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.
