Light-emitting Diode Chip Research Articles

Solid-State White Light-Emitting Diodes Based on 3D-Printed CsPbX3-Resin Color Conversion Layers

Inorganic metal halide-based perovskites have tremendous potential for use in solid-state lighting due to their earth-abundant elements, solution processability, high photoluminescence quantum yield (PLQY), and tunable band gap energy and emission. However, the stability issue remains a challenge. Here, we report the use of a 3D printing technique to fabricate resin-perovskite color conversion layers to bridge the gap between material development and device applications. This not only simplified the fabrication process but also significantly improved the performance of the device. By using an economic 3D printer, color-emitting perovskite nanocrystals (green, yellow, and red) were mixed with highly transparent UV resin to obtain a thin color conversion layer. These 3D-printed color conversion layers retained above 80% of their original PLQY after 180 days of storage in ambient conditions, confirming their exceptional stability. Furthermore, we stacked the printed color conversion layers on top of the UV light-emitting diode chip, resulting in white lights with tunable correlated color temperatures, high color rendering indexes up to 94, color coordinates of (0.32, 0.33) close to the standard neutral white light, and high luminous efficacy of radiation up to 299 lm/W. As a result of this work, the adoption of solid-state lighting on a broader scale will be one step closer to reality.

High luminous efficiency of a phosphor-in-glass plate by optimization of the glass and phosphor content for high-power LED applications

Generally, white light-emitting diodes (LEDs) are fabricated by combining blue LED chips with yellow phosphors. When fabricating white LEDs, the phosphor is typically mixed with an organic resin and applied to the LED chips as a paste. A phosphor-in-glass (PiG) plate can alternatively be used to address the poor high-temperature reliability of the paste method. However, because pores form in the PiG plate during the sintering process, this method results in a loss of optical efficiency. Accordingly, we aimed to improve the fluidity of glass and light efficiency by optimizing the sintering temperature of the glass powder and the phosphor content respectively for reducing internal porosity in the PiG. In this study, glass powder was sintered at different temperatures to produce glass plates, while also varying the phosphor content to fabricate PiG plates. The optimal light characteristics were realized with a glass sintering temperature of 640 °C and a phosphor content of 20 wt%.

Effect of Phase Change Materials on the Optical Path of LEDs for Opto-Thermal Enhancement

A novel concept based on the encapsulation of transparent phase change materials (PCMs) into the optical packaging structure of light-emitting diodes (LEDs) is presented in this article. The concept was initiated by challenges of thermal management of photoluminescent particles in high-power optical systems. LEDs, white LEDs (WLEDs), and porous/network-based photoluminescent matrices can achieve improved thermal networks by embedding PCMs. In this article, paraffin is selected as a suitable PCM encapsulant, and aside from thermal perspectives, an unexpected optical benefit with melted paraffin after surface wetting of the chip was observed. Immersing an LED chip in a melted paraffin pool showed up to an 8% increase in light extraction efficiency and a 1.5% increase in power conversion efficiency (PCE). An accurate dynamic opto-electro-thermal monitoring of studied devices was used to support the proof of concept. This viable method can be integrated into current industrial packaging processes.

Anisotropic graphene films with improved thermal conductivity and flexibility for efficient thermal management

The rapid development of miniaturization and densification of electronic devices brings substantive needs for highly thermally conductive and flexible thermal interface materials (TIM) to ensure service reliability and prolong the lifetime of electronic components. Herein, we proposed highly thermally conductive and flexible graphene (Gr) films by a vacuum-assisted filtration strategy. Driven by the strong vacuum shear force and the dispersing effect of Polyvinyl pyrrolidone (PVP), the Gr sheets stacked layered-by-layered owing to hydrogen bond (H-bond). The highly laminated Gr/PVP films (GPVP-F) exhibited high in-plane thermal conductivity of 81.2 W m−1 K−1 and through-plane thermal conductivity of 5.1 W m−1 K−1. In actual applications, the GPVP-F cooled the light-emitting diode (LED) chip by 4.3 °C (from 46.1 °C to 41.8 °C) when being used as flexible TIM, which was at an advanced level for room-temperature device (＜ 50 °C) cooling. Besides, GPVP-F still performed excellent thermal conductivity (68.1 W m−1 K−1) even at 100 °C and splendid stability after 10 times of heating-cooling cycles. More importantly, the meritorious flexibility ensured GPVP-F being capable of applying in the device with irregular shapes. All the above results bring GPVP-F a promising prospect in thermal management of electronic devices.

Solvent-free rapid synthesis of carbon nanodots at atmospheric pressure: Preparation of transparent light conversion films with ultrahigh efficient UV and blue light shielding

In this age of technology, people are inevitably surrounded by electronic devices and light-emitting devices, but the radiation generated by these devices is very harmful to humans. Therefore, it is crucial to develop a stable absorbing material with efficient absorption capacity for UV and high-energy blue light (HEBL). In this paper, we report that carbon nanodots (CDs) with strong absorption peaks in the UV and HEBL can be rapidly synthesized in large scale by simply heating urea and citric acid at high temperature under atmospheric pressure without using any solvents. Interestingly, the large-scale prepared CDs possess green fluorescence emission upon excitation in both the UV and HEBL regions, exhibiting good photoconversion ability. Furthermore, ultrahigh efficient UV and HEBL shielding films can be prepared by embedding the CDs in a carboxymethyl cellulose matrix. By characterizing their transmission and absorption spectra, it can be found that the cellulose films containing 0.2 wt% CDs achieve almost complete shielding of UV-A, UV-B, and HEBL with a guaranteed visible light (550 nm) transmission rate of 80% or above. Finally, this cellulose film was further attached to a light-emitting diode (LED) chip to investigate its practical use in the field of UV and strong blue light shielding.

High-efficiency flat-type nitride-based micro-light emitting diodes using local breakdown conductive channel

A flat-type p-p light-emitting diode (LED) utilizing a local breakdown conductive channel (LBCC) in nitride semiconductor-based LEDs is introduced to replace n-p LEDs with existing mesa etched structures. The flat-type p-p LED, including the LBCC, exhibits similar light output power in the same injection current as the n-p LED of the conventional mesa structure but at a higher operating voltage. Consequently, the flat-type p-p LED with LBCC has lower wall plug efficiency compared to the mesa structured n-p LED. However, when the LED size is small, the flat-type p-p LED can achieve an optical power and operating voltage similar to the conventional n-p LED. As the LED size decreases, the n-type electrode of mesa-type n-p LED decreases to the similar size to the LBCC, providing an alternative to the operating voltage characteristics and wall plug efficiency. In addition, the junction temperature of the LED decreases as the LED size decreases. Based on these results, it is believed that the flat-type P-P LED can be advantageous for achieving high efficiency in smaller LED chips due to the smaller dry-etched mesa area which contains crystal defects that act as non-radiative recombination centers, and higher heat dissipation capacity.

P‐11.5: Design and Optimization Polarized Light Emitting Diode Chips with Nano‐Wire Grid Polarizer and Meta‐surface Textures

A low power consumption is one of the most important issue for all of the electrical products, especially for wearable products. This manuscript proposed a polarized light emitting diode (LED) chip which is used for a direct back light unit for LCD. A wire grid polarizer and a meta-surface textures are set on the top and bottom of the LED chip in order to obtain a high polarization ratio and transparency. After optimizing the potential parameters, the transmittance of TM and the polarization can reach up to 93.71% and 99.3% respectively. It can replace the normal LED in direct back light unit, and obtain an improved efficiency of 20%, when comparing liquid crystal display with a bottom APF polarizer. It can be used for reducing power consumption and supply dependence, as well as the cost of displays.

Highly efficient photonic PCR system based on plasmonic heating of gold nanofilms

The polymerase chain reaction (PCR) is a standard molecular method that has the potential to solve the need for accurate, viable, and immediate infectious pathogen detection at point-of-care (POC) centers in different fields such as pathogen identification, and forensics. In this work, we present a photonic PCR thermocycler that achieves strong optical absorption, more efficient gene amplification, and further improves the effect of temperature distribution through the PCR sample using two gold nanofilms (AuNFs) and a high-power light-emitting diode chip (LED). The photonic device achieved higher heating and cooling rates of 13.20 null°C/s and 7.92 null°C/s, respectively on average, with uniform and reliable temperature distribution throughout the sample with negligible deviations. During amplification cycles, maximum temperatures attained had variations less than 1 °C at 90 °C, less than 0.8 °C at 55 °C, and less than 0.5 °C at 72 °C, showing uniform heating which yielded more accurate and reliable results. Using the fabricated device, PCR amplification for a bacteria genomic DNA was performed in 7.5 minutes for 30 thermal cycles with a sample volume of 20 μL. Due to the device's simple configuration and increased heat transfer rates, this photonic platform will be a highly efficient choice for rapid POC applications in developing countries.

Single-chip horticultural LEDs enabled by greenly synthesized red-emitting carbon quantum dots

Light emitting diodes (LEDs) having the emission spectra that match the absorption regions of a target plant are strongly demanded for vertical farming. Herein, we demonstrate the use of red-emitting carbon quantum dots (R-CQDs) as a phosphor to fabricate cost-effective horticultural LEDs. R-CQDs having chlorophyll molecules embedded in a carbogenic matrix were solvothermally synthesized using ethanol extract of bougainvillea leaves as a green carbon source. R-CQDs emit a narrow band maximizing at 670 nm originated from the chlorophyll centers when excited either the carbogenic matrix or embedded chlorophyll. R-CQD phosphor converts partially 410 nm light emitted from a LED chip to red and far red regions, thus offering cheaper, single – chip LEDs for agriculture lighting.

Broadband Near-Infrared Luminescence in Garnet Y3Ga3MgSiO12: Cr3+ Phosphors.

Broadband near-infrared (NIR) phosphors are the critical component of phosphor converted NIR light-emitting diode (LED) light sources. However, there are still a lack of NIR phosphors with excellent external quantum efficiency (EQE) and thermal stability. Here, we report a highly efficient broadband NIR phosphor Y3Ga3MgSiO12: Cr3+. The optimized phosphor yields an internal quantum efficiency (IQE) and an EQE of 79.9 and 33.7%, respectively. The integrated emission intensity still remains at 84.4% of that at room temperature when heated to 423 K. A broadband NIR LED lamp was made by combining as-prepared phosphor and a blue InGaN LED chip, which shows an output power of 89.8 mW with a photoelectric conversion efficiency of 17.1% driven at 525 mW input power. Our research provides a promising NIR phosphor with high efficiency broadband for the NIR light source.

Arrays of TiO2 Nanosphere Monolayers on GaN-Based LEDs for the Improvement of Light Extraction

We report on the fabrication of TiO2 nanosphere (NS) monolayer arrays for the enhancement of light extraction quantum efficiency of GaN-based light-emitting diodes (LEDs). The fabricated TiO2 NSs monolayer arrays were composed of different phases of anatase (An-) and amorphous (Am-) TiO2. The arrays were transferred onto the topmost layer of LED chips via the facile icing transfer method. The LED chips covered with Am-TiO2 NS monolayer arrays showed 3.0- times enhanced light output power intensity compared with reference LED chips at a fixed injection current of 100 mA. The enhanced light extraction of LED chips by an Am-TiO2 NS monolayer can be attributed to a high transmittance (91.1%) in visible and increased light extraction probability of photons generated in LEDs, resulting from the enhanced light coupling efficiency by reduced total internal reflection (TIR). Finite-difference time-domain (FDTD) simulation results also agreed well with the experimentally observed results. Based on the experimental and theoretical results, our suggested Am- and An-TiO2 NS arrays can be considered a very facile and effective method to improve the device performance of various visible LED chips.

Realizing Wide‐Gamut Human‐Centric Display Lighting with K3AlP3O9N:Eu2+

AbstractComputers, televisions, and smartphones are revolutionized by the invention of InGaN blue light‐emitting diode (LED) backlighting. Yet, continual exposure to the intense blue LED emission from these modern displays can cause insomnia and mood disorders. Developing “human‐centric” backlighting that uses a violet‐emitting LED chip and a trichromatic phosphor mixture to generate color images is one approach that addresses this problem. The challenge is finding a blue‐emitting phosphor that possesses a sufficiently small Stokes’ shift to efficiently down‐convert violet LED light and produce a narrow blue emission. This work reports a new oxynitride phosphor that meets this demand. K3AlP3O9N:Eu2+ exhibits an unexpectedly narrow (45 nm, 2206 cm−1), thermally robust, and efficient blue photoluminescence upon violet excitation. Computational modeling and temperature‐dependent optical property measurements reveal that the narrow emission arises from a rare combination of preferential excitation and site‐selective quenching. The resulting chromaticity coordinates of K3AlP3O9N:Eu2+ lie closer to the vertex of the Rec. 2020 than a blue LED chip and provides access to ≈10% more colors than a commercial tablet when combined with commercial red‐ and green‐emitting phosphors. Alongside the wide gamut, tuning the emission from the violet LED and phosphor blend can reduce blue light emissions to produce next‐generation, human‐centric displays.

Red–NIR Luminescence in Rare-Earth and Manganese Ions Codoped Cs4CdBi2Cl12 Vacancy-Ordered Quadruple Perovskites

Combining rare-earth ions (RE3+) in halide perovskites is a hopeful strategy to produce interesting optical properties in visible and near-infrared (NIR) regions. Here, RE3+ (RE: Nd, Ho, Er, Tm) ions are successfully introduced into Cs4Cd1–wMnwBi2Cl12 (0 ≤ w ≤ 1) vacancy-ordered quadruple perovskites through a facile hydrothermal method. In addition to the strong orange-red Mn2+ emission, the as-prepared materials exhibit the effective characteristic emission of RE3+ in the red and NIR regions via constructing a Mn2+ energy bridge. With Mn2+ gradually replacing Cd2+ in Cs4Cd1–wMnwBi2Cl12:RE3+, the photoluminescence (PL) of RE3+ in the red and NIR ranges shows an increasing trend until it reaches the strongest value (w = 1). The energy transfer processes of [BiCl6]3– → Mn2+ → RE3+ are confirmed, and the corresponding mechanism is explored. According to the manipulation of the Mn2+/Cd2+ component, an evolution process from direct to indirect band gaps is verified via a combined experimental–theoretical approach. White light-emitting diodes (LEDs) are fabricated by employing Ho3+-doped Cs4MnBi2Cl12 on near-ultraviolet (n-UV) LED chips, achieving an improved color rendering index (CRI) from 83.3 to 93.0 compared to that of the parent compound. Codoping RE3+ (RE: Nd, Ho, Er, Tm) ions into Cs4MnBi2Cl12 results in an ultrawide emission covering both NIR I and NIR II regions, implying a great potential for NIR detection application.

Efficient ultra-broadband NIR-II emission achieved by multi-site occupancy in Mg3Ga2GeO8: Ni2+ phosphor

It is an important and urgent task to improve the luminous efficiency and emission bandwidth of existing luminescent materials with emission in near infrared (NIR) spectral region (especially for NIR-II spectral region from 1000 to 1700 nm). Herein, we report a novel Ni2+ doped phosphor Mg3Ga2GeO8: 0.8 %Ni2+ which exhibits ultra-broadband emission (from 1100 to 1700 nm, the full width at half maximum (FWHM) is up to 300 nm) with high quantum efficiency (The internal quantum efficiency (36.7 %) and external quantum efficiency (7.3 %) are relatively high in the reported Ni2+ dope NIR-II emitting phosphors). The phosphor presents desirable thermal stability of luminescence (At 373 K, it remains 56.2 % of the initial intensity at room temperature). This work not only provides an advanced NIR-II emitting phosphor which can be effectively pumped by commercial near ultraviolet light emitting diode chips, but also introduces a new strategy (that is to explore a suitable host in which there exists many different crystalline sites for the occupation of activators) for the exploration of efficient ultra-broadband NIR-II emitting phosphors.

Compact Fluorescence Detection System Based on a Monolithic DBR-Integrated III-Nitride LED Chip.

Portable applications of fluorescence detection systems have gained much attention in various fields and require system components to be small and compact. In this work, we report on a compact fluorescence detection system and demonstrate its application for fluorescence sensing and imaging. The light source and filter are integrated on a single chip for the proposed system, which not only realizes the separation between excitation and fluorescent lights but also improves the light-emitting diode (LED) light extraction efficiency. Furthermore, the detection system allows for a removable sample unit. The results indicate that the performance of the distributed Bragg reflector (DBR) filter based on an amorphous dielectric film is excellent with selection ratios larger than 4600:1. The peak emission wavelength of the LED is 528 nm. The influence of green light leakage can be neglected, and the fluorescent red light is dominant when the fluorescence detection system is used for sensing and imaging. The low-cost and monolithic DBR-integrated III-nitride LED chip makes the proposed architecture a competitive candidate for portable fluorescence detection applications.

Tailoring Dense, Orientation-Tunable, and Interleavedly Structured Carbon-Based Heat Dissipation Plates.

The controllability of the microstructure of a compressed hierarchical building block is essential for optimizing a variety of performance parameters, such as thermal management. However, owing to the strong orientation effect during compression molding, optimizing the alignment of materials perpendicular to the direction of pressure is challenging. Herein, to illustrate the effect of the ordered microstructure on heat dissipation, thermally conductive carbon-based materials are fabricated by tailoring dense, orientation-tunable, and interleaved structures. Vertically aligned carbon nanotube arrays (VACNTs) interconnected with graphene films (GF) are prepared as a 3D core-ordered material to fabricate compressed building blocks of O-VA-GF and S-VA-GF. Leveraging the densified interleaved structure offered by VACNTs, the hierarchical O-VA-GF achieves excellent through-plane (41.7W m-1 K-1 ) and in-plane (397.9W m-1 K-1 ) thermal conductivities, outperforming similar composites of S-VA-GF (through-plane: 10.3W m-1 K-1 and in-plane: 240.9W m-1 K-1 ) with horizontally collapsed carbon nanotubes. As heat dissipation plates, these orderly assembled composites yield a 144% and 44% enhancement in the cooling coefficient compared with conventional Si3 N4 for cooling high-power light-emitting diode chips.

Color integration in biomass-derived carbon dots to realize one-step white light

ABSTRACT In this work, the extract of mango leaf was chosen as a green raw material, and ethylenediamine (EDA) as a supporting material for a controllable one-step reaction to realizing white light. During the reaction, EDA could balance the precursor consumption, and participated in the formation of the carbon dots (CDs). The final integrated emitting color of the materials could be adjusted to white light with a one-step hydrothermal treatment. The composite solution was directly coated on a commercial 365 nm light-emitting diode (LED) chip without a polymer matrix and showed a stable white light with CIE coordinates of (0.326, 0.328). This work developed an interesting method for tuning the reaction process in a complex system and provided a simple way of realizing an integrated white light with a single wavelength excitation.

Pyrene-Functionalized Alkali Lignin to Disperse Hydroxylated Boron Nitride Nanosheets in Cellulose Nanofibers for Thermal Management

High-thermal-conductivity (λ) nanocomposites have been thought to resolve thermal management issues in electronic development. However, use of these is still challenging due to the easy aggregation of micro/nanofillers in a matrix. Here, a high-efficiency, low-cost, environmental strategy was developed wherein pyrene-functionalized alkali lignin (AL-PPBA) dispersants were employed to disperse hydroxylated boron nitride nanosheets (BNNS) by π–π conjugation in a cellulose nanofiber (CNF) solution, following which a nanocomposite film was prepared via the vacuum-assisted self-assembly method. Experimental and simulation results show that an efficient interfacial interaction between AL-PPBA and BNNS was achieved successfully and a stable aqueous dispersion solution was obtained. The as-prepared nanocomposites thus show λ as high as 18.27 W m–1 K–1 with the loading of 10.4 vol % of BNNS and superior anisotropy. A potential thermal management capability was demonstrated when using nanocomposites as heat sink components for light-emitting diode (LED) chips. This study provides a route to promote the dispersity of micro/nanofillers via a noncovalent cross-linking strategy and address heat management issues.

Synthesis and properties of a series of iridium complexes with naphthalenyl imidazo[2,1-b]thiazole derivatives as primary ligands

Eight iridium complexes by employing 3-methyl-6-(naphthalen-2-yl)-imidazo [2,1-b] thiazole (mn2mt) and 3-methyl-6-(naphthalene-1-yl)imidazo [2,1-b] thiazole (mn1mt) as the primary ligands, as well as picolinic acid (pic), isoquinoline-3-carboxylic acid (3-IQA), quinoline-2-carboxylic acid (2-QA), and 2-(pyridin-2-yl)phenol (hppy) as the auxiliary ligands, were synthesized for applications where organic optical function materials are required. On top of that, their structures, photoluminescence, and electrochemical properties were thoroughly investigated. More specifically, their maximum emission wavelengths can be detected in the range of 557-609 nm, while the luminous colors span from the green to the standard red region. Interestingly, by employing the synthesized IrIII complexes as emitters, light-emitting diode (LED) chips based on InGaN chip excitation were fabricated, which divulged good performances.

Toward the energy optimization of smart lighting systems through the luminous potential of photoluminescence

Lighting-related energy consumption has recently increased due to the significant expansion of buildings’ floor area and the growing demand for lighting coming from the occupants. With the aim of mitigating the global warming phenomenon by reducing the impacts of fossil fuels-powered systems, the lighting sector has faced a continuous renovation through years, up to the modern and efficient light emitting diodes (LEDs) solutions. Moving from the basic principle of phosphor-converted LEDs, consisting in the combination of phosphor materials to the radiation emitted by a LED chip, the present research investigates the response of photoluminescent pigments with different absorption and emission spectra as a function of the specific spectral distribution of the excitation source. The evolution of photoluminescence is later investigated during both the charging and the decay phase. The performance of each “pigment–lamp” pair is characterized using a spectroradiometer and a specially designed experimental equipment. Results demonstrate how a yellow-emitting material is more suitable than others for lighting purposes, providing for the highest luminance values (up to 2.61 cd/m2) and the longest decay time (>5 h). Moreover, the fastest activation of luminescence due to UV radiation (after 20–60 min of exposure) does not guarantee the most persistent and intense performance of the samples.