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The 21st-century Maritime Silk Road (MSR) initiative provides a new direction for the high-quality development of China and the marine economy along the route. Studying the marine economy of the countries along the MSR will contribute to its sustainable development. This study used a slacks-based model (SBM) and considered undesired output to estimate the marine economic efficiency of 20 countries along the MSR from 2007 to 2017. The Malmquist-Luenberger productivity index model was applied to analyze the dynamic changes in and decomposition efficiency of marine economic efficiency. A dynamic panel model was employed to analyze the factors affecting efficiency. The results revealed that the overall marine economic efficiency of countries along the MSR trended upward from 2007 to 2017. The overall efficiency of the ocean at both ends of the MSR was greater than that in the middle and there was a clear difference in the marine economic efficiency of developed and developing countries. Moreover, as per the Malmquist-Luenberger productivity index model, the overall index demonstrated a fluctuating trend with the growth in the economic efficiency of countries along the MSR, which depend more on improvements in scale efficiency, and not on pure technical efficiency. Also, as shown by a dynamic panel model, degrees of resource dependence and levels of opening up have positive impacts on marine economic efficiency, while levels of economic development and the industrial structures have a negative impact. Therefore, countries along the MSR should actively adjust their industrial structures and attach importance to exchanges and cooperation that lead to maritime economic development.

Besides the junction temperature, phosphor temperature is another key parameter to characterize the thermal behavior of phosphor-converted light-emitting diodes (pc-LEDs). However, the measurement of phosphor temperature remains a challenge. In this paper, we proposed a modified bidirectional thermal resistance model for the junction and phosphor temperature estimation. Compared with the conventional thermal resistance model, both the heat generation of the phosphor layer and the heat flow through the phosphor layer were further considered in this model. Three LED packaging structures were fabricated and measured to complete the model. The heat generation of the chip and phosphor layer was measured. With varying driving current from 0.05 A to 0.65 A with an increment of 0.1 A, the maximum deviation of the predicted and measured junction and phosphor temperature is less than 1% and 9.2%, respectively, which proves the feasibility of the proposed model for the junction and phosphor temperature estimation.

Color performance is an important parameter for high-quality light-emitting diode (LED) lighting. Color-rendering index (CRI) and color quality scale (CQS) are two independent parameters to assess the color performance, but high CRI does not correspond to high CQS, and vice versa. Therefore, it's urgent to find a comprehensive and effective metric for assessing the color performance of LEDs that can simultaneously exhibit high color-rendering index (CRI) and high color quality scale (CQS) values. In this study, a genetic algorithm with a penalty function was proposed for realizing spectral optimization by boosting the maximum attainable luminous efficacy of radiation (LER) of spectra while constraining both high CRI and CQS. By simulations, white spectra from LEDs with CRI≥95 and CQS≥95 were achieved at different correlated color temperatures (CCTs) from 2020 K to 7929 K. Further, a real spectra-tunable LED module consisting of four LEDs is fabricated, and high LER (344 lm/W) and color performance (CRI≥90, CQS=90) was realized by tuning driving currents.

Phosphor temperature in high-power white light-emitting diodes can greatly affect the optical properties, reliability, and lifetime. Accurate estimation of phosphor temperature is the first step for enhancing thermal management inside the package. In this paper, the phosphor temperature was measured by a plug-in method with thermocouple. The thermocouple’s bead was inserted into the phosphor layer, and then the silicone matrix got cured. The phosphor temperature was measured under various input currents. Under 350 mA, the temperature difference between the measured value and the junction temperature was about 17 °C higher than those in the references. The reason for this overestimation was attributed to light energy absorption and conversion of the bead, which was confirmed by thermal simulations.

Light-emitting diodes (LEDs) are widely used in our daily lives. Both light and heat are generated from LED chips and then transmitted or conducted through multiple packaging materials and interfaces. Part of the transmitted light converts into heat along the light propagation; in return, the accumulation of heat leads to the degradation of light output. The accumulated heat negatively influences the reliability and longevity of LEDs, and thus thermal management is critical for LED packaging and applications. On the other hand, in LED packaging processes, many fluid flow problems exist, such as phosphor coating, silicone injection, chip bonding, solder reflow, etc. Among them, phosphor coating is the most important process which is essential for LED performance. Phosphor gel is a kind of non-Newton fluid and its coating process is a typical fluid-flow problem. Overall, since LED packaging and applications present many heat and fluid flow problems, obtaining a full understanding of these problems enables advancements in the development of LED processes and designs. In this review, the emphasis is placed on heat generation in chips, heat flow in packages and application products, fluid flow in phosphor coating process, etc. This is a domain in which significant progress has been achieved in the last decade, and reporting on these advances will facilitate state-of-the-art LED packaging and application technologies.

In this letter, we proposed a remote phosphor coating method by lens wetting for enhancing the angular color uniformity of phosphor-converted white light-emitting diodes. Simulations based on the volume of fluid (VOF) method were applied to investigate the geometry evolution of a phosphor gel droplet after being dropped onto the lens, and the stable geometry of the phosphor gel was obtained. Monte Carlo ray tracing was used to study the optical performance of LED samples with the stable phosphor geometries. Besides, experiments were conducted to verify the fabrication flexibility of the proposed method. The VOF simulation and experimental results show that the proposed method can realize the hemispherical remote phosphor layers with uniform or non-uniform thickness by adjusting the coating volume. The optical simulations and the experimental measurements show that the LED samples with non-uniform thickness remote phosphor geometry achieves smaller correlated color temperature deviation (

In this letter, remote quantum dot phosphor-converted light-emitting diodes (QD-LEDs) with air encapsulation, silicone lens, and silicone encapsulation were fabricated. The effects of different packaging methods on the optical and thermal performances of QD-LEDs were evaluated based on the experimental tests and simulation. Optical efficiency and spectral stability were tested by experiment, and the temperature was assessed by finite-element simulation and infrared thermal imager tests. It was found that the silicone encapsulation type could convert more blue light into QDs emission light due to the reabsorption of backward reflected blue light. The silicone encapsulation type showed only a 6.2% decrease in QDs emission peak intensity when the driving current varied from 50 to 500 mA, while the silicone lens type dropped by 20.4% and the air encapsulation dropped by 36.8%. It was also confirmed that the QDs temperature in silicone encapsulation was 24 °C lower than those in the air encapsulation type and the silicone lens type at driving current of 300 mA.

Droplet bouncing on surfaces has long been observed in nature and industry, which is rather intriguing and instructive for related technology development. Recent decades have witnessed significant progress on the mechanism exploring, device development, and application demonstrations. In this review, we focus on the recent progresses that aim at introducing the phenomena, revealing the underlying physics, and promoting the potential applications of water droplet bouncing on various solid and soft surfaces like hydrophobic/hydrophilic/heated solid surfaces and liquid film/bath/droplet. The water droplet bouncing dynamics is highly dependent on the liquid properties, surface characteristics and ambient pressure. The absence of droplet/surface contact, as the key point for droplet bouncing, can be realized by lowering the Weber number of droplet and designing hydrophobic surfaces to reduce the droplet-surface contact, actively maintaining the air/vapor film by heating the solid surface above the Leidenfrost point, vibrating the liquid bath, applying electric/magnetic/pressure fields, etc. Moreover, the comprehensive understanding of droplet bouncing has promoted the development of numerous advanced surfaces technologies, including surface self-cleaning, directional droplet transportation, heat transfer enhancement, droplet logic gate, electrical generation and so on. Finally, the future directions for research and application are outlined and discussed.

Narrowband mid-infrared emitters, quantified by the Q -factor, have garnered a lot of attention due to their emerging applications from chemical and biosensing to efficient thermal utilization. Previous studies reported high Q -factor emitters within several selected wavelengths, still lacking a large database of emitter structures with very high Q -factors. In this Letter, we utilized the Monte Carlo Tree Search (MCTS) algorithm under the framework of material informatics to optimize the Tamm emitters at the infrared range (from 3 to 10 µm) for achieving a high Q -factor and high emissivity simultaneously, providing a large database of high and sharp emission peaks in the infrared. Through the MCTS algorithm, the structure with a Q -factor of 508 and an emissivity peak of 0.92 at 4.225 µm is obtained, far surpassing the previous results, and the underlying mechanism is discussed by electric field simulations. The high Q -factor emitters in the database show good monochromatism and high emissivity, accelerating the selection of proper perfect emitters for desired wavelengths. This Letter also paves a feasible avenue for the emitter and absorber design with ultrahigh monochromatism.

Next generation high-power Light–Emitting Diodes (LED) require specialized cooling systems for ensuring performance and reliability. The ability of a multi-jet single-phase liquid cooling system (jet diameter 400 µm) for thermal management of the high-power LED based luminaire is investigated and successfully demonstrated for a 300 W nominal power module. Operating pressure of the jet system is varied in the range of 0–8 bar, leading to coolant water flow rates varying from 65 ml/min to 782 ml/min (Re = 3833–46 119). With the proposed multi-jet cooling system, the experiments show the possibility of maintaining the module surface temperature well below 70 °C for substrate level heat flux up to ~125 W/cm2. We show that the system can still maintain safe operating temperature, without loss of luminous efficiency for input power up to 130% of the nominal design power. Supporting detailed three-dimensional numerical simulations of the conjugate module heat transfer inside the LED package volume are provided. It is concluded that single-phase array of water-based jet flow is an excellent potential option for thermal management of high-power LED luminaire.

Light Emitting Diodes (LEDs) are getting popular due to their wide applicability in various domestic and industrial applications. However, the advent of high-power LEDs is accompanied with the critical issue of higher heat power management, coupled with enhanced flux levels. Natural and forced convection techniques with air as the working fluid are unable to provide thermal management at required operating safe temperatures in several upcoming compact LED array designs. Hence, there is substantial advancement in the development of thermal management solutions for the packaging of high-power LEDs. Liquid jets and sprays are potential candidates which need further exploration, especially from a point of view of packaging with LED modules. Both configurations can operate in single-phase and two-phase boiling regimes. While considerable literature is available on single-phase liquid jets, liquid sprays pose several challenges in terms of flow parameter management and associated transport physics. In this paper, we review nuances of the latter technology, i.e., spray cooling technique, crucial for thermal management of LEDs. A comprehensive overview of flow distribution and heat transfer during impingement of liquid sprays on heated surfaces is presented from the viewpoint of temperature control of high power LED sources. Additionally, the data presented will help in developing a configuration design of a liquid spray-based thermal management system integrated with high heat flux devices.

Phase-change materials (PCMs) have attracted numerous attentions in thermal energy storage area due to their high latent heat capacity. However, their inherently low thermal conductivity and potential leakage risk severely decrease the thermal storage efficiency. In this study, thermally-enhanced nanoencapsulated phase change materials (NEPCMs) were proposed to overcome those limitations. Through a miniemulsion polymerization approach, the n-Octadecane is encapsulated by SiO2/BN shell, which not only enhances the thermal conductivity, but also avoids the leakage problem during the phase change process. Compared with pristine PCMs, the thermal conductivity of the prepared NEPCMs was reinforced by 527% to 0.912 W m−1 K−1, which is the highest record among all the encapsulated PCMs with encapsulation ratio above 50%. The latent heat of the NEPCMs reaches 136.8 J/g with an encapsulation ratio as high as 60.4%. The thermal gravity analysis (TGA) and thermal cycling tests reveal that the nanocapsules possess excellent thermal stability and reliability. Furthermore, the NEPCMs were applied in latent functionally thermal fluid (LFTF) to enhance its thermal storage capacity. A microchannel cooling setup, with the NEPCMs/water LFTF as the coolant, was developed to evaluate the LFTF cooling performance. Compared with the pristine water, LFTF with 20 wt% NEPCMs reduced the heat source temperature by 12.1 °C at 80 W, showing their potential for the thermal management applications in electronic devices.

The advent of transformation thermotics has seen a boom in development of thermal metamaterials with a variety of thermal functionalities, including phenomena such as thermal cloaking and camouflage. However, most thermal metamaterials-based camouflage devices only tune in-plane heat conduction, which may fail to conceal a target from out-of-plane detection. We propose an adaptive radiative thermal camouflage via tuning out-of-plane transient heat conduction, and it is validated by both simulation and experiment. The physics underlying the performance of our adaptive thermal camouflage is based on real-time synchronous heat conduction through the camouflage device and the background plate, respectively. The proposed concept and device represent a promising new approach to fabrication of conductive thermal metamaterials, providing a feasible and effective way to achieve adaptive thermal camouflage.

The thermoelectric properties of monolayer Tl 2 O are studied using first-principles calculations with all involved electrical and thermal transport properties calculated in the parameter-free frameworks. It is found that monolayer Tl 2 O possesses remarkably high thermoelectric figure of merit, z T, due to its ultralow lattice thermal conductivity and fairly good power factor. The room temperature z T can be as high as 1.4 and 1.2 for n- and p-type systems, respectively, whereas the maximum z T values can reach up to 5.3 and 4.2 as the temperature increases to 800 K. In addition, it is clarified that the mobilities of monolayer Tl 2 O are orders of magnitude smaller than previous estimation from simplified semiempirical models. The room temperature electron and hole mobilities are only about 56 and 11 cm 2 V − 1 s − 1, respectively, due to the heavy effective mass along with strong polar optical phonons coupling scattering. Nonetheless, the intrinsically ultrahigh z T from entire first-principles calculations stimulate that the further experimental verification and exploration for practical application are worthwhile.

As a direct approach to utilize the abundant solar energy, solar steam generation surges in recent decade to generate fresh water from sewage and seawater, while still suffering from challenges like a limited photothermal efficiency and scale manufacturing. To enhance the solar energy utilization efficiency, inspired from banyan tree, we demonstrate a new, scalable and low-cost hierarchical evaporator, comprising an activated carbon-cotton fabric as photothermal leaves, commercial polyester pillars as prop roots, and expandable polyethylene foams, to largely utilize solar energy. The both sides of fabric and lateral area of polyester pillars collectively contribute to a rather high evaporation rate 1.95 kg m−2 h−1, with enhanced solar efficiency under 1 sun illumination. Polyester pillars as water paths can reduce the contact area between the photothermal layer and bulk water to prevent heat loss. The hierarchical evaporator is able to enhance solar energy utilization by increasing the extra evaporation area including the bottom side of fabric and lateral area of polyester pillars and thus behave most similarly to the transpiration process of banyan tree from both sides of leaves and prop roots. Moreover, the proposed hierarchical evaporator is further demonstrated to possess anti-salt-clogging performance by changing the number of polyester pillars. The banyan-inspired hierarchical evaporator is scalable, feasible, and low-cost, showing great potential for direct industrial applications of solar energy on clean water generation and sewage treatment.

The electrical transport properties of β-Ga2O3 are studied by first-principles calculations. The calculated intrinsic electron Hall mobilities agree well with experiments, with intrinsic Hall factor decreasing monotonically from 1.54 at 100 K to 1.14 at 800 K. The anisotropy of electron mobility is weak due to the almost isotropic electron effective mass, which also results in nearly isotropic Seebeck coefficient and electronic contribution to the thermal conductivity. The mode analysis of phonon scattering reveals that the optical phonon scattering is almost entirely determined by the long-range polar interactions, whereas the acoustic phonon scattering also plays an important role especially at low temperatures. The intrinsic electron mobility is significantly overestimated even above room temperature by only considering the polar optical phonon scattering, in contrast to previous predictions from fitting of phenomenological models.

Illusion thermotics, which aims at creating temperature fields to mislead a thermal detector, encompasses many thermal functionalities. It has attracted significant attention due to the increasing number of promising applications. Transformation thermotics and scattering cancellation methods are frequently adopted for illusion devices, though they have inherent defects such as anisotropic thermal properties and complicated fabrication methods. Here, we present a general framework for topology optimization, which can be used to design the structure of an illusion device automatically. The optimized configuration can camouflage the thermal exterior of an illusion device so that it is identical to a reference. The original heat source can drive the virtual heat source despite the structure being simply composed of natural materials. To establish an effective topology optimization model, a volume constraint was imposed on the total volume of iron and a prescribed objective function was used to evaluate the difference between the reference temperature and the temperature field during the topology optimization. The flexibility of the method presented was successfully validated by changing the total volume of iron, the number and locations of the thermal illusions, the types of composite materials, and the original heat sources. Topology optimization is a new and flexible approach for designing thermal metamaterials and metadevices for diverse thermal functionalities and beyond.

In polar compounds, Frohlich interaction plays an important role in electrical transport, and it is highly dependent on the dimensionality. In two-dimensional (2D) materials, Frohlich interaction cannot be correctly described by the analytical model available for bulk materials, which prevents the employment of the state-of-the-art first-principles calculation of electrical transport based on maximally localized Wannier functions interpolation. Recently, an approximate 2D Frohlich model with screened dielectric properties is proposed. Selecting the strong polar material of monolayer InSe, we examine the accuracy of this 2D Frohlich model by comparing the electron mobility calculated using this model with that based on direct density functional perturbation theory calculations of 2D Frohlich interaction. It is found that the 2D Frohlich model can guarantee fairly good results with an advantage of tremendously reduced computational consumption. Using this model, the modulation of the electron mobility of monolayer InSe by the dielectric environment is studied. The electron mobility can be drastically enhanced by coating high-dielectric materials, with room-temperature mobility improved from about 100 c m 2 V − 1 s − 1 to about 500 c m 2 V − 1 s − 1, due to the strong suppression of Frohlich scattering.

Light-matter interaction upon nanophotonic structures in the infrared wavelength has drew increasing attentions due to the extensive potential applications. Among them, thermophotovoltaic (TPV) systems can exhibit higher efficiency over the Shockley-Queisser limit due to the nanophotonic structure-enabled tunable narrowband thermal emission rather than the broadband incident spectrum. However, two long-standing issues remain formidable as bottlenecks for achieving better performances of TPV system. One is the competing role of the power density and the system efficiency of TPV system, and the other is the magnanimity possibilities of structures, configurations, dimensions, and materials of thermal emitters that disables the manual optimization of TPV system. Here, we attempt to achieve high-performance TPV system by employing the machine learning algorithm under the framework of material informatics. The power density and system efficiency are well modelled through the detailed balance analysis with full considering the photocurrent generation in the PV cells. Through optimization, the non-trial aperiodic Tamm emitters are obtained and the metal-side one is preferable in terms of the TPV performance. The present work is demonstrated to be feasible and efficient in optimizing the TPV performance, and opens a new door for the optimization problems in other fields.

The diffusive nature of heat flow lays a formidable obstacle for directional heat manipulation, not akin to the wave-governed electromagnetics that can be well controlled in intensity and direction. By modulating the near-field radiative heat transfer among graphene/SiC core-shell (GSCS) nanoparticles, we propose the concept of thermal routing to address the directional heat manipulation in a particular many-body setup. The graphene shell introduces a minor polarizability peak and remarkably modifies the localized surface resonance of the particle, which plays a significant role in the radiative heat transfer within the many-body system consisting of GSCS nanoparticles. Consequently, Fermi levels of graphene shells matching allows directional radiative heat flow, thus enabling thermal routing manifested by variant designated temperature distributions. The proposed thermal routing could be used to dynamically tune heat flow in integrated nano-objects for thermal manipulation, and also opens avenues for exploiting novel thermal functionalities via radiative heat transfer at the nanoscale.

Artificially structured thermal metamaterials provide an unprecedented possibility of molding heat flow that is drastically distinct from the conventional heat diffusion in naturally conductive materials. The Laplacian nature of heat conduction makes the transformation thermotics, as a design principle for thermal metadevices, compatible with transformation optics. Various functional thermal devices, such as thermal cloaks, concentrators, and rotators, have been successfully demonstrated. How far can it possible go beyond just realizing a heat-distribution function in a thermal metadevice? Herein, the concept of encrypted thermal printing is proposed and experimentally validated, which could conceal encrypted information under natural light and present static or dynamic messages in an infrared image. Regionalization transformation is developed for structuring thermal metamaterial-strokes as infrared signatures, enabling letters of the alphabet to be written, paintings to be drawn, movies to be made, and information to be displayed. This strategy successfully demonstrates an extreme level of manipulation of heat flow for encryption, illusions, and messaging.

Optical and thermal metamaterial-based structures have been extensively explored, yielding many interesting functionalities; in what other ways can they be used? This study, following the basic rules of transformation optics (here thermotics), demonstrates another application: thermal encoding, based on binary states of heat flux for bit values of 0 and 1, by means of thermal energy shielding and harvesting units. This approach is a fresh alternative to existing implementations for thermal memory or computing.

In this study, we proposed a flexible method to realize a cylindrical tuber encapsulant layer. Firstly, patterned LED substrate with silicone-wetting and silicone-repellency surfaces was prepared by depositing low surface energy modified nanosilica particles. Secondly, coating phosphor gel onto the LED chip. Thirdly, coating the encapsulant (silicone OE6550A/B) onto the phosphor gel layer. The silicone stops spreading at the border of silicone-wetting and silicone-repellency surfaces and its final contact angle can be adjusted to any value between the contact angle of silicone-wetting and silicone-repellency surface, so it is very easy to realize dome-shape silicone layer with contact angle of ∼90°. For COB-LEDs with LED array in series, the final silicone layer geometry is similar to the cylindrical tuber. The results show that compared to the conventional flat encapsulant layer, the proposed encapsulant layer can improve the light efficiency by > 60% for pure blue light and 13.6% for white light at correlated color temperature (CCT) of ∼5500K.

The behaviors of the light propagation in the phosphor play a vital role in determining the optical performance of the phosphor-converted light-emitting diodes (pc-LEDs). In this paper, we presented a general model based on the radiative transfer equation integrated with fluorescence (FRTE) to describe the overall light propagating properties in the phosphor layer in terms of light absorption, strong forward scattering, and fluorescence. The model was established by accounting for general boundary conditions including the LED Lambertian incidence, the diffuse reflection at the substrate/reflector, and the Fresnel reflection at the phosphor-air interface. The spectral element method (SEM) was extended to numerically solve FRTE. The radiant intensity at any location and direction of blue and yellow light was iteratively calculated, in which case the angular properties could be further evaluated. The model was validated by comparing the light extraction efficiency (LEE) and angular correlated color temperature (CCT) calculated by the presented model with the experimental results. Good agreements were achieved between model predictions and measurements with the corresponding maximum deviation of 4.9% and 3.7% for LEE and CCT, respectively. We also conducted a comparison between our model and the previous Kubelka-Munk (KM) theory. It has been revealed that the KM theory may overestimate the phosphor heating due to lacking of the blue light scattering effect.

The displacement of the LED chip can easily occur during chip bonding process, which is the first step of LED packaging. In this work, the effect of LED chip's displacement was studied by theoretical analysis and a series of comparative experiments, and the effects include LED's optical performance and reliability. LED modules with different chip displacement distances were packaged. The optical parameters were measured and accelerated aging tests were conducted to estimate the LED modules’ reliability. The degradation curves of luminous power were fitted and the lifetimes were predicted. It was found that the chip displacement can greatly affect the optical performance and reliability of LED modules. Finally, some possible methods to eliminate the effect were brought up.

Phase change materials (PCMs), due to their extraordinary latent heat storage characteristic, have been widely investigated in the thermal management of electronic devices. However, the current PCM-based heat sinks generally suffer a long heat dissipation time after heat absorption. To address this issue, the modularized thermal storage unit (MTSU) was proposed in this paper. The online charging and offline discharging working modes of the MTSU allow it to cool the intermittent electronic devices with a high duty cycle. In this paper, the MTSU samples were fabricated with paraffin wax as latent heat storage core unit and polymer encapsulation shell. The specific latent heat storage and morphology of the MTSU samples were studied. Afterward, the thermal storage performance of each individual MTSU sample was specially characterized with the sample subjected to the constant heat flux. The MTSU samples showed desirable performance on encapsulating the PCMs and stabilizing the heat source temperature. The safe operation time of the heat source was prolonged by 181% with 16 g of PCM in the vacuum environment. Furthermore, the performance of the MTSU samples on cooling of the electronic devices with a relatively high duty cycle was investigated. The results show that owing to the modularization and replaceability of the samples, the ON/OFF working time ratio of the heat source was greatly enlarged. When cooled by the MTSU sample with 11.42 g of paraffin, the heat source could work with an ON/OFF time ratio up to 6.7 at 4 W and 14.9 at 3 W.

Many high-power electronic devices such as high-power light-emitting diodes and aerial devices work intermittently. If some of the heat generated by the chips could be stored in the thermal storage medium during the working time and then be released to the ambient in the nonworking time, the heat dissipation load of the heat sinks could be diminished and a better thermal characteristic could be achieved. Inspired by this idea, we proposed a thermal storage substrate and investigated its thermal storage properties by experiment in this study. First, the composite phase-change material (CPCM) was prepared as the thermal storage medium. Second, the thermal and phase-transition properties of the CPCM were studied through differential scanning calorimeter tests. Third, the thermal conductivity of the CPCM was measured for the analysis of thermal performance. Afterward, the CPCM-based substrate was fabricated and several experiments were conducted to examine its thermal storage performance. The results showed t...

In this letter, we studied the effect of chip offset on the optical performance of bare chip and white light-emitting diode (LED) package through a series of comparative experiments. LED modules with different chip offset distances were packaged and measured. The results show that chip position offset has a great influence on white LED’s performance. When the offset distance reaches 1 mm, the luminous efficiency decreases by 22.9% and the angular color distribution is deteriorated. Two methods are recommended to avoid this effect.

"Fata Morgana" or "Mirage" phenomena have long been captivated as optical illusions, which actually relies on gradient-density air or vapor. Man-made optical illusions have witnessed significant progress by resorting to artificially structured metamaterials. Nevertheless, two long-standing challenges remain formidable: first, exotic parameters (negative or less than unity) become inevitable; second, the signature of original object is altered to that of a virtual counterpart. It is thus not able to address the holy grail of illusion per se, since a single virtual object still exposes the location. In this study, those problems are successfully addressed in a particular setup-illusion thermotics, which identically mimics the exterior thermal behavior of an equivalent reference and splits the interior original heat source into many virtual signatures. A general paradigm to design thermal illusion metadevices is proposed to manipulate thermal conduction, and empower robust simultaneous functions of moving, shaping, rotating, and splitting heat sources of arbitrary cross sections. The temperature profile inside the thermal metadevice can mislead the awareness of the real location, shape, size, and number of the actual heat sources. The present concept may trigger unprecedented development in other physical fields to realize multiple functionalized illusions in optics, electromagnetics, etc.

In the phosphor coating process of the phosphor-converted light-emitting diodes (pc-LEDs) packaging, the phosphors settle spontaneously due to the density difference between the phosphor particles (YAG-04, about 4800 kg/m3) and the silicone matrix (OE6550 A/B, about 1120 kg/m3). The phosphor sedimentation affects the phosphor distribution and changes the optical performance of pc-LEDs, such as the luminous efficiency (LE) and correlative color temperature (CCT). Therefore, a deep understanding of the phosphor sedimentation effect on the optical performance of pc-LEDs is urgent needed. In this study, we applied an online testing experimental setup to investigate effect of the substrate temperature on the phosphor sedimentation of pc-LEDs. LED substrate was heated to a pre-defined temperature before the phosphor gel been coated, a range of substrate temperature from 30 °C to 100 °C with a step of 10 °C was investigated. The results show that the substrate temperature can accelerate or diminish the phosphor sedimentation, when temperature increases from 30 °C to 100 °C, the CCT variation decreases from 39.62% to 0.27%, and the LE variation decreases from 4.08% to 0.21%.

In phosphor-converted light-emitting diodes (pc-LEDs), phosphor heating can lead to decrease of luminous efficiency or even thermal quenching due to local high phosphor temperature. Phosphor scattering model has been used to calculate the phosphor heat generation. Using this model, there are two methods for heating power estimation, one is the subtractive method and the other is the integral method. In this work, we conducted comparative study of these two methods. We found the heating power of integral method is lower than that of the subtractive method. Phosphor heat generation measurement was performed and results showed that the experimental data agreed well with the subtractive method. Finite element model (FEM) was used to evaluate the phosphor temperature by inputting the calculated heating power. Higher phosphor temperature was obtained by the subtractive method due to relative higher heat load. Infrared thermal test verified that the measured phosphor temperature was close to that of the subtractive method. Therefore, the phosphor scattering model using the subtractive method can be applied for accurate phosphor heating and temperature estimation.

Human comfort has become one of the most important criteria in modern lighting architecture. Here, we proposed a tuning strategy to enhance the non-image forming photobiological effect on the human circadian rhythm based on quantum-dots-converted white light-emitting diodes (QDs-WLEDs). We introduced the limiting variability of the circadian action factor (CAF), defined as the ratio of circadian efficiency and luminous efficiency of radiation. The CAF was deeply discussed and was found to be a function of constraining the color rendering index (CRI) and correlated color temperatures. The maximum CAF variability of QDs-WLEDs was found to be dependent on the QDs' peak wavelength and full width at half maximum. With the optimized parameters, the packaging materials were synthesized and WLEDs were packaged. Experimental results show that at CRI > 90, the maximum CAF variability can be tuned by 3.83 times (from 0.251 at 2700 K to 0.961 at 6500 K), which implies that our approach could reduce the number of tunable channels, and could achieve wider CAF variability.

This study quantitatively analyzed the optical and thermal performances of remote quantum dots (QDs)-based white light-emitting diodes (QDs-WLEDs) with the same spectra power distribution (SPD) but reverse packaging structures. The output optical power and PL spectra were measured and analyzed by an integrating sphere system, and the temperature fields were simulated by combing optical measurement with thermal simulation, finally the temperature fields were validated by infrared thermal imager. It was found that when achieved identical SPD, the QDs-on-phosphor type achieved LE of 112.2 lm/W, while the phosphor-on-QDs type demonstrated lower LE of 101.4 lm/W. Moreover, the QDs-on-phosphor type generated less heat than that of another, consequently the highest temperature in the QDs-on-phosphor type was lower than another, and the temperature difference can reach 11.2°C at driving current of 160 mA. Therefore, the QDs-on-phosphor type is an optimal packaging architecture for higher optical efficiency and lower device temperature.

In this study, genetic algorithm (GA) was utilized to optimize the phosphor distribution to decrease the junction temperature of white phosphor-converted light-emitting diodes (pc-LEDs). The key steps of the GA were introduced, including selection, crossover, and mutation. Both the junction temperature and the entransy dissipation of each evolution were calculated. It was found that with evolutions, the phosphor particles tend to build a “thermal bridge” between the chip and the convective boundary and spread along the convective boundary. The junction temperature decreases from ∼157.5 °C to ∼150 °C and the entransy dissipation decreases from ∼18 W K to ∼6 W K. The least entransy dissipation principle was demonstrated to be the rule that governs the optimization processes.

Phosphor heat generation in phosphor-converted light-emitting diodes (pc-LEDs) plays an important role in affecting the optical and thermal performance of LEDs, but it is hard to measure directly. In this paper, we developed a method to calculate the phosphor heat generation by modifying the Kubelka–Munk theory. With full consideration of light scattering, absorption and conversion inside the phosphor layer simultaneously, we calculated the phosphor heat generation and analyzed its trend with changing the phosphor quantum efficiency and phosphor parameters (concentration, thickness, particle size). Experiments were also conducted to validate the calculations. It was found that with the increase of phosphor concentration from 0.11 to 0.34 g/cm 3 , the total energy loss increases by 54.11%. The phosphor concentration and thickness played similar roles in affecting the phosphor heat generation. The maximum phosphor heat generation corresponded to the phosphor particle size of around 2 μm, which is denoted as the critical size.

Acquiring the junction temperature of light emitting diode (LED) is essential for performance evaluation. But it is hard to get in the multipleLED applications. In this paper, an engineering method is presented to estimate the junction temperatures of LEDs in multiple LED applications. This method is mainly based on an analytical model, and it can be easily applied with some simple measurements. Simulations and experiments were conducted to prove the feasibility of the method, and the deviations among the results obtained by the present method with those by simulation as well as experiments are less than 2% and 3%, respectively. In the final part of this study, the engineering method was used to analyze the thermal resistances of a street lamp. The material of leadframe was found to affect the system thermal resistance mostly, and the choice of solder material strongly depended on the material of the leadframe.

This paper reports a new way to conduct fracture mechanics experiments of welded thin-walled structure for aircraft fuselage applications made of the Al 6156 ally using lock-in infrared thermography. The heat wave, generated by both the themo-mechanical coupling and intrinsic energy dissipation was detected by an infrared camera. The crack growth rate measured by the lock-in infrared thermography is found to be consistent with that measured by conventional method. It is observed that the crack can either grow underneath the stiffener or grow into the stiffener web with the crack length measured at the same time. In addition, the crack tip plastic zone was observed before the specimen was about to be destroyed.