Heat and fluid flow in high-power LED packaging and applications

Colloidal quantum-dot light-emitting diodes (QDLEDs) with the HfO2/SiO2-distributed Bragg reflector (DBR) structure are fabricated using a pulsed spray coating method. Pixelated RGB arrays, 2-in. wafer-scale white light emission, and an integrated small footprint white light device are demonstrated. The experimental results show that the intensity of red, green, and blue (RGB) emission exhibited considerable enhancement because of the high reflectivity in the UV region by the DBR structure, which subsequently increases the use in the UV optical pumping of RGB QDs. A pulsed spray coating method is crucial in providing uniform RGB layers, and the polydimethylsiloxane (PDMS) film is used as the interface layer between each RGB color to avoid cross-contamination and self-assembly of QDs. Furthermore, the chromaticity coordinates of QDLEDs with the DBR structure remain constant under various pumping powers in the large area sample, whereas a larger shift toward high color temperatures is observed in the integrated device. The resulting color gamut of the proposed QDLEDs covers an area 1.2 times larger than that of the NTSC standard, which is favorable for the next generation of high-quality display technology.

https://ir.nctu.edu.tw:443/bitstream/11536/20821/1/000312301800008.pdf

Resonant‐Enhanced Full‐Color Emission of Quantum‐Dot‐Based Display Technology Using a Pulsed Spray Method

Visible Light Communication (VLC) as a new technology for ultrahigh-speed communication is still limited when using slow modulation light-emitting diode (LED). Alternatively, we present a 4-Gbit/s VLC system using coherent blue-laser diode (LD) via 16-quadrature amplitude modulation orthogonal frequency division multiplexing. By changing the composition and the optical-configuration of a remote phosphor-film the generated white light is tuned from cool day to neutral, and the bit error rate is optimized from 1.9 × 10(-2) to 2.8 × 10(-5) in a blue filter-free link due to enhanced blue light transmission in forward direction. Briefly, blue-LD is an alternative to LED for generating white light and boosting the data rate of VLC.

https://nanoenergy.kaust.edu.sa/Documents/4-Gbits%20visible.pdf

4-Gbit/s visible light communication link based on 16-QAM OFDM transmission over remote phosphor-film converted white light by using blue laser diode

A simple and practical method for preparing phosphor glass is proposed. Phosphor distribution and element analysis are investigated by optical microscope and field emission scanning electron microscope (FE-SEM). The phosphor particles dispersed in the matrix are vividly observed, and their distributions are uniform. Spectrum distribution and color coordinates dependent on the thickness of the screen-printed phosphor layer coupled with a blue light emitting diode (LED) chip are studied. The luminous efficacy of the 75 μm printed phosphor-layer phosphor glass packaged white LED is 81.24 lm/W at 350 mA. This study opens up many possibilities for applications using the phosphor glass on a selected chip in which emission is well absorbed by all phosphors. The screen-printing technique also offers possibilities for the design and engineering of complex phosphor layers on glass substrates. Phosphor screen-printing technology allows the realization of high stability and thermal conductivity for the phosphor layer. This phosphor glass method provides many possibilities for LED packing, including thin-film flip chip and remote phosphor technology.

Preparation of a YAG:Ce phosphor glass by screen-printing technology and its application in LED packaging

A glass phosphor layer with ultra-high thermal stability appropriate for phosphor-converted white light-emitting diodes (PC-WLEDs) is demonstrated. The results showed PC-WLEDs utilizing the high thermal stable glass phosphor maintained good thermal stability in lumen, chromaticity, and transmittance characteristics under the thermal aging condition up to 350 $^{\circ}{\hbox{C}}$ . This is a considerable high operating temperature for a phosphor layer in the PC-WLEDs. The lumen degradation, chromaticity shift, and transmittance loss in the glass-based PC-WLEDs under thermal aging at 150 $^{\circ}{\hbox{C}}$ , 250 $^{\circ}{\hbox{C}}$ , 350 $^{\circ}{\hbox{C}}$ , and 450 $^{\circ}{\hbox{C}}$ are also presented and compared with those of silicone-based PC-WLEDs under thermal aging at 150 $^{\circ}{\hbox{C}}$ and 250 $^{\circ}{\hbox{C}}$ . The result clearly demonstrated that the glass-based PC-WLEDs exhibited better thermal stability in lumen degradation, chromaticity shift, and transmittance loss than the silicone-based PC-WLEDs. The advantages of glass encapsulation in high-temperature operation of the PC-WLEDs could be explained that the glass transition temperature of the glass phosphor (567 $ ^{\circ}{\hbox{C}}$ ) was much higher than it of silicone (150 $ ^{\circ}{\hbox{C}}$ ). The newly developed ultra-high thermal-stable glass is essentially critical to the application of LED modules in the area where the high-power, high-temperature and absolute reliability are required for use in the next-generation solid-state lighting.

Ultra-High Thermal-Stable Glass Phosphor Layer for Phosphor-Converted White Light-Emitting Diodes

High efficiency white light-emitting diodes with superior color-mixing have been investigated. It is suggested that the patterned remote phosphor structure could improve the uniformity of angular-dependent correlated color temperature (CCT) and achieve high chromatic stability in wider operating current range, as compared to the conventional remote phosphor coating structure. In this experiment, we employed a pulse spray coating method to place the patterned phosphor on the package and to leave a window region. The window area, a clear space without coating of the phosphor not only increases the extraction efficiency of blue rays at large angle, but also improves the stability of angular-dependent CCT. Moreover, the CCT deviation could be reduced from 1320 K to 266 K by this patterned remote phosphor method, and the stray blue/yellow light within the package can be effectively reduced and controlled. The design was verified both experimentally and theoretically.

https://ir.nctu.edu.tw:443/bitstream/11536/21714/1/3a91b922e430e2d0f0759a4707798bb5.pdf

Patterned structure of REMOTE PHOSPHOR for phosphor-converted white LEDs

We have successfully demonstrated the enhanced luminous flux and lumen efficiency in white light-emitting diodes by the randomly textured phosphor structure. The textured phosphor structure was fabricated by a simple imprinting technique, which does not need an expensive dry-etching machine or a complex patterned definition. The textured phosphor structure increases luminous flux by 5.4% and 2.5% at a driving current of 120 mA, compared with the flat phosphor and half-spherical lens structures, respectively. The increment was due to the scattering of textured surface and also the phosphor particles, leading to the enhancement of utilization efficiency of blue light. Furthermore, the textured phosphor structure has a larger view angle at the full width at half maximum (87°) than the reference LEDs.

/pdf/a-novel-randomly-textured-phosphor-structure-for-highly-532ol8khp8.pdf

A novel randomly textured phosphor structure for highly efficient white light-emitting diodes

https://ir.nctu.edu.tw:443/bitstream/11536/16545/1/000304689500025.pdf

Improvement of lumen efficiency in white light-emitting diodes with air-gap embedded package

White light-emitting diodes with air-gap embedded package were proposed and fabricated through a simple method including pulsed spray coating. The lumen efficiency of air-gap embedded LED was enhanced by 8.8% compared to reference remote-phosphor LED.

Improving the lumen efficiency by air-gap embedded package in white light-emitting diodes

White light-emitting diodes (LEDs) with roughened-dispensing package through a simple imprinting technique are demonstrated and fabricated. The imprinting mold was fabricated by naturally wet-etched (100) Si substrate, which did not require expensive lens mold and pattern definition. The lumen output of roughened-dispensing package was enhanced by 5.4 % and 2.5 %, at driving current of 120 mA, compared to reference flat phosphor-dispensing package without and with lens molding, respectively.

C. C. Yeh

Papers

Patterned structure of REMOTE PHOSPHOR for phosphor-converted white LEDs

A novel randomly textured phosphor structure for highly efficient white light-emitting diodes

Improvement of lumen efficiency in white light-emitting diodes with air-gap embedded package

Improving the lumen efficiency by air-gap embedded package in white light-emitting diodes

Improvement of lumen efficiency in white light-emitting diodes by roughened-dispensing package