficiency Blue OLED Materials

Organic light-emitting diode (OLED) technology has rapidly emerged in the display and lighting sectors due to its high contrast ratio, wide viewing angle, and sleek design. Beyond these attributes, OLEDs have also demonstrated crucial applications in medicine, fashion, sports, and more, leveraging their emissive properties and flexible design. As the cornerstone of full-color displays, blue OLEDs, whose performance directly impacts color rendition and saturation, have garnered significant attention from both scientific researchers and industrial practitioners. Despite the numerous advantages of OLED technology, blue OLEDs still confront formidable challenges in terms of luminous efficiency, durability, and material stability. This review examines the evolution of blue OLED materials over recent years, specifically focusing on three generations: fluorescent, phosphorescent, and thermally activated delayed fluorescence (TADF). Through molecular design, device structure optimization, and the application of innovative technologies, remarkable advancements have been achieved in enhancing the luminous efficiency, lifetime, and color purity of blue OLEDs. However, to advance commercialization, future efforts must not only ensure high efficiency and long lifetime but also improve material stability, environmental sustainability, and reduce development costs. Emerging materials such as thermally activated exciton materials and the application of hyperfluorescent (HF) OLED technology represent vital driving forces for the continuous advancement of blue OLED technology. It is anticipated that significant milestones will continue to be achieved in the development of highly efficient blue OLEDs in the future.

Inactivation of Hepatitis A Virus and Feline Calicivirus on Model Food Contact Surfaces by Ultraviolet Light (UV-C) Systems.

Food contact surfaces can harbor and transmit pathogens leading to outbreaks. Decontamination strategies that are user- and environmentally-friendly without toxic by-product formation are needed. Novel UV-C light-emitting diode (LED) technologies are being explored to deliver the required dose to inactivate viruses in food-processing environments. The objective of this study was to compare the effects of 279 nm UV-C LED to 254 nm UV-C against hepatitis A virus (HAV) and feline calicivirus (FCV, a cultivable human norovirus surrogate) on stainless-steel, ceramic, and glass surfaces. Viruses were surface spread on sterile stainless-steel or ceramic coupons (100 μL on 2 × 2 cm2), or glass discs (50 μL on 1 × 1 cm2), air-dried, and UV-C-treated for up to 3.75 min (surface dose = 0-49.2 mJ/cm2 for HAV and 0-24.6 mJ/cm2 for FCV). Each triplicate treatment was assayed in duplicate, and data were statistically analyzed. The D10-values for HAV treated with UV-C at 254 nm on stainless-steel, ceramic, and glass were 9.48 ± 0.34, 14.53 ± 2.52, and 6.91 ± 1.93 mJ/cm2, while with UV-C LED at 279 nm were 19.53 ± 2.45, 26.05 ± 0.60, and 8.77 ± 2.08 mJ/cm2, respectively. The D10-values for FCV treated with UV-C at 254 nm on stainless-steel, ceramic, and glass were 3.65 ± 0.06, 6.25 ± 1.90, and 4.69 ± 0.03 mJ/cm2, while with UV-C LED at 279 nm were 7.097 ± 2.11, 8.31 ± 2.12, and 7.88 ± 0.86 mJ/cm2, respectively. Higher 279 nm UV-C doses were needed to inactivate HAV and FCV compared to 254 nm UV-C on the tested surfaces. Novel UV-C LED systems using appropriate doses show promise to inactivate foodborne viruses on food contact surfaces.

Light Quality Influence on Growth Performance and Physiological Activity of Coleus Cultivars

This study investigates the influence of different light qualities, including red, green, blue, purple, and white lights, on the growth, physiological activity, and ornamental characteristics of two Coleus cultivars. Emphasizing the importance of leveraging phenotypic plasticity in plants within controlled environments, using light quality is a practice prevalent in the ornamental industry. The research explores the varied responses of two Coleus cultivars to distinct light spectra. The key findings reveal the efficacy of red light in enhancing shoot and leaf parameters in C. ‘Highway Ruby’, while red and green light exhibit comparable effects on shoot width and leaf dimensions in C. ‘Wizard Jade’. White light-emitting diodes (LEDs), particularly with color temperatures of 4100 K and 6500 K, promote root length growth in the respective cultivars. Moreover, chlorophyll content and remote sensing vegetation indices, including chlorophyll content (SPAD units), the normalized difference vegetation index (NDVI), the modified chlorophyll absorption ratio index (MCARI), and the photochemical reflectance index (PRI), along with the chlorophyll fluorescence, were significantly affected by light qualities, with distinct responses observed between the cultivars. In summary, this study highlights the transformative potential of LED technology in optimizing the growth and ornamental quality of foliage plants like Coleus, setting a benchmark for light quality conditions. By leveraging LED technology, producers and nursery growers access enhanced energy efficiency and unparalleled versatility, paving the way for significant advancements in plant growth, color intensity, and two-tone variations. This presents a distinct advantage over conventional production methods, offering a more sustainable and economically viable approach for increased plant reproduction and growth development. Likewise, the specific benefits derived from this study provide invaluable insights, enabling growers to strategically develop ornamental varieties that thrive under optimized light conditions and exhibit heightened visual appeal and market desirability.

A comprehensive survey on an IoT-based smart public street lighting system application for smart cities

The swift advancement and updating of urban lighting systems, along with the incorporation of smart and Internet of Things (IoT) infrastructure, have opened up numerous opportunities for technological progress across various facets of life. This paper offers a comprehensive overview on the development of smart public street lighting infrastructure tailored for IoT applications in smart cities. Initially, the focus lies on transitioning from conventional lighting to Light-Emitting Diodes (LEDs) technology in street lighting. Complementing this transition, the incorporation of the wireless networked sensors and controllers ensures dynamic brightness control in operational zones, envisioning substantial energy savings. Furthermore, the notion characterizing smart cities denotes incorporating modern digital infrastructures to develop innovative functionalities and connect various application, following the IoT paradigm. The key findings from the proposed study have enhanced knowledge regarding smart public street lighting application. This system integrates smart poles equipped with LEDs lamps technology, smart sensors, communication network and monitoring unit, leveraging current technological advancements in IoT applications. The implementation of IoT-based smart public street lighting systems presents several challenges, including integrating diverse sensors and actuators ensuring robust device communication, secure data management, and effective system scaling and maintenance. Despite these challenges, this system significantly advances smart city infrastructure by enhancing energy efficiency, safety, and sustainability. However, addressing their high initial costs, data privacy and security concerns, and ongoing maintenance are crucial in future studies to realize their full potential in smart cities.

Study of structural, elastic, electronic, optical, magnetic and thermoelectric characteristics of Hexafluoromanganets A2MnF6 (A = Cs, Rb, K) cubic double perovskites

We analyse a detailed investigation of structure, electronic, optical, magnetic and thermoelectric properties of (Cs, Rb, K)2MnF6 double perovskites with cubic Fm3¯m space group. The calculation method was the augmented plane-wave functions plus local orbitals as implemented in the WIEN2k code and the GGA followed by the most accurate GGA-mBJ as exchange potentials. The precision of our K2MnF6, Rb2MnF6 and Cs2MnF6 lattice constant compared with their available experimental data is in the range 1.2 % to 3.6 %. The calculated band gap of K2MnF6, Rb2MnF6 and Cs2MnF6 materials advantages them for use in light-emitting diode technology. These materials exhibit ferromagnetic behavior. The negative formation energy, free Helmholtz energy and the dispersion of phonons confirm their thermal, thermodynamic and dynamic stability. The calculated band gap of K2MnF6, Rb2MnF6 and Cs2MnF6 materials advantages them for use in light-emitting diode technology. The p-type charge carriers, direct band gap, and flat conduction and valence bands make them as good thermoelectric materials. The major contribution to the magnetization comes from the unfilled Mn-3d orbital. The high static dielectric constant reduces the recombination rate of charge carriers and the presence of absorption peaks in the ultraviolet region are advantageous in the exploitation in the optoelectronic field. The flat valence and conduction bands, high p-type conductivity, good thermoelectric parameters, as well as non-toxicity make these compounds mainly attractive in the thermoelectric application.

Improving luminescence response in ZnGeN2/GaN superlattices: defect reduction through composition control

Color-mixed (cm) light-emitting diodes (LEDs) are theoretically the most efficient white light emitters, projected to improve white light luminous efficacy by 34% compared to incumbent phosphor converted LEDs. Since white light technology is pervasive and essential, small improvements in LED technology can result in energy savings. However, cm-LEDs are not yet realized due to poor efficacy in green and amber emitting materials, a spectral region colloquially referred to as the Green Gap. ZnGeN2 is nearly isostructural and closely lattice-matched to GaN and can be heteroepitaxially integrated with existing GaN devices; ZnGeN2/GaN hybrid structures are theorized to emit green (~530 nn) light with a spontaneous emission rate 4.6–4.9 times higher than traditional InGaN LEDs when incorporated into III-N LED structures. In this report we demonstrate the molecular beam epitaxy (MBE) growth of GaN and ZnGeN2 superlattices, an important step towards realizing multiple quantum well structures required for efficient LEDs. Elemental analysis, including atom probe tomography, shows that Ga and Ge are observed in both ZnGeN2 and GaN layers, degrading the structural uniformity. The lack of elemental abruptness also leads to increased defect luminescence and reabsorption of band edge luminescence. The source of unintentional Ga distributed throughout the ZnGeN2 layers was identified as excess flux escaping from around the closed MBE shutter. The source of unintentional Ge, which tended to incorporate as a single delta-doped layer in GaN, was identified as Ge riding along the cyclical metal-rich Ga adlayer used for high quality GaN, incorporating during subsequent nitrogen-rich growth step. Modifying the growth strategy results in improved structural quality, elemental abruptness, and luminescence response. This realization of structurally and elementally abrupt interfaces demonstrates the potential of heteroepitaxially integrated binary and ternary nitrides for energy-relevant devices.

Atomistic Origins of Various Luminescent Centers and n-Type Conductivity in GaN: Exploring the Point Defects Induced by Cr, Mn, and O through an Ab Initio Thermodynamic Approach.

GaN is a technologically indispensable material for various optoelectronic properties, mainly due to the dopant-induced or native atomic-scale point defects that can create single photon emitters, a range of luminescence bands, and n- or p-type conductivities. Among the various dopants, chromium and manganese-induced defects have been of particular interest over the past few years, because some of them contribute to our present-day light-emitting diode (LED) and spintronic technologies. However, the nature of such atomistic centers in Cr and Mn-doped GaN is yet to be understood. A comprehensive defect thermodynamic analysis of Cr- and Mn-induced defects is essential for their engineering in GaN crystals because by mapping out the defect stabilities as a function of crystal growth parameters, we can maximize the concentration of the target point defects. We therefore investigate chromium and manganese-induced defects in GaN with ab initio methods using the highly accurate exchange-correlation hybrid functionals, and the phase transformations upon excess incorporation of these dopants using the CALPHAD method. We also investigate the impact of oxygen codoping that can be unintentionally incorporated during crystal growth. Our analysis sheds light on the atomistic cause of the unintentional n-type conductivity in GaN, being ON-related. In the case of Cr doping, the formation of CrGa defects is the most dominant, with an E +/0 charge transition at E VBM + 2.19 eV. Increasing nitrogen partial pressure tends to enhance the concentration of CrGa. However, in the case of doping with Mn, several different Mn-related centers can form depending on the growth conditions, with MnGa being the most dominant. MnGa possesses the E 2+/+, E +/0, and E 0/- charge transitions at 0.56, 1.04, and 2.10 eV above the VBM. The incorporation of oxygen tends to cause the formation of the MnGa-VGa center, which explains a series of prior experimental observations in Mn-doped GaN. We provide a powerful tool for point defect engineering in wide band gap binary semiconductors that can be readily used to design optimal crystal growth protocols.

Multireference Ab Initio Calculations on Excited Electronic States of Carbazole-Based Organic Compounds for Thermally Activated Delayed Fluorescence.

The emerging technology of organic light-emitting diodes takes advantage of the thermally activated delayed fluorescence (TADF) mechanism for improved efficiency. Carbazole-based organic molecules are suitable for TADF emission because of charge transfer excitations between the electron-donor carbazole and an electron-acceptor unit. Computational design of new TADF molecules with the desired properties is challenging because charge-transfer excitations cannot be predicted accurately by time-dependent density functional theory. Four groups of carbazole-based donor-acceptor molecules have been studied using multireference ab initio methods to understand the nature of excited electronic states. The state-averaged complete active space self-consistent field (SA-CASSCF) and the N-electron valence state perturbation theory (NEVPT2) were used to calculate energies and oscillator strengths for multiple excited electronic states. The number of active electrons and orbitals and the number of excited states included in state-averaged CASSCF were selected such that the accuracy of ab initio predictions could be improved systematically. The procedure introduced here for the calculation of multiple excited electronic states of TADF candidates can be used to accelerate the computational search for efficient TADF materials.

Efficient and stable hybrid perovskite-organic light-emitting diodes with external quantum efficiency exceeding 40 per cent

Light-emitting diodes (LEDs) based on perovskite semiconductor materials with tunable emission wavelength in visible light range as well as narrow linewidth are potential competitors among current light-emitting display technologies, but still suffer from severe instability driven by electric field. Here, we develop a stable, efficient and high-color purity hybrid LED with a tandem structure by combining the perovskite LED and the commercial organic LED technologies to accelerate the practical application of perovskites. Perovskite LED and organic LED with close photoluminescence peak are selected to maximize photon emission without photon reabsorption and to achieve the narrowed emission spectra. By designing an efficient interconnecting layer with p-type interface doping that provides good opto-electric coupling and reduces Joule heating, the resulting green emitting hybrid LED shows a narrow linewidth of around 30 nm, a peak luminance of over 176,000 cd m−2, a maximum external quantum efficiency of over 40%, and an operational half-lifetime of over 42,000 h.