Phosphor-in-glass (PIG) converter sintered by a fast Joule heating process for high-power laser-driven white lighting.

Currently, laser-driven lighting based on phosphor-in-glass (PIG) has drawn much interest in solid state lighting due to its high electro-optical efficiency and high-power density. However, the fabrication of PIG requires expensive equipment, long sintering time, and high cost. In this work, we utilized a simple, fast, and high temperature Joule heating process to make phosphor-in-glass bulk sintered in less than 20 s, which greatly improved the production efficiency. The PIG converters sintered under different sintering temperatures were investigated experimentally. The optimized PIG converter exhibited high and robust luminous efficacy (164.24 lm/W), a high radiant flux, and a small CCT deviation at 3.00 W. Moreover, the optimized sample also showed high temperature resistance at 3.00 W, robust temperature management during normal working. These results indicated that the optimized PIG converter sintered by the Joule heating process could offer great potential for the application in high-power laser-driven white lighting.

Bioinspired high-scattering polymer films fabricated by polymerization-induced phase separation.

Inspired by the porous scale of the bright white beetle Cyphochilus, a polymerization-induced phase separation method is proposed to fabricate bioinspired high-scattering polymer films with porous structures. With an optimized formulation, the porous films with a mean pore size of ∼200nm feature a broadband reflectance of ∼71% at a thickness of 16 µm and are measured to have a transport mean free path of ∼3µm. The porous films with high reflectivity enable the application on light-emitting diodes and have great potential in other similar optoelectronic fields.

Numerical study on the scattering property of porous polymer structures via supercritical CO2 microcellular foaming.

Disordered porous polymer structures have gained tremendous attention due to their wide applications in various fields. As a simple yet versatile technique, supercritical CO2 microcellular foaming has been proposed to fabricate highly scattering porous polymer films, which have been used to enhance the efficiency of quantum dots (QDs) films. In the foaming process, numerous enclosed pores are generated, which induce significant scattering, underpinning the efficiency enhancement in optoelectronic devices. However, the scattering property of foamed porous structures has still not been well investigated, and effective guidelines for engineering the porous structures are still not available. In this work, we use Mie scattering theory and ray-tracing simulation to analyze the optical property of a single pore, pore assembly, and porous film. Furthermore, it is demonstrated that the scattering scheme in the porous QD films leads to a large enhancement of excitation light absorption and QD emission extraction. It is envisioned that our work will contribute to the engineering guidelines of porous structures and boost the application of porous structures in similar fields.

Microlens arrays with adjustable aspect ratio fabricated by electrowetting and their application to correlated color temperature tunable light-emitting diodes.

We develop a facile, fast, and cost-effective method based on the electrowetting effect to fabricate concave microlens arrays (MLA) with a tunable height-to-radius ratio, namely aspect ratio (AR). The electric parameters including voltage and frequency are demonstrated to play an important role in the MLA forming process. With the optimized frequency of 5 Hz, the AR of MLA are tuned from 0.057 to 0.693 for an increasing voltage from 0 V to 180 V. The optical properties of the MLA, including their transmittance and light diffusion capability, are investigated by spectroscopic measurements and ray-tracing simulations. We show that the overall transmittance can be maintained above around 90% over the whole visible range, and that an AR exceeding 0.366 is required to sufficiently broaden the transmitted light angular distribution. These properties enable to apply the developed MLA films to correlated-color-temperature (CCT)-tunable light-emitting-diodes (LEDs) to enhance their angular color uniformity (ACU). Our results show that the ACU of CCT-tunable LEDs is significantly improved while preserving almost the same lumen output, and that the MLA with the highest AR exhibits the best ACU performance.

Investigation of stability and optical performance of quantum-dot-based LEDs with methyl-terminated-PDMS-based liquid-type packaging structure.

Although quantum dots (QDs) have a high quantum yield close to one in a solution, they exhibit low conversion efficiency in a solidification polymer matrix, which hampers the development of QD-based light-emitting diodes (LEDs) with high stability and optical performance. In this study, we proposed a methyl-terminated-polydimethylsiloxane-(PDMS)-based liquid-type packaging structure (LPS) to improve stability and optical performance of QD-based LEDs. Compared with the traditional ethylene-terminated-PDMS-based solid-type packaging structure, the LPS with an optimized kinematic viscosity of 10000 m2/s can provide higher stability and optical performances for QD-based LEDs, including total radiant power and luminous flux. Consequently, the proposed effective and simple strategy has great potential for illumination and display applications.

Investigating the transformation of CsPbBr3 nanocrystals into highly stable CsPbBr3/Cs4PbBr6 nanocrystals using ethyl acetate in a microchannel reactor.

The nanocrystals (NCs) of inorganic perovskites CsPbX3 and Cs4PbX6 (X = Cl, Br, I) are showing a great development potential due to their versatility of crystal structure. Here, we used a microchannel reactor to synthesize both CsPbBr3 NCs (CsPbBr3 NCs) and Cs4PbBr6 NCs with embedded CsPbBr3 (CsPbBr3/Cs4PbBr6 NCs). Via speed control of the precursor, ligands around the surface of NCs were effectively regulated by ethyl acetate, allowing the transformation from CsPbBr3 NCs to CsPbBr3/Cs4PbBr6 NCs in a short time, an outstanding stability of NCs, and a better crosslinking between NCs and polymer for the application of LEDs. Without any protection, the CsPbBr3/Cs4PbBr6 NCs, with a production rate of 28 mg min-1, retain more than 90% of the PL intensity after 84 d. Finally, the CsPbBr3/Cs4PbBr6 NCs were used to produce an LED device, and a wide color gamut of 122.8% NTSC or 91.7% Rec 2020 was attained.

Improving the optical performance of multi-chip LEDs by using patterned phosphor configurations.

In order to improve the color uniformity of multi-chip LEDs, a patterned phosphor configuration has been proposed by using pulsing spray process. The patterned phosphor has detached yellow and red phosphor regions matching every single LED chip. Optical performances of different phosphor parameters are experimentally investigated. The results show that the yellow central coating (YCC) configuration produces outstanding performance not only in chromatic uniformity but also in luminous. In comparison with the conventional phosphor coating, the YCC patterned phosphor LED can improve the luminous flux by 20.6%, and decrease the difference of the correlated color temperature (CCT) distribution from 1362K to 489K. We believe that the patterned phosphor configuration can be used for improving optical properties of multi-chip LEDs.

Effect of flip-chip height on the optical performance of conformal white-light-emitting diodes.

To improve the optical performance of the conformal white light-emitting diodes (LEDs), previous studies mainly focus on the phosphor structures design by simulations and experiments methods. However, one of the most critical parameters, i.e., the height of chips, is barely studied. In this study, we have experimentally investigated the effect of the flip-chip height on the optical performance of conformal white LEDs. The results show that larger chip height can cause lower radiant power and luminous flux, while wider viewing angles can be achieved. By selecting a suitable chip height of 200 µm, superior color uniformity for white LEDs can be obtained with only 168 K correlated color temperature (ΔCCT). This study can provide a new perspective to improve the color uniformity without changing the phosphor structures or using special scattering elements; moreover, it can facilitate the selection of a proper chip height, considering different illumination requirements. Further investigations on the chip height considering packaging structures are still necessary to improve the luminous flux and the color uniformity simultaneously.

Full spectral optical modeling of quantum-dot-converted elements for light-emitting diodes considering reabsorption and reemission effect.

Quantum dots (QDs) have attracted significant attention in light-emitting diode (LED) illumination and display applications, owing to their high quantum yield and unique spectral properties. However, an effective optical model of quantum-dot-converted elements (QDCEs) for (LEDs) that entirely considers the reabsorption and reemission effect is lacking. This suppresses the design of QDCE structures and further investigation of light-extraction/conversion mechanisms in QDCEs. In this paper, we proposed a full spectral optical modeling method for QDCEs packaged in LEDs, entirely considering the reabsorption and reemission effect, and its results are compared with traditional models without reabsorption or reemission. The comparisons indicate that the QDCE absorption loss of QD emission light is a major factor decreasing the radiant efficacy of LEDs, which should be considered when designing QDCE structures. According to the measurements of fabricated LEDs, only calculation results that entirely consider reabsorption and reemission show good agreement with experimental radiant efficacy, spectra, and peak wavelength at the same down-conversion efficiency. Consequently, it is highly expected that QDCE will be modeled considering the reabsorption and reemission events. This study provides a simple and effective modeling method for QDCEs, which shows great potential for their structure designs and fundamental investigations.

Effect of ZnO nanostructures on the optical properties of white light-emitting diodes.

White light produced by blue LEDs with yellow phosphor is the most widely used methods, but it results in poor quality in angular CCT uniformity. In this work, a novel technique was introduced to solve this problem by integrating different ZnO nanostructures into white light-emitting diodes. The experiment of ZnO doped films and the simulation of Finite-Difference Time-Domain (FDTD) were carried out. The result indicated scattering effect of ZnO nanoparticles could improve uniformity of scattering energy effectively. Moreover, the effect of ZnO nanostructures on white light-emitting diodes (wLEDs) devices was also investigated. The CCT deviation of wLEDs devices would decrease from 3455.49 K to 96.30 K, 40.03 K and 60.09 K when the node-like (N-ZnO), sheet-like (S-ZnO) and rod-like ZnO (R-ZnO) respectively applied. The higher CCT uniformity and little luminous flux dropping were achieved when the optimal concentrations of N-ZnO, S-ZnO, and R-ZnO nanostructures were 0.25%, 0.75%, and 0.25%. This low-cost and green manufacturing method has a great impact on development of white light-emitting diodes.

CCT-tunable LED device with excellent ACU by using micro-structure array film.

We apply a microstructure array (MSA) film to improve the angular color uniformity (ACU) of a correlated-color-temperature-tunable LED (CCT-tunable LED) with tunable CCT ranging from 2700 to 6500 K. The effects of the MSA film area and the height between the film and LED are investigated and optimized. The resulting ACU is greatly improved for all CCT ranges with little luminous flux loss. For a typical CCT range of 3000-4000 K, with a full-covering MSA film and height H = 5 mm, the CCT deviation is significantly reduced from 1090 K to 218 K, with only 1.8% luminous flux loss.

Color uniformity enhancement for COB WLEDs using a remote phosphor film with two freeform surfaces.

The color uniformity (CU) of chip-on-board (COB) white light emitting diodes (WLEDs) has been improved by using remote phosphor films with two freeform surfaces (TFS-RPFs). The finite-difference time-domain (FDTD), Monte Carlo ray-tracing, and color-thickness feedback (CTFB) methods were used to design the TFS-RPFs: the blue light distribution of COB WLEDs is greatly affected by the angular thickness distribution of TFS-RPFs, and a high CU can be achieved iteratively. The directional inconsistency of incident and emergent blue light, scattering effect of TFS-RPFs, and illumination characteristics of the COB source were also investigated. COB WLEDs containing optimized TFS-RPFs achieved high CU with a decrease of 26.2% in maximum CCT deviation; thus, TFS-RPFs can improve the CU of COB WLEDs.

Energy feedback freeform lenses for uniform illumination of extended light source LEDs.

Using freeform lenses to construct uniform illumination systems is important in light-emitting diode (LED) devices. In this paper, the energy feedback design is used for freeform lens (EFFL) constructions by solving a set of partial differential equations that describe the mapping relationships between the source and the illumination pattern. The simulation results show that the method can overcome the illumination deviation caused by the extended light source (ELS) problem. Furthermore, a uniformity of 95.6% is obtained for chip-on-board (COB) compact LED devices. As such, prototype LEDs manufactured with the proposed freeform lenses demonstrate significant improvements in luminous efficiency and emission uniformity.

Improving LED CCT uniformity using micropatterned films optimized by combining ray tracing and FDTD methods.

Although the light-emitting diode (LED) has revolutionized lighting, the non-uniformity of its correlated color temperature (CCT) still remains a major concern. In this context, to improve the light distribution performance of remote phosphor LED lamps, we employ a micropatterned array (MPA) optical film fabricated using a low-cost molding process. The parameters of the MPA, including different installation configurations, positioning, and diameters, are optimized by combining the finite-difference time-domain and ray-tracing methods. Results show that the sample with the upward-facing convex-cone MPA film that has a diameter of half of that of the remote phosphor glass, and is tightly affixed to the inward surface of the remote phosphor glass renders a superior light distribution performance. When compared with the case in which no MPA film is used, the deviation of the CCT distribution decreases from 1033 K to 223 K, and the corresponding output power of the sample is an acceptable level of 85.6%. We perform experiments to verify our simulation results, and the two sets of results exhibit a close agreement. We believe that our approach can be used to optimize MPA films for various lighting applications.

Carbon carrier-based rapid Joule heating technology: a review on the preparation and applications of functional nanomaterials.

Compared to conventional heating techniques, the carbon carrier-based rapid Joule heating (CJH) method is a new class of technologies that offer significantly higher heating rates and ultra-high temperatures. Over the past few decades, CJH technology has spawned several techniques with similar principles for different application scenarios, including ultra-fast high temperature sintering (UHS), carbon thermal shock (CTS), and flash Joule heating (FJH), which have been widely used in material preparation research studies. Functional nanomaterials are a popular direction of research today, mainly including nanometallic materials, nanosilica materials, nanoceramic materials and nanocarbon materials. These materials exhibit unique physical, chemical, and biological properties, including a high specific surface area, strength, thermal stability, and biocompatibility, making them ideal for diverse applications across various fields. The CJH method is a remarkable approach to producing functional nanomaterials that has attracted attention for its significant advantages. This paper aims to delve into the fundamental principles of CJH and elucidate the efficient preparation of functional nanomaterials with superior properties using this technique. The paper is organized into three sections, each dedicated to introducing the process and characteristics of CJH technology for the preparation of three distinct material types: carbon-based nanomaterials, inorganic non-metallic materials, and metallic materials. We discuss the distinctions and merits of the CJH method compared to alternative techniques in the preparation of these materials, along with a thorough examination of their properties. Furthermore, the potential applications of these materials are highlighted. In conclusion, this paper concludes with a discussion on the future research trends and development prospects of CJH technology.

Editorial for the Special Issue "Microsystem for Electronic Devices".

The field of microsystems is a rapidly evolving area with a wide range of applications in the field of electronics [...].

Perovskite-Gallium Nitride Tandem Light-Emitting Diodes with Improved Luminance and Color Tunability.

Tandem structures with different subpixels are promising for perovskite-based multicolor electroluminescence (EL) devices in ultra-high-resolution full-color displays; however, realizing excellent luminance- and color-independent tunability considering the low brightness and stability of blue perovskite light-emitting diodes (PeLEDs) remains a challenge. Herein, a bright and stable blue gallium nitride (GaN) LED is utilized for vertical integration with a green MAPbBr3 PeLED, successfully achieving a Pe-GaN tandem LED with independently tunable luminance and color. The electronic and photonic co-excitation (EPCE) effect is found to suppress the radiative recombination and current injection of PeLEDs, leading to degraded luminance and current efficiency under direct current modulation. Accordingly, the pulse-width modulation is introduced to the tandem device with a negligible EPCE effect, and the average hybrid current efficiency is significantly improved by 139.5%, finally achieving a record tunable luminance (average tuning range of 16631 cd m-2 at an arbitrary color from blue to green) for perovskite-based multi-color LEDs. The reported excellent independent tunability can be the starting point for perovskite-based multicolor EL devices, enabling the combination with matured semiconductor technologies to facilitate their commercialization in advanced display applications with ultra-high resolution.

A Luminous Efficiency-Enhanced Laser Lighting Device with a Micro-Angle Tunable Filter to Recycle Unconverted Blue Laser Rays.

In this work, a phosphor converter with small thickness and low concentration, based on a micro-angle tunable tilted filter (ATFPC), was proposed for hybrid-type laser lighting devices to solve the problem of silicone phosphor converters' carbonizing under high-energy density. Taking advantage of the filter and the scattering characteristics of microphosphors, two luminous areas are generated on the converter. Compared with conventional phosphor converters (CPCs), the lighting effects of ATFPCs are adjustable using tilt angles. When the tilt angle of the micro filter is 20°, the luminous flux of the ATPFCs is increased by 11.5% at the same concentration; the maximum temperature (MT) of ATFPCs is reduced by 22.8% under the same luminous flux and the same correlated color temperature (CCT) 6500 K. This new type of lighting device provides an alternative way to improve the luminous flux and heat dissipation of laser lighting.

Research on Laser Illumination Based on Phosphor in Metal (PiM) by Utilizing the Boron Nitride-Coated Copper Foams.

Laser-driven illumination has unique advantages in high-power applications. Taking advantage of the valuable experience of light-emitting diodes (LED) development, phosphor in silicone (PiS) is considered to be one of the most potential commercial phosphor converter solutions for laser-driven illumination. However, the thermal quenching of the PiS converter is a bottleneck problem. Herein, a boron nitride (BN)-coated copper foam strategy is introduced for the laser-driven illumination system. The phosphor/silicone is embedded in the designed BN/copper foam to form a phosphor in metal (PiM) converter. Copper foam serves as an internal connected heat transfer channel; the BN coating solves the light absorption problem of the copper foam effectively. Based on this PiM(BN/copper foam) design, the heat dissipation is effectively improved. Under high-power laser excitation (8.13 W), the PiS converter cannot reach thermal equilibrium, and therefore the temperature increases sharply up to 660 °C. In comparison, the thermal performance of an optimized PiM(BN/copper foam) converter is able to maintain excellent stability, where the maximum temperature is only 166.5 °C. The proposed PiM strategy has a maximum temperature that is 493.5 °C lower than that of the reference PiS solution. Due to the superior thermal management, the luminous efficiency of the illumination system is constantly stable at 254 lm/W, though with less phosphor mass; and the related color temperature is about 6000 K all the time. This provides a practical and feasible heat-dissipation solution for high-power laser-driven illumination.

Toward 200 Lumens per Watt of Quantum-Dot White-Light-Emitting Diodes by Reducing Reabsorption Loss.

In this study, we analyze the influence of the pore structure of an SBA-15 particle on the light emission from its inner adsorbed quantum dots (QDs) and outer light-emitting diode (LED) chips. It is found that the particle features of a high refractive index, comparable feature size of pore structure, and lower amount of QD adsorption help with QD light extraction, demonstrating a mechanism to suppress QD light propagating through pores and thus reducing the reabsorption loss. We consequently developed highly efficient QD white LEDs with wet-mixing QD/SBA-15 nanocomposite particles (NPs) by further optimizing the packaging methods and the introduced NP mass ratio. The LEDs demonstrated a record luminous efficacy (the ratio of luminous flux to electrical power) of 206.8 (entrusted test efficiency of 205.8 lm W-1 certificated by China National Accreditation Service) and 137.6 lm W-1 at 20 mA for white LEDs integrating only green QDs and green-red QD color convertors, respectively, with improved operating stability. These results are comparable to conventional phosphor-based white LEDs, which can be a starting point for white LEDs only using QDs as convertors toward commercialization in the near future.