Phosphor in Glass（PiG）
A new product from Nakamura Yuji
Visualization of illumination process of traditional resin phosphor
Normal white LEDs use red and green phosphor mixing with silicone, epoxy or other resins. The mixture is cast onto the chip to convert the blue light emitted from the chip into red and green light. Although this approach is simple to prepare, it has some defects like, resin is susceptible to heat and water and the nonuniformity distribution of phosphor particles affects the chromaticity of output light.
Visualization of illumination process of PiG
PiG on the other hand, is a solid plate, which can be cut to fit the shape of LED chip perfectly. In addition, the phosphor particles are dispersed more homogenously in the glass than resin and thus the chromaticity and spatial distribution of the converted light are near to perfect. The glass is also more stable than resin to protect phosphor from the damage of heat and water vapor.
Features
High Luminance density
Thermal conductivity of PiG is normally 1 – 20 W/(K·m) compared to that of resin is generally < 0.2 W/(K·m). Larger Thermal conductivity and better thermal stability contribute to the endurance of high luminance density of PiG as a result of the ability to conduct heat away and reduce the temperature. The luminance density of PiG could reach 1000 lm/mm^2 and above, in contrast of that resin can bear less than 200 lm/mm^2.
Homogenous Illumination
The area of traditional silicone phosphor is larger than the surface of the chip (or diode). This mismatch causes yellow spot at the around. However, PiG can be cut to any shape and thus can fit the chip perfectly, which solves the problem.
Consistent Chromaticity
The homogenous distribution of the phosphor particles in PiG results in the more concentrated chromaticity coordinates and thus the color of the emission light is more accurate. The color deviation is small enough for omitting the binning process.
Long Lifespan
PiG is stable under high temperature and high humidity. So it is more reliable either at working or storage condition and has a long life time. Our test shows that PiG has a much slower attenuation (< 4%) than silicon phosphor (~18%) after 1500h at an operation current of 1A.
