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Quantum dots (QDs) are ideal color-conversion materials for display fields. Preparation of micro-nanostructures is a mainstream method for obtaining a high photoluminescence (PL) intensity. Electrical induction, a method of preparing micro-nanostructures, was introduced to obtain QD films with high PL performance by preparing a sandwich column array structure (SCAS). By changing the spacer thickness, a series of SCAS-QD films were fabricated, after optimizing the voltage. The SCAS-QD layers with a 25- $\mu \text{m}$ spacer obtained the maximum PL enhancement of green light intensity: up to 42.8%. The enhancement was caused by the microcavity trapping and light extraction effects. The former could increase the utilization factor of blue light and the latter could increase the emission probability of green light. This is a simple, high-efficient, and low-cost method for preparing QD films with high PL performance without increasing the QD concentration.

The correlated color temperature (CCT) variation of the phosphor-converted light-emitting diodes (LEDs) after curing is a common phenomenon. In the past, it was believed that the phenomenon was caused by the sedimentation of phosphor particles. However, not only sedimentation, but these particles can also flow with the natural convection of silicone because of nonuniform heating during curing. The convective flow of the phosphor particles during curing was studied in detail in this work. The CCT variation and phosphor particles flow in the LED device cup with different depths and wall inclination angles were studied. The results show that the CCT increases after curing when the depth of the device cup is shallow. The case is the opposite when the depth of the device cup is deep. The convective flow behaviors of the silicone were revealed in the simulation. The large-angle inclined wall can increase the silicone flow path length and inhibit the particles flow downward caused by the flow to a certain extent. It is envisioned that the findings will strengthen the understanding of the CCT variation phenomenon and guide the encapsulation structure design of LEDs for better color quality.

Self-accelerating beams have the unusual ability to remain diffraction-free while undergo the transverse shift during the free-space propagation. We theoretically identify that the transverse optical field distribution of 2D self-accelerating beam is determined by the selection of the transverse Cartesian coordinates, when the caustic method is utilized for its trajectory design. Based on the coordinate-rotation method, we experimentally demonstrate a scheme to flexibly manipulate the rotation of transverse optical field for 2D self-accelerating beams under the condition of a designated trajectory. With this scheme, the transverse optical field can be rotated within a range of 90 degrees, especially when the trajectory of 2D self-accelerating beams needs to be maintained for free-space photonic interconnection.

Visible light communication (VLC) is considered as a significant technology for new-generation communication. The VLC is supposed to provide high data rates and steady network links, which has high potential in dynamic wireless network transmission such as vehicle-to-vehicle communication. However, V2V network is always dynamic, which needs the receiver of the VLC system to have a large field of view (FOV) for stable networking. In this article, we proposed a sandwich structure light-trapping fluorescence antenna (LTFA). The LTFA consists of a short-wavelength pass long-wavelength reflect (SPLR) filter, a reflected mirror, and a 625-nm CdSe/ZnS quantum dots (QDs) fluorescent layer sandwiched between them. Multiple sets of variables of LTFA have been studied for optimization. A V2V VLC (V2V-VLC) system was built based on a commercial laser headlight. The FOV performance showed that a receiver with LTFA provides an incredible increment on receiving FOV, from 30° to 80°, while remaining considerable receiving signal power with an average optical gain of 1.6 for 80° FOV and an average optical gain of 10.45 for outer FOV. With the proposed LTFA, the average signal-to-noise ratio (SNR) of the V2V-VLC system can be improved 49% at 0°–80° and 123% at 30°–80°, respectively, showing promising communication performance.

Perovskite light emitting diodes (PeLEDs) have attracted considerable research attention because of their external quantum efficiency (EQE) of >20% and have potential scope for further improvement. However, compared to red and green PeLEDs, blue PeLEDs have not been extensively investigated, which limits their commercial applications in the fields of luminance and full-color displays. In this review, blue-PeLED-related research is categorized by the composition of perovskite. The main challenges and corresponding optimization strategies for perovskite films are summarized. Next, the novel strategies for the design of device structures of blue PeLEDs are reviewed from the perspective of transport layers and interfacial layers. Accordingly, future directions for blue PeLEDs are discussed. This review can be a guideline for optimizing perovskite film and device structure of blue PeLEDs, thereby enhancing their development and application scope.

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.

Parking problems caused by a lack of parking spaces have exacerbated traffic congestion and worsened environmental pollution. An analysis of the cruising process for parking can provide new perspectives to reduce cruising. Based on a parking survey conducted in Beijing, the authors collected a large amount of trajectory data of cruising vehicles. Then, fluctuation indexes of trajectories were proposed to analyse travellers’ cruising processes for parking. The spectral clustering method based on a hidden Markov model (HMM) was used to recognise the cruising trajectories. The recognition performance for three-dimensional trajectory data is better. Cruising trajectories for Clusters 1, 2, 3, 4, and 6 have large fluctuations and a weightier effect on road traffic. These groups can be taken as target groups for intelligent parking guidance and recommendations. The recognition accuracies for parking location and parking status increase with increasing intercepted trajectory lengths. 150 m from far to near the desired destination can be used as a threshold of the cruising trajectory length to accurately predict travellers’ parking location and status. These research results can be applied in intelligent parking systems to dynamically predict parking situations, formulate parking guidance schemes and information release strategies, and improve parking efficiency.

Vertical-cavity surface-emitting laser (VCSEL) devices operate using a variety of viewing angles to satisfy the demands of different applications. One simple and universal approach to accomplish this is by using scattering elements in the packaging process for VCSEL chips. However, inevitable backward scattering loss is introduced, which suppresses the radiant efficacy of VCSEL devices. Therefore, we have proposed an enhanced specular reflection (ESR) structure with an opening circle window (OCW) to recycle the backward scattered light. The ray-tracing method is used to optimize the diameter of the OCW, as well as the thickness of the ESR structure. Furthermore, the light extraction mechanism is discussed. According to theoretical results, VCSEL devices with optimized ESR structures are fabricated and compared with traditional VCSEL devices. The experiment results demonstrate that ESR structures can significantly enhance the radiant efficacy of VCSEL devices using scattering elements. This shows great potential for applications involving illumination and 3-D imaging.

Quantum-dot (QD) white light-emitting diodes (LEDs) are promising for illumination and display applications due to their excellent color quality. Although they have a high quantum yield close to unity, the reabsorption of QD light leads to high conversion loss, significantly reducing the luminous efficacy and stability of QD white LEDs. In this report, SBA-15 mesoporous particles (MPs) with two-dimensional hexagonal pore structures (2D-HPS) are utilized to largely enhance the luminous efficacy and color-conversion efficiency of QD white LEDs in excess of 50%. The reduction in conversion loss also helps QD white LEDs to achieve a lifetime 1.9 times longer than that of LEDs using QD-only composites at harsh aging conditions. Simulation and testing results suggest that the waveguide effect of 2D-HPS helps in reducing the reabsorption loss by constraining the QD light inside the wall of 2D-HPS, decreasing the probability of being captured by QDs inside the hole of 2D-HPS. As such, materials and mechanisms like SBA-15 MPs with 2D-HPS could provide a new path to improve the photon management of QD light, comprehensively enhancing the performances of QD white LEDs.

Quantum dots (QDs) attract great attention due to their narrow emission spectra, providing excellent light quality for light-emitting diodes (LEDs) in illumination and display applications. However, their low thermal reliability suppresses the commercial applications of QD-based LEDs. In this report, it is the first time that we realize high thermal performance and reliability QD-based LEDs with watt-level injection power. The QD-on-reflector (QOR) structure is proposed to separate QDs from the heat source of chips, and targeted cooling for QD/polymer composites is achieved with an Al-based reflector. Compared with the reference [conventional QD-on-chip (QOC) structures], the QOR-LEDs exhibit higher total radiant power/luminous flux and color consistency. Most important, the QOR-LED has a steady temperature of only approximately 50 °C in QD/polymer composites, which is 90 °C lower than the reference and is the reported lowest temperature for QD-based LEDs. The working-aging test shows that the luminous flux maintenance (LFM) factor of the QOR-LED is 92.2%, whereas that of the reference is only 21.2% after aging for 20 min. This corresponds to a lifetime of 88.5 times longer than that of the QOC-LED at the same LFM of 20%. Consequently, the QOR structure can provide better optical performance, superior thermal performance, and longer lifetime for QD-based LEDs.

The inorganic halide perovskite quantum dots (QDs) have been considered as a promising substitute for white light-emitting diodes (WLEDs). In this paper, the green CsPbBr3 QDs and red K2SiF6:Mn4+ (KSF) phosphor were used to fabricate the conversion layers. Because the location of the layers is fundamental to the absorption priority of blue light, the location of KSF and QDs were controlled and the QDs-up type and QDs-down type WLEDs were made. The optical power, luminous efficiency, CCE, and luminous intensity in the middle of QDs-up type are 13.83 mW, 13.54 lm/W, 11.94%, and 2.65 cd, meaning 24.26%, 25.72%, 2.63%, and 23.83% higher than those of QDs-down type, respectively. In addition, the QDs-up type has a lower correlated color temperature (CCT) shift of 734 K and a decreased highest temperature of 56.8° (51.5% and 14.9% lower). These key property differences indicate that the QDs-up type is more suitable for the application in display and backlight. In order to explore the reasons for these differences, the emission spectra, CCE, reflection rate, absorption rate, and temperature curves of QDs or KSF films were also analyzed, which provided a better understanding of designing package structures.

Perovskite quantum dots (QDs) attracted a lot of attention recently due to their high light conversion efficiency, and high color purity. However, perovskite materials are sensitive to heat. High temperature will cause serious quenching problem of the perovskite QDs. In order to solve the QDs thermal quenching problem without destroying their optical characters. A circulating quantum dots colloidal solution converter (CQD-converter) was developed. A closed loop pump tube coated with Teflon was utilized to prevent perovskite QDs from the external environment. A peristaltic pump was utilized to drive the QDs colloidal solution through a Peltier cooler for dissipating the heat of the QDs colloidal solution. The lifetime of the perovskite QDs can be significantly improved under a 450nm laser excitation. The effects of temperature of the Peltier cooler and flow velocity on the optical properties of QDs were also investigated. Compared to the static quantum dots colloidal solution (SQD-converter), which quenched after 7 min, the optical properties were maintained after 600 min for the CQD-converter.

Micro-scale patterned arrays and nano-scale rough morphology are promising for improving the light-extraction performance of GaN-based thin film light-emitting diodes (TFLEDs), while the light-extraction mechanisms of the multiscale architectures combining these two structures have not been investigated yet. In this report, we have adopted a pattern transfer and wet etching combined method to fabricate multiscale patterned arrays with rough morphology (msPARM) on n-GaN layers for TFLEDs and investigated their light-extraction mechanisms by the finite-difference time domain and ray-tracing combined method. The results show that the TFLEDs achieve the maximum radiant efficacy using the msPARM with an etching time of 8 min, which is increased by 16.3% and 1.7% compared with that achieved using only the patterned arrays or only the rough morphology, respectively. Most importantly, optical simulation reveals that the msPARM can provide a high transmittance for light with large emission angles from the active region using the inclined surface of micro-scale concave cones, while effectively suppressing the reflection loss for light with small emission angles using the scattering effect of nano-scale rough morphology, resulting in enhancing the light-extraction of the TFLEDs. Consequently, this study can provide a better understanding to design the multiscale structures for achieving high efficiency LEDs.

Thermal management of electronic equipment has been a key factor in the development of electronic devices. The fin heat sink is one of the most common types of heat dissipation in the industry. However, the shape of the cooling fins used in conventional straight fin heat sinks is usually fixed. The impurities such as dust and fibers in the air are likely to accumulate at the roots and edges of the cooling fins, blocking the heat dissipation path and reducing the heat dissipation efficiency. In this work, by coupling with Shape Memory Alloy (SMA), we propose a temperature self-adapting (TSA) heat sink, which has self-adapting fins to open and close as temperature changes. Compared with traditional fixed fin heat sink, this TSA heat sink can better adapt to the varying working conditions of electronic devices at different temperatures. The thermal performance and dustproof capability of the TSA heat sink were analyzed. As for a unit TSA heat sink, the cooling rate of the substrate can adjust itself as the heat source temperature increases. Under fouling conditions with American Society of Heating, Refrigerating and Air-Conditioning Engineers Standard Dust (ASHRAE Standard Dust), when the fouling was in the limit situation (full-filled), the substrate temperature of the conventional heat sink was 21.83% higher than that of the TSA heat sink, indicating that the TSA heat sink can play a better role in dustproof performance. This TSA heat sink provides a new adaptive structure of heat dissipation, which is conducive to the development of electronic devices.

Near-ultraviolet light-emitting diodes (NUV- LEDs) are more likely to be commercial due to its mature chip fabrication process and package technologies. However, the low light extraction efficiency (LEE) of NUV-LEDs limits its commercialization. In this study, we introduce a novel pre- prepared lens packaging structure for NUV-LEDs incorporating with scattering particles and optimize their structures by the optical simulation methods. Three packaging types structure including the blank LED, LED incorporating with scattering particles, and LED incorporating with scattering particles and pre-prepared lens are modeled for optical simulation. The influence of different scattering condition, lens structure and the substrate reflectivity were studied in detail by comparing different packaging types of NUV-LEDs. The light output power is extracted for comparisons after simulation. The NUV-LEDs with lens structure perform the best in light output power, and the improvement keeps rising with the higher bulk scattering coefficient. Besides, the reflectivity of the substrate contributes greatly to the component light extraction. Furthermore, the lens structure with different diameters were optimized and the result shows that the larger diameter lens can obtain greater improvement in optical output. When the reflectivity of the LED substrate is set as 80%, the NUV-LED with silicone and particles mixtures as well as lens structure shows 14.27% improvement in optical output power compared with the NUV-LED with particles and silicone mixtures at the bulk scattering coefficient value of 1 mm-1. Consequently, the novel pre-prepared lens packaging structure could greatly improve the optical output of NUV-LEDs.

The correlated color temperature (CCT) shift after the polymer curing process is a very common phenomenon in Light Emitting Diodes (LEDs) packaging. During the curing process, the particles in LED encapsulant will flow with the fluid due to the nonuniform heating inside the polymer. Then, the polymer and the phosphor particles will solidify very quickly when the cross-linking reaction is trigged. In order to investigate the difference of the phosphor positions before and after the curing, in this work, a finite element analysis (FEA) simulation was carried out to simulate the flow of the polymer that contained the phosphors. The light color performance was subsequently simulated by finite-difference time-domain (FDTD) and Ray tracing (RT) combined method. As the result shows, the flow of LED encapsulant with phosphor particles can change the concentration of phosphor in different layers of LED encapsulant. Such changes can cause redshift and blueshift of transmitted light. Finally, new structure encapsulation cups were proposed to inhibit the flow of LED encapsulant with phosphor particles. The results shows that the serrated encapsulation cup can effectively inhibit the change of concentration during LED encapsulant curing.

Phosphor-converted light-emitting diode (pcLED) is one of the most promising methods to generate white light. The interaction of the excitation light with the phosphor in pcLED is a complicated phenomenon, combining light absorption, light conversion, and scattering. An effective and efficient way to predict the optical behavior of pcLED is using the bidirectional scattering distribution function (BSDF). In this paper, the BSDF for pcLEDs with arbitrary phosphor concentration and thickness was established. The measured integrating energy and angular distributions of BSDF were successfully fitted by the interpolation method and the ABg model, respectively, realizing the calculation of BSDF values for arbitrary phosphor configurations. The proposed model was applied to a remote pcLED using an arbitrary phosphor configuration in Monte Carlo simulation. The output radiant power and the angular distributions of the blue and yellow light show good agreements between experiments and simulations; the errors of radiant power were all less than 4%, validating the effectiveness of the model. Consequently, this study provides a simple and useful tool to precisely predict the optical performance of pcLEDs with arbitrary concentration and thickness, it is essential for white LED design and fabrication.

Quantum dots (QDs) show a great potential for light-emitting diodes (LEDs) packaging, which still face great challenges compared with the matured phosphor downconversion materials. These are probably caused by the unique scattering and absorption properties of QDs, which are extremely different to the traditional phosphor due to their several nanometers size, while their effect on QDs-converted LEDs (QCLEDs) is barely studied. In this paper, we have experimentally and theoretically investigated the effect of scattering and absorption of CdSe/ZnS QDs on the optical performance for QCLEDs by comparing with the traditional yttrium aluminum garnet phosphor. Results indicate that the strong absorption (reabsorption) of QDs causes low radiant efficacy and stability for QCLEDs; their weak scattering also leads to a low color uniformity. It demonstrates that their unique scattering and absorption properties are key factors leading to low optical performance of QCLEDs compared with the traditional phosphor-converted LEDs. For purpose of gaining the white LED with high efficiency and stability, it is highly suggested to use a low QD concentration to reduce the reabsorption loss and the total internal reflection loss. We believe that this paper can provide a better understanding of improving the optical performance for QCLEDs from the prospective of scattering and absorption. In the future, it is important to use low QD concentration to gain high-performance white LEDs with high downconversion efficiency by optimizing packaging structures.

Chip-scaled package light-emitting diodes (CSP LEDs) are promising for illumination applications because of their advantages of compact size and high luminous density. Contrary to traditional conformal package structures, the material and thickness of top and sides, respectively, are controllable, showing great potential to achieve high color uniformity. In this letter, different kinds of CSP LEDs were comprehensively compared, and the requirements to gain high color uniformity were further investigated with simulation and experiment. Results show that a top volume proportion of phosphor ${V}_{\mathrm {top}}$ between 75% and 85% contributes to high color uniformity for the universally used 35 and 45 mil flip chips. The fabricated CSP LEDs with $V_{\mathrm {top}}=77.8\% $ can gain an extra uniform color distribution with a $\Delta $ CCT of only 92 K at a CCT of approximately 6000 K, which is 82.1% lower than that of traditional conformal LEDs. These results indicate that the CSP structure is an important alternative for illumination applications requiring high color uniformity.

A rapid synthetic method for highly photoluminescent (PL) nitrogen-doped carbon quantum dots (N-CQDs) was developed by using a microreactor with foamy copper having different porosities. By taking advantage of the foamy copper, we obtained a high quantum yield (QY) of 84.1%, which was more efficient than most of the previous reports. Compared to the procedure without adding foamy copper, the QY when foamy copper was used was two times higher. The formation mechanism of the N-CQDs, which involved molecular condensation and the formation of carbon cores, was demonstrated. To explore the relationship between the use of a microreactor with foamy copper having different porosities and the PL properties of the N-CQDs, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis was employed. The results show that the surface functional groups and elemental contents influence the PL emission. We further demonstrate the application of the N-CQDs as probes for heavy metal ion detection. The results indicated that N-CQDs are very suitable for use as nanoprobes for Hg2+ ion detection and that the lowest detection limit (LOD) for Hg2+ is 2.104 nM, which is superior to many other research studies. This method highlights that the value of microreactor synthetic system as a tool for the environmental and hazard detection.

We demonstrate an organic macromolecule-assisted anion-exchange reaction method for tuning the emission spectrum of cesium lead halide perovskite (CsPbX3) nanocrystals (NCs) from green to near-ultraviolet using a microreactor. Using poly(lactic acid) (PLA), the emission peak of CsPbX3 NCs can be tuned from 514 nm to 420 nm while maintaining high photoluminescence (PL) quantum yields (QYs) of 33–90%. By taking advantage of the microreactor, we synthesize parent CsPbBr3 NCs and complete anion-exchange reactions at the same time, which is more efficient than most previously reported methods. The stability of CsPbX3 NCs is improved by PLA coating, especially for CsPbCl3, which shows long-term stability under ambient conditions for at least two weeks. The CsPbBr3 NCs are utilized with a red phosphor on a blue light emitting-diode (LED) chip, achieving white light emission with a luminous efficacy of 62.93 lm W−1 under a 20 mA driving current. Highly efficient white LEDs (wLEDs) demonstrate the potential of halide perovskite NCs for optoelectronic applications, including low-cost displays, lighting, and optical communication.

Rapidly obtaining strong photoluminescence (PL) of carbon dots with high stability is crucial in all practical applications of carbon dots, such as cell imaging and biological detection. In this study, we proposed a rapid, continuous carbon dots synthesis technique by using a microreactor method. By taking advantage of the microreactor, we were able to rapidly synthesized CDs at a large scale in less than 5 min, and a high quantum yield of 60.1% was achieved. This method is faster and more efficient than most of the previously reported methods. To explore the relationship between the microreactor structure and CDs PL properties, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were carried out. The results show the surface functional groups and element contents influence the PL emission. Subsequent ion detection experiments indicated that CDs are very suitable for use as nanoprobes for Fe 3 + ion detection, and the lowest detection limit for Fe 3 + is 0.239 μM, which is superior to many other research studies. This rapid and simple synthesis method will not only aid the development of the quantum dots industrialization but also provide a powerful and portable tool for the rapid and continuous online synthesis of quantum dots supporting their application in cell imaging and safety detection.

The inverted dispensing (ID) method is proposed to fabricate remote phosphor layers (RPLs) with cone-like shapes for white light-emitting diodes (WLEDs) to improve their color uniformity. We introduce surface evolver packages and optical simulations to study the effect of the surface tension on the optical performance of these WLEDs during the ID process. The results show that a decreasing surface tension contributes to a sharpened geometry of the RPL. This sharpened surface geometry is responsible for the optimization of the color uniformity by deflecting blue light towards central angles. The proposed ID method is simple and efficient. The color uniformity performance can be tuned by selecting silicone with a proper surface tension without affecting the total correlated color temperature and sacrificing the WLED’s optical power.

In this study, a strongly reflective and photoluminescent (PL) poly(lactic-co-glycolic acid) quantum dot (QD) hybrid nanofiber (PQHN) structure is introduced to enhance the luminous efficacy of QD-phosphor hybrid white light-emitting diodes (QD-WLEDs). As the thickness of PQHN film increases, the PL is found to continuously increase, exhibiting a maximum peak intensity at 120 μm, which is 1.92 times that at 12 μm, and showing the highest diffuse reflectance of 94.4% at 640 nm. Consequently, while using the QD-WLEDs, the PQHN structure achieves a 53.8% improvement in luminous flux compared with the traditional structure under a similar correlated color temperature (CCT) of 3,540 K, achieving a high luminous efficacy of 202.11 lm W-1 for QD-WLEDs. In addition, the maximum deviation of the CCT is only 11 K when the current is changed from 50 to 950 mA, demonstrating good stability. Therefore, the PQHN films have great potential in lighting systems as a hybrid functional film including light conversion and reflectance.

This work aims to improve the thermal performance of a light emitting diode (LED) module by employing a novelly assembled heat pipe heat sink. The heat pipe was embedded into the heat sink by a phase change expansion assembly (PCEA) process, which was developed by both finite element (FE) analysis and experiments. Heat transfer performance and optical performance of the LED modules were experimentally investigated and discussed. Compared to the LED module with a traditionally assembled heat pipe heat sink, the LED module employing the PCEA process exhibits about 20% decrease in the thermal resistance from the MCPCB to the heat pipe. The junction temperature is 4% lower and the luminous flux is 2% higher. The improvement in the thermal and optical performance is important to the high power LED applications.

To further improve the luminous efficiency of LED lightings, this Letter proposes a chip-on-board (COB) device by combining diced staggered V-shaped patterns and remote phosphors. The results show that the V-shaped patterned COB (V-COB) with vertex angles from 120o to 150o can achieve a ∼17% output power increase (OPI) compared to the conventional COB. V-COB remote phosphor devices (RPDs) are then manufactured and tested. The luminous efficiency of the proposed RPD represents an 11.6% increase at the correlated color temperature of ∼3000 K. Such an improvement can be attributed to both the decreases of total internal reflections and phosphor backscatterings.

This paper proposes a novel multi-branch heat pipe (MBHP) that can be utilized for heat dissipation in multi-heat source electronics. The proposed heat pipe consists of three branches—two with an evaporator and one with a condenser—connected by vapor lines and liquid lines. A test system was implemented to study the filling ratio, the start-up characteristics, the power distribution characteristics, the dynamic characteristics and the thermal resistance of the heat pipe. The experimental results obtained indicate the following: 1) the optimal working fluid filling ratio of MBHP is between 75% and 100%; 2) the MBHP can start up steadily under tested heating load; 3) the ideal heat load of the MBHP (filling ratio 75%) was within a range of 30–160 W, in which the minimum total thermal resistance was 0.04 °C/W and the maximum temperatures of both evaporators were less than 110 °C under the limiting heating load of 160 W.

The remote phosphor caps (RPCs) have been studied theoretically and experimentally based on chip-on-board (COB) devices. We have investigated the effect of RPCs on the blue light and the yellow light emission distributions by ray-tracing. Moreover, the geometry of RPCs have been optimized to simultaneously achieve an excellent optical performance and color uniformity. Corresponding to simulation results, both the optimized (conical shape without straight side) and the reference (semi-spherical shape with straight side) RPCs have been manufactured by the compression molding method. These RPCs were assembled to the same blue COB source and then the COB devices have been measured. Compared with the reference RPC, the optimized RPC is able to significantly increase the radiant power and the luminous flux by 15.9% and 17.0% at a driving current of 350 mA, respectively, and it can also decrease the standard deviation of the correlated color temperature (CCT) by 48.9% for a total CCT about 4800 K. Hence, the proposed RPCs can provide a superior improvement in optical performance and color uniformity to COB devices.

Perovskite material has been widely researched for illumination. Since its shorter PL lifetime (nanosecond), compared with the traditional illumination phosphor (microsecond), perovskite has been considered as a promising material for communication. In this work, by ultrasonication, we synthesized the CsPbBr3 perovskite quantum dots and found that liquid perovskite quantum dots (LPQDs) presents shorter luminescence lifetime of 24ns than solid state perovskite (SPQDs). We demonstrated a white visible light communication (VLC) system by using the LPQDs as a color converter. The LD-based white lighting VLC system can reach a 1Gbps data rate at a receivable BER. Our study indicates that LPQDs has great potential in communication performance.

Quantum dot (QD) attracts great attention in light-emitting diode (LED) packaging for high-quality light sources, while it leads to low light efficiency due to the significantly high reabsorption loss between QDs. Accordingly, we experimentally study the reabsorption properties of QD color convertors (QCCs) for LED packaging considering various thicknesses and concentrations under different injection current. The results indicate the QCC configuration with a small thickness and large concentration can have the same absorption ability for chip light as that with the opposite configuration, resulting in the same QD light proportion. However, the QCC configuration having smaller thickness is more useful to decrease the reabsorption loss, leading to higher radiant power (an increase of larger than 37.2%). Moreover, it is essential to gain a high radiant power of QD light with small reabsorption loss, which can be realized by combining QCCs with a low QD content and a source with a large injection current. Based on this simple and effective approach, a conversion loss smaller than 20%, close to their quantum yield, can be achieved, which is approximately four times smaller than that gained by QCCs with a high QD content. However, it introduces additional radiant power of chip light, suppressing further improvement in the QD light proportion. Much work is still required to make full use of the redundant chip light. This study provides a better understanding of the reabsorption properties of QCCs and can significantly accelerate their applications in illumination and display applications.

All-inorganic cesium lead halide perovskite CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) have attracted significant attention owing to their fascinating electronic and optical properties. However, researchers still face challenges to achieve highly stable and photoluminescent CsPbX3 NCs at room temperature by the direct-synthesis method. Herein, we synthesize CsPbX3 NCs by a facile and environmentally friendly method, which uses an aqueous solution of metal halides to react with Cs4PbBr6 NCs via interfacial anion exchange reactions and without applying any pretreatment. This method produces monodisperse and air-stable CsPbX3 NCs with tunable spectra covering the entire visible range, narrow photoluminescence emission bandwidth, and high photoluminescence quantum yield (PL QY, 80%). In addition, the chemical transformation mechanism between Cs4PbBr6 NCs and CsPbX3 NCs was investigated. The Cs4PbBr6 NCs were converted to CsPbBr3 NCs first by stripping CsBr, and then, the as-prepared CsPbBr3 NCs reacted with metal halides to form CsPbX3 NCs. This work takes advantage of the chemical transformation mechanism of Cs4PbBr6 NCs and provides an efficient and environmentally friendly way to synthesize CsPbX3 NCs.

High-power laser illumination is considered as one of the most potential method for the next generation of lighting. However, heat accumulation greatly influences the optical performance of the phosphor converted layer, which is bottleneck of the high-power laser illumination system. In this study, a semiconductor chilling plate (SCP) with water cooling system was adopted to dissipate heat accumulated by phosphor convertor during the high-power blue laser excitation. Input laser power and the power of SCP were experimentally evaluated. The thermal and optical performances were also evaluated, respectively. As a result, the phosphor layer with a SCP showed better heat dissipation than the phosphor layer without a SCP. When the system was in the optimizing SCP substrate temperature (5℃), the highest input laser power that the phosphor layer with a SCP can sustain is 4.82W, which is 62.23% higher than the phosphor layer without a SCP (2.97W). Therefore, the phosphor layer with a SCP shows great potential in high-power laser illumination system.

Visible light communication (VLC) has attracted a lot of attentions. However, there are still some difficult issues need to be solved for practical applications, such as the small active area of the PD. The transmission distance and incident angle greatly affect the stability of VLC system. In this work, the influence of transmission distance, incident light angle and received optical power of receiver on VLC system has been investigated. In order to improve the performance of the receiver, series of hemispherical lenses for photodetector were analyzed. By fabricating suitable hemispherical lens, the signal to noise ratio (SNR) was measured under different condition, and the experiment results showed that the suitable hemispherical lens can well improve the communication performance of the VLC system.