Li-Yin Chen

Novel broadband glass phosphors for high CRI WLEDs

New broadband glass phosphors with excellent thermal stability were proposed and experimentally demonstrated for white light-emitting-diodes (WLEDs). The novel glass phosphors were realized through dispersing multiple phosphors into SiO₂ based glass (SiO₂-Na₂O-Al₂O₃-CaO) at 680°C. Y₃Al₅O₁₂:Ce³⁺ (YAG), Lu₃Al₅O₁₂:Ce³⁺ (LuAG), and CaAlSiN₃: Eu²⁺ (nitride) phosphor crystals were chosen respectively as the yellow, green, and red emitters of the glass phosphors. The effect of sintering temperature on inter-diffusion reduction between phosphor crystals and amorphous SiO₂ in nitride-doped glass phosphors was studied and evidenced by the aid of high-resolution transmission electron microscopy (HRTEM). Broadband glass phosphors with high quantum-yield of 55.6% were thus successfully realized through the implementation of low sintering temperature. Proof-of-concept devices utilizing the novel broadband phosphors were developed to generate high-quality cool-white light with trisstimulus coordinates (x, y) = (0.358, 0.288), color-rending index (CRI) = 85, and correlated color temperature (CCT) = 3923K. The novel broadband glass phosphors with excellent thermal stability are essentially beneficial to the applications for next-generation solid-state indoor lighting, especially in the area where high power and absolute reliability are required.

High-performance glass phosphor for white-light-emitting diodes via reduction of Si-Ce 3+ :YAG inter-diffusion

A novel Ce3+:YAG doped sodium glass (CeYDG) with low-melting temperature of 693°C and high internal quantum yield of 68% for white-light-emitting diodes (WLEDs) is demonstrated. The glass phosphor possesses glass transition temperatures of 578°C which exhibits a better thermal stability to overcome the thermal limitation of conventional Ce3+:YAG doped silicone due to low thermal stability of around 150°C. To the best of authors’ knowledge, this is the highest quantum yield yet reported for thermally stable glass phosphors. The high quantum yield is achieved by lowering the sintering temperature of 700°C for glass phosphor, which substantially reduces Si-Ce3+:YAG inter-diffusion, evidenced by high-resolution transmission electron microscopy (HRTEM). This new CeYDG with high-quantum yield is essentially beneficial to the applications for next-generation solid-state lighting in the area where high power and absolute reliability are required and where silicone simply could not stand the heat or other deteriorating factors due to its low thermal stability.

Chromaticity tailorable glass-based phosphor-converted white light-emitting diodes with high color rendering index

In this paper, Lu3Al5O12:Ce3+ and CaAlSiN3: Eu2+ co-doped glass are presented as color conversion materials for white light-emitting diodes (WLEDs). Through adjusting the thickness of the glass phosphors, the chromaticity and CCT of the WLEDs follows the Planckian locus well. The WLEDs show CCT ranging from ~4000K to ~7000K with high CRI ranging from 83 to 90 due to the wide emission spectrum from the proposed glass phosphors. The glass phosphors provide an effective way to achieve chromaticity-tailorable WLEDs with high color quality for indoor lighting applications.

Optical Model for Novel Glass-Based Phosphor-Converted White Light-Emitting Diodes

We proposed an optical model for phosphor-converted white LEDs (pc-WLEDs) that utilized Ce:YAG doped glasses as novel phosphor-converted materials. In this model, precise simulation of the chromatic performance of the glass-based pc-WLEDs was conducted. Between optical simulation and experimental measurement, the color difference

High-thermal-stability white light-emitting-diodes employing broadband glass phosphor

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Optical inspection algorithm for dust defect of compact camera module

was 1.2%. Meanwhile, the difference of correlated color temperature limited from 1 wt% to 5 wt% phosphor concentration between the simulation and measurement was 184 K. Such a model for glass phosphors will be helpful to design high-power glass-based pc-WLEDs.

Next-generation high-reliability laser light engine by glass phosphor-converted layer(Conference Presentation)

We report the high-thermal-stability white light-emitting-diodes (WLEDs) employing broadband glass phosphors. The broadband glass phosphors were fabricated by sintering the mixture of multiple phosphors and SiO2-based glass (SiO2-Na2O-Al2O3-CaO) at 680℃. Y3Al5O12:Ce 3+ (YAG), Lu3Al5O12:Ce3+ (LuAG), and CaAlSiN3: Eu2+ (Nitride) phosphor crystals were chosen as the yellow, green, and red emitters of the glass phosphors, respectively. The results showed that the broadband phosphors exhibited high quantum-yield of 54% and color-rendering index (CRI) of 90. The lumen degradation, chromaticity shift, and transmittance loss in the broadband glass-based WLEDs under thermal aging temperature at 150, 250, 350 and 450℃ were also presented and compared with those of silicone-based WLEDs under thermal aging temperature at 150 and 250℃. The results demonstrated that the broadband glass-based WLEDs exhibited better thermal stability in lumen degradation, chromaticity shift, and transmittance loss than the silicone-based WLEDs. The excellent thermal stability of the broadband glass-based WLEDs with high CRI is essentially beneficial to the applications for next-generation solid-state indoor lighting, especially in the area where high power and absolute reliability are required.

Next-generation glass-base phosphor-converted laser light engine

Dust is one of the most critical issues in assembly of Compact Camera Module (CCM) for mobile phones. Defect due to dust entry or dust deposit severely degrades image quality. There have been lots of literatures about the compensating of dust defect on images by image processing, but the discussion about where the dust locates is still deficient. Dust may sneak in the CCM in any step of packaging process, so the analysis of the dust location may be useful for improving of the production line. This work develops an optical inspection algorithm to detect the location of dust inside CCM based on imaging optics. A planar light source with uniformly emission is designed as the capture target. A series of defocused images are then taken and analyzed. According to the dependence of the image defect on the capture distance, the location of the dust can be well defined. This inspection algorithm provides an easy and efficient way to help manufacturers improve their packaging process.

High-temperature (350°C) glass phosphor layer for converted white light-emitting diodes

A new scheme of high-reliability laser light engine (LLE) employing a novel glass-based phosphor-converted layer is proposed and demonstrated. The LLE module consists of a high-power blue light laser array and a color wheel, which includes two glass-based phosphor-converted layers of yellow Ce:YAG and green Ce:LuAG and a micro motor. The combinations of blue, yellow, and green lights produce high-purity phosphor-converted white-laser-diodes (PC-WLDs). The lumen degradation and chromaticity shift in the glass-based phosphor-converted layer under different laser powers are presented and compared with those of silicon-based PC-WLDs. The results showed that the glass based PC-WLDs exhibited in lower lumen loss and less chromaticity shifts than the silicon-based PC-WLDs. The long term reliability study evaluation in glass- and silicone-based PC-WLDs under high-power 120 W at room temperature for 20,000 hours is also presented and compared. The result showed that the silicone-based PC-WLDs exhibited 50% in lumen decay which failed in operation, while the glass-based PC-WLDs only exhibited 2% in lumen decay. This indicates that the proposed LLE modules are benefit to employ in the area where the silicone-based material fails to stand for long and strict reliability is highly required. This study demonstrates the advantages of adapting novel glass as a phosphor-converted color wheel in the LLE modules that provide unique high-reliability as well as better performance for use in the next-generation laser projector system.

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

A highly reliable laser light engine (LLE) employing a novel glass-based phosphor-converted layer is experimentally demonstrated. The LLE module consisted of a blue light laser array and a color wheel, which included two glass-based phosphor-converted layers of yellow YAG:Ce and green LuAG:Ce and a micro motor. The blue light laser array was used to excite the color wheel to create yellow and green lights. The combination of the blue, yellow, and green lights produced high-purity white light for use in LLEs. The glass-based LLE exhibited better thermal stability, higher luminous efficiency of 64.7lm/W(YAG:Ce) and 67.2lm/W (LuAG:Ce), and higher purity of 95.4%(YAG:Ce) and 77.4%(LuAG:Ce). This study clearly demonstrates the advantages of adapting novel glass as a phosphor-converted color wheel in LEL modules that provide higher reliability and better performance of laser projectors for use in the next generation LLEs, particularly in the area where the conventional LLEs employing silicone-based phosphor fails to stand for long and strict reliability is highly required.