Jin-Kai Chang

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.

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.

Thermal-Stability Comparison of Glass- and Silicone-Based High-Power Phosphor-Converted White-Light-Emitting Diodes Under Thermal Aging

The lumen degradation, chromaticity shift, transmittance loss, and mean-time-to-failure (MTTF) evaluation in glass- and silicone-based high-power phosphor-converted white-light-emitting diodes (LEDs) (PC-WLEDs) under accelerated thermal aging at 150 °C, 200 °C, and 250 °C are presented and compared. The silicone-based PC-WLEDs exhibited less thermal stability than the glass-based PC-WLEDs by 1.86, 2.79, and 4.76 times higher lumen losses, 3.05, 3.26, and 6.84 times larger chromaticity shifts, and 1.82, 2.62, and 6.67 times greater transmittance losses at 150 °C, 200 °C, and 250 °C, respectively. The results also showed that the glass-based PC-WLEDs exhibited higher MTTF than the silicone-based PC-WLEDs by 20 times at room temperature. The peaks of the emission and excitation spectra for both silicone and glass phosphors were not significantly changed after thermal aging, evidenced by fluorescence spectrophotometer analyses. This indicated that the fluorescent ability of Ce:YAG-doped phosphor materials did not change after thermal aging and the transmittance loss was corresponding to the lumen loss and chromaticity shift. The results of the lumen loss, chromaticity shift, transmittance loss, and MTTF investigations clearly demonstrated that the thermal-stability performance of the glass-based PC-WLEDs was better than that of the silicone-based PC-WLEDs. The advantage of employing doped glass encapsulation in high-power PC-WLEDs could be explained: The material property of glass transition temperature of 750 °C was higher than that of silicone transition temperature of 150 °C. A better thermal stability phosphor layer of glass as encapsulation material may be beneficial to many applications where the LED modules with high power and high reliability are demanded for use in next-generation solid-state lighting.

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

Fabrication of low-temperature Ce 3+ :YAG doped glass for phosphor-converted white-light-emitting diodes

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

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.

Blue and white light emitting high power density LED modules

The optical characteristics of LTCeYDG applied to high-power PCWLEDs are demonstrated. The LTG powder exhibited a lower transition temperature about 567°C. The 4-wt% LTCeYDG, distribution uniformity and quantum efficiency were measured 85% and 34.5%, respectively.

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

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.

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

We present optical measurements of an optimized LED module consisting of 98 blue light emitting LED chips silver-sintered onto an aluminum nitride ceramic substrate within an area of 211 mm2. The module is cooled by a high performance microstructured water cooler. Using this cooler a maximum optical power density of 111.6 W/cm2 at a forward current of 3003 mA and 1255.6 W electrical input power could be achieved. Placing sintered glass discs doped with yellow phosphor in different concentrations in front of the module, white light with correlated color temperatures between 3600 K and 4200 K was produced.

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.