In this paper, we present our investigation into the prevention of blue-light leakage in phosphor-converted white LEDs through a passive approach. Our study primarily focuses on the application and optimization of a specific thermochromic material known as Crystal Nano Cellulose (CNC). We integrated CNC within the epoxy lens of white LEDs. Importantly, under normal operating conditions, CNC minimally affects the optical properties of the emitted white light. However, in instances of overheating where blue-light leakage occurs, the temperature rise induces a darkening effect in CNC. By incorporating CNC as a responsive material in the design of white LEDs, our study offers a practical and efficient solution to address the adverse effects of blue-light leakage resulting from overheating. This enhancement not only improves the safety and comfort for users but also serves as an early warning mechanism for the aging of phosphor-converted white LEDs.
In the present work, a purple laser diode of 405 nm is employed for the excitation of different types of phosphors for the purpose of building a white light source. Three different types of phosphor materials were synthesized – a blue phosphor (BAM), a green phosphor (GYAG) and a red phosphor based on nitride. These samples were synthesized in the form of silicone pellets, having different thicknesses and different concentrations in the silicone matrix. In this study, two different approaches were followed. First, the three different samples were stacked together in various combinations to study the colorimetric parameters of the emitted converted light, particularly the correlated color temperature (CCT) and the color rendering index (CRI). In the second approach, the three types of phosphors were merged in the same silicone pellet. Pellets with different thickness and ratio of the three phosphors were prepared, and their CCT and CRI parameters were measured under laser excitation. In the first case, a CCT of 2264 K and a CRI of 74 were achieved while with the second approach, an average temperature of 4500 K and a CRI of 85 were reached. While the difference between the CRI values for both cases is not big, the CCT value of the mixed samples is twice as high as the value of the stacked pellets, something attributed to simultaneous excitation of phosphors in mixed samples while, when stacked, each material is irradiated in a specific order.
The phosphor excitation by blue laser diode and an influence of its irradiation on the material were investigated. Two types of materials were elaborated to perform these experiments—yellow phosphor (YAG) and green phosphor mixed with nitride phosphor (GYAG). These phosphors were packaged into silicone plates, having different thickness and concentration in silicon resin. The results from exciting the phosphor by blue laser present that emission of converted light increases when concentration and thickness increase. Also, the dependency of these two parameters on optical power shows certain behavior. Subsequently, the concentration and thickness were replaced by particle number in sample. It revealed that the dependency of the particle numbers on the optical power can replace the conventional parameters as thickness or concentration. Results show that correlated color temperature finds it dependency on number of particles also. In addition, it turned out, that for each of the material, there might exist an optimal particle number for the maximum luminous power. Finally, the influence of the irradiation of blue laser diode on the materials was investigated. After intensive irradiation for 30 min, we observed that the efficiency of light conversion decreases. It can be caused by damages made by laser on particles. Results show parts of nitride (650 nm) conversion decrease less than yellow or green phosphor. Less affection of irradiation can be explained by nitride being very covalent material, more resistant to modification. Also, we found that there is no fundamental modification of material structure because of no changing in spectrum shape of converted light.
The phosphor excitation by blue laser diode and an influence of its irradiation on the material were investigated. Two types of materials were elaborated to perform these experiments – yellow phosphor (YAG) and green phosphor mixed with nitride phosphor (GYAG). These phosphors were packaged into silicone plates, having different thickness and concentration in silicon resin. The results from exciting the phosphor by blue laser present that emission of converted light increases when concentration and thickness increases. Also the dependency of these two parameters on optical power shows certain behavior. Subsequently, the concentration and thickness was replaced by particle number in sample. It revealed that the dependency of the particle numbers on the optical power can replace the conventional parameters as thickness or concentration. Results show that correlated color temperature finds it dependency on number of particles also. In addition, it turned out, that for each of the material, there might exist an optimal particle number for the maximum luminous power. Finally, the influence of the irradiation of blue laser diode on the materials was investigated. After intensive irradiation for 30 minutes, we observed efficiency of light conversion decreases. It can be caused by damages made by laser on particles. Results show parts of nitride (650nm) conversion decrease less than yellow or green phosphor. Less affection of irradiation can be explained by nitride being very covalent material, more resistant to modification. Also, we found that there is no fundamental modification of material structure because of no changing in spectrum shape of converted light.
We performed the simulation and experiment to investigate the influence of Zirconium dioxide (Zirconia, ZrO2) particles on the optical properties of phosphor converted white LED (pcW-LED). An efficient optical model was developed and applied to the incorporation diffuse particle of ZrO2 into a hemisphere package containing YAG phosphors. The optical properties (chromaticity, packaging efficiency) were estimated as a function of phosphor and ZrO2 particles, through the calculation of effective radius, refractive index, and absorption and conversion efficiency, in a range of correlated color temperature 4500 K to 6500 K. In the same way, the amount of phosphor and ZrO2 can be calculated accurately to obtain a targeted optical property in a hemisphere LED design. Especially, the angular distribution of CCT was also diminished, and even almost inexistent for low CCT design. In addition, the adding of ZrO2 particles allows clearly decreasing the amount of phosphor for an identical target CCT. It is really suitable in the context of decreasing the amount of phosphor or in some applications where the color uniformity is an important parameter, like indoor down-lighting.
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