Laser-driven white light illumination is considered as the next generation of high brightness white light source. The most common way to achieve laser-based white light is using a blue laser to ...excite phosphor/ silicone converter (reference converter). However, the relatively low thermal conductivity of phosphor limits most of the heat to its surface and cannot be dissipated effectively. In this work, a converter with copper sintering powder framework/paraffin (CPSF/P) embedded into the phosphor/silicone is proposed. As an internal heat transfer channel, copper powder sintering framework (CPSF) transfers heat to paraffin coated in porous skeleton, and then paraffin absorbs the generated heat through solid-liquid phase transition, which effectively dissipates the heat concentrated on the phosphor surface and improves its thermal stability. Under high-power laser excitation of 7.74 W, the surface temperature of the reference converter is up to 660 °C, while the maximum temperature of the CPSF/P converter is only 139 °C, which is reduced by 521 °C (78.9%). The results show that the proposed CPSF/P converter can withstand higher excitation power and show better thermal stability than the reference converter, which is helpful to obtain higher color stability. This provides an efficient heat dissipation scheme for high-power laser-driven lighting.
Quantum dots (QDs) are usually used with phosphor to obtain white light-emitting diodes (WLEDs) due to their excellent lighting characteristics. For lighting effect improvement, the QDs layer and the ...phosphor layer are supposed to be separated to reduce reabsorption loss and enhance QDs stability. Based on the separated structure, a QDs/boron nitride hybrid reflective (QBHR) structure is proposed to enhance the optical performance of WLEDs in this study. QDs were electrostatically bonded on the boron nitride (BN) pellets and their composite particles were subsequently mixed with silicone for LED encapsulation by a spinning-coated process. It could be easily managed the performance of QBHR structure by controlling the composite particles' concentration or centrifugal speed. The diffuse reflectance and photoluminescence (PL) intensity of QBHR structure with various thicknesses were analyzed. While applying with remote phosphor layer for WLEDs, the luminous efficacy of devices with QBHR structure increases with phosphor concentration, which are larger than that of QD/polydimethylsiloxane (QP) structures. It may be caused by the light extraction ability of the scattering BN particles and high color conversion efficiency (CCE) of QBHR structure. Finally, under the same correlated color temperature (CCT) of 3640 K, the luminous efficacy and CCE enhance by 14.2% and 19.5% using the QBHR structure, respectively. In addition, the QBHR structure shows better stability than the QP structure after aging for 387.75 h. In brief, the QBHR structure shows an effective and practical packaging method to produce high-performance WLEDs.
Ultraviolet light-emitting diodes (UVLEDs) used as excitation sources for quantum dots (QDs) are promising candidates for the display field. To eliminate the residual excitation light, the ...conventional method is simply increasing the optical density of QDs for packaging, which would significantly reduce the luminous efficiency of QD-light-emitting diode (LED) devices owing to reabsorption loss. In this study, the combination strategy of a boron nitride (BN) reflective coating and an ultraviolet-reflection filter (UV-R filter) for QD-LED devices is proposed. By managing the recycle of UV light to excite more QDs and reducing the reabsorption effect of QDs carefully, their green emission intensity of LED using such a strategy is 82.0% higher than that of a conventional device with a similar QD light energy proportion of ~99.0% (almost no residual UV excitation light). This strategy is also effective for red QD-LED devices while eliminating residual UV excitation light and enhancing the red emission intensity. Therefore, this study provides an effective way to develop QD-LED devices with high QD emission intensity and low UV light leakage for display.
Ultra-thin vapor chambers (UTVCs) are widely used to cool high-power electronics due to their excellent thermal conductivity. In this study, a UTVC of 82 mm × 58 mm × 0.39 mm with composite wick was ...prepared. The composite wick is composed of two layers of copper mesh and multiple spiral-woven meshes (SWMs), and the composite wick was applied in UTVC to improve liquid replenishment performance and temperature uniformity. Furthermore, the thermal performance of UTVCs with different support column diameters, filling ratios (FRs), and SWM structures was experimentally studied. The results found that the equivalent thermal conductivity (ETC) decreases as the diameter of the support column increases; the UTVC with 0.5 mm support column diameter has the highest ETC, at 3473 W/(m·K). Then, the effect of FR on the heat transfer performance of UTVCs with SWM numbers of 0, 1, 2, and 3 (0 SWMs, 1 SWM, 2 SWMs, 3 SWMs) is consistent, the 30% FR UTVC with 3 SWMs having the highest ETC, at 3837 W/(m·K). Finally, the increased number of SWMs can significantly improve the ultimate power of the UTVCs, the UTVC with 3 SWMs having the highest ultimate power, at 26 W. The above experimental studies indicate that the designed and manufactured UTVCs have great potential advantages in thermal dissipation for electronics.
Ultraviolet light-emitting diodes (UVLED) are a new type of device in the LED development; however, the radiant efficacy of UVLEDs is still too low to satisfy the requirements of applications. In ...this study, boron nitride nanoparticles (BN NPs) are incorporated into the UVLED’s silicone encapsulation to improve the optical output power. This BN NPs-based package shows an increase in optical flux of 8.1% compared with silicone-only encapsulation when the BN NP concentration is optimized at 0.025 wt%. By analyzing the BN NP film, adding the BN NPs into silicone leads to a decrease in transmittance but an increase in haze. Haze and transmittance has an excellent negative correlation with increasing BN concentration under 365 nm. The moderate BN NP concentration maximizes the scattering performance from haze while maintaining high transmittance. Therefore, this enhanced light output is attributed to scattering that reduces optical losses from total internal reflection at the silicone–air interface. By using the new BN-based structure in green and red quantum dot devices, an increase radiant flux of the device is observed, 9.9% for green LED and 11.4% for red LED. This indicates that BN NPs have potential prospects in the application of UV LEDs used as excitation sources for quantum dots.
The ability to precisely obtain tunable spectrum of lead halide perovskite quantum dots (QDs) is very important for applications, such as in lighting and display. Herein, we report a microchannel ...reactor method for synthesis of CsPbBr₃ QDs with tunable spectrum. By adjusting the temperature and velocity of the microchannel reactor, the emission peaks of CsPbBr₃ QDs ranging from 520 nm to 430 nm were obtained, which is wider than that of QDs obtained in a traditional flask without changing halide component. The mechanism of photoluminescence (PL) spectral shift of CsPbBr₃ QDs was investigated, the result shows that the supersaturation control enabled by the superior mass and heat transfer performance in the microchannel is the key to achieve the wide range of PL spectrum, with only a change in the setting of the temperature controller required. The wide spectrum of CsPbBr₃ QDs can be applied to light-emitting diodes (LEDs), photoelectric sensors, lasers, etc.
Light-emitting diode (LED) combined with quantum dots (QDs) is an important candidate for next-generation high-quality semiconductor devices. However, the effect of the excitation wavelength on their ...optical performance has not been fully explored. In this study, green and red QDs are applied to LEDs of different excitation wavelengths from 365 to 455 nm. The blue light is recommended for exciting QDs from the perspective of energy utilization. However, QD LEDs excited at 365 nm have unique advantages in eliminating the original peaks from the LED chip. Moreover, the green or red light excited by ultraviolet light has an advantage in colorimetry. Even for the 455 nm LED with the highest QD concentration at 7.0 wt%, the color quality could not compete with the 365 nm LED with the lowest QD concentration at 0.2 wt%. A 117.5% (NTSC1953) color gamut could be obtained by the 365 nm-excited RGB system, which is 32.6% higher than by the 455 nm-excited solution, and this can help expand the color gamut of LED devices. Consequently, this study provides an understanding of the properties of QD-converted LEDs under different wavelength excitations, and offers a general guide to selecting a pumping source for QDs.
White light-emitting diodes (WLEDs) based on quantum dots (QDs) are gaining increasing attention due to their excellent color quality. QDs films with planar structure are universally applied in WLEDs ...for color conversion, while they still face great challenges in high light extraction and thermal stability. In this study, a QDs film with a spherical shell structure was proposed to improve the optical and thermal performance for WLEDs. Compared with the conventional planar structure, the luminous efficacy of the QDs spherical shell structure is improved by 12.9% due to the reduced total reflection effect, and the angular-dependent correlated color temperature deviation is decreased from 2642 to 283 K. Moreover, the highest temperature of the WLED using a QDs spherical shell is 4.8 °C lower than that of the conventional WLED with a planar structure, which is mainly attributed to larger heat dissipation area and separated heat source. Consequently, this QDs spherical shell structure demonstrates superior performance of QDs films for WLEDs 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.
•An ultra-thin vapor chamber is developed with a thickness of only 0.5 mm.•Three kinds of capillary wick structures were prepared and compared.•The composite wick has excellent anti-gravity ...performance.•The maximum critical power of novel UTVC can be up to 60 W.•The UTVC has great potential for heat dissipation in portable electronic devices.
With the development of integrated and ultra-thin portable electronics, the ultimate heat dissipation power in extremely narrow spaces (<1 mm) is increasing year by year. However, the current critical power of ultra-thin vapor chamber (UTVC) is still at a low level, which hinders the development of high-power portable electronic products. In this study, novel UTVCs with a thickness of only 0.5 mm are prepared by utilizing the composite capillary wick. Different from the traditional multi-layer 2D copper mesh wick, the composite (CA/CB) wick is composed of multi-layer 2D copper mesh and 3D spiral woven mesh. UTVCs prepared from three different wicks, referred as to 2D-UTVC, CA-UTVC, CB-UTVC, were compared. Under different working conditions, the CA/CB-UTVC has better heat transfer performance than 2D-UTVC. In the horizontal state, the maximum effective thermal conductivity (Keff) of CA-UTVC and CB-UTVC is significantly improved by 86.8% and 60.2% compared to that of reference 2D-UTVC. The CA design is recommended for low heating power within 40 W, while the CB design is the optimal choice for high heating power above 40 W. The maximum critical power of CB-UTVC is up to 60 W with gravity support. Even at 50 W under anti-gravity condition, the thermal conductivity of CB-UTVC is still up to 11817.1 W/(m K), which is 29.5 times that of copper. The improved heat dissipation is due to the enhanced capillary force of the composite wick. This positive effect is facilitated by the combination of multiple 3D spiral woven meshes in the CB design. The optimized UTVC effectively reduces the maximum temperature by 14.3 °C compared to copper sheet under natural convection at 10 W heating power. The novel UTVC could provide a guarantee for the heat dissipation of high-power integrated portable electronic devices in the future.
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