Chun-Chin Tsai

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.

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

Lumen degradation and chromaticity shift in glass and silicone based high-power phosphor-converted white-emitting diodes under thermal tests

\Delta E

The study of LED light source illumination conditions for ideal algae cultivation

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.

The quality study of recycled glass phosphor waste for LED

The lumen degradation and chromaticity shift in glass and silicone based high-power phosphor-converted white-emitting diodes (PC-WLEDs) under accelerated thermal tests at 150°C, 200°C, and 250°C are presented and compared. The glass based PC-WLEDs exhibited better thermal stability than the silicone by 4.8 time reductions in lumen loss 6.8 time reductions in chromaticity shift at 250°C, respectively. The mean-time-to-failure (MTTF) evaluation of glass and silicone based high-power PC-WLEDs in accelerated thermal tests is also presented and compared. The results showed that the glass based PC-WLEDs exhibited higher MTTF than the silicone by 7.53 times in lumen loss and 14.4 times in chromaticity shift at 250°C, respectively. The thermal performance of lumen, chromaticity, and MTTF investigations demonstrated that the thermal stability of the glass based PC-WLEDs were better than the silicone. A better thermal stability phosphor layer of glass as encapsulation material may be beneficial to the many applications where the LED modules with high power and high reliability are demanded.

Packaging of phosphor-converted white light-emitting diodes for solid-state lighting

Utilizing LED light source modules with 3 different RGB colors, the illumination effect of different wavelengths had been investigated on the growth curve of the same kind of micro algae. It was found that the best micro algae culturing status came out with long wavelength light such as red light (650~670 nm). Based on the same condition for a period of 3 weeks , the grown micro algae population density ratio represented by Optical Density (O.D.) ratio is 1：0.4：0.7 corresponding to growth with Red, Green, Blue light sources, respectively. Mixing 3 types and 2 types of LEDs with different parameters, the grown micro algae population densities were compared in terms of O.D. Interestingly enough, different light sources resulted in significant discoloration on micro algae growth, appearing yellow, brown, green, etc. Our experiments results showed such discoloration effect is reversible. Based on the same lighting condition, micro algae growth can be also affected by incubator size, nutrition supply, and temperature variation. In recent years, micro algae related technologies have been international wise a hot topic of energy and environmental protection for research and development institutes, and big energy companies among those developed countries. There will be an economically prosperous future. From this study of LED lighting to ideal algae cultivation, it was found that such built system would be capable of optimizing artificial cultivation system, leading to economic benefits for its continuous development. Since global warming causing weather change, accompanying with reducing energy sources and agriculture growth shortage are all threatening human being survival.

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

To study the feasibility and quality of recycled glass phosphor waste for LED packaging, the experiments were conducted to compare optical characteristics between fresh color conversion layer and that made of recycled waste. The fresh color conversion layer was fabricated through sintering pristine mixture of Y.A.G. powder [yellow phosphor (Y3AlO12 : Ce3+). Those recycled waste glass phosphor re-melted to form Secondary Molten Glass Phosphor (S.M.G.P.). The experiments on such low melting temperature glass results showed that transmission rates of S.M.G.P. are 9% higher than those of first-sintered glass phosphor, corresponding to 1.25% greater average bubble size and 36% more bubble coverage area in S.M.G.P. In the recent years, high power LED modules and laser projectors have been requiring higher thermal stability by using glass phosphor materials for light mixing. Nevertheless, phosphor and related materials are too expensive to expand their markets. It seems a right trend and research goal that recycling such waste of high thermal stability and quality materials could be preferably one of feasible cost-down solutions. This technical approach could bring out brighter future for solid lighting and light source module industries.

High-color rendering indices performance of glass based phosphor-converted white light-emitting diodes for solid state lighting

For both high conversion efficiency and thermal stability, glass-based phosphor-converted white light-emitting diodes (GBPC-WLEDs) were packaged for optic characterization study. Fabricated by flip chip, glass based PC-WLEDs were found Tj dramatically decreased, and emission intensity eminently raised up. If driven by large electric current, such samples would have even lower Tj 36°C. These characteristics will significantly improve thermal stability and lifetime of the LED packaging modules. In addition to high optical quality and low manufacture cost, such better thermal stability of glass phosphor layer may be beneficial for public policy of mass replacement of street lights with solid-state lighting LED as one of many applications requiring high-power and high reliability.

Visual susceptibility analysis for solid-state lighting of commercial PC-WLEDs

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.

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

The high-temperature operation of glass based phosphor-converted warm-white light-emitting diodes (PC-WWLEDs) is demonstrated. The fabrication and characteristics of low-temperature phosphor (Yollow:Ce:3+:YAG, Greed:Tb3+:YAG, Red:CaAlClSiN3:Eu2+) doped glass applied to high color rendering indices warm-white-light-emitting diodes was presented. In this property is color coordinates (x, y) = (0.32, 0.28), quantum yield (QY) = 55%, color rending index (CRI) =85, correlated color temperature (CCT) =3900K. The result showed the PC-WLEDs maintained good thermal stability at the high temperature operation. The QY decay, CRI attenuation and chromaticity shift in glass and silicone based high-power PC-WLEDs under thermal aging at 150°C and 250°C are also presented and compared. The result indicated that the glass based PC-WLEDs exhibited better thermal stability than the silicone. And the color rendering indices (CRI) glass phosphor may have potential used as a phosphor layer for high-performance and low-cost PCWLEDs used in next-generation indoors solid-state lighting applications.