Although silicone technology has existed for over 5 decades, this unique material continues to find usage in new
applications. Its unique chemical and physical characteristics allow its usage as fuel resistant gaskets, biologically
compatible for us in medical devices in the body, coatings for Atomic Oxygen protection in space, and for interocular
lenses for cataract disease. This paper will examine various silicones as effective encapsulants and lenses for High
Brightness LEDs (HB LEDs). Physical and optical characteristics will be tested to determine which materials may prove
to be the best.
Opto-electronic devices such as LEDs, optical sensors, LCDs and color filters have the need for optically
transparent encapsulants or adhesives. Maintaining the highest transmission possible of the
encapsulant/adhesive throughout the life of the device is a critical criteria for the device designer. Silicones
as encapsulants/adhesives in opto-electronic devices have been used throughout the last decade1, 2. The high
light flux and associated heat proved too much for the traditional epoxies. Data confirms silicone
encapsulants/adhesives provide longer optical transmission life than epoxy encapsulants3.
Almost all optical devices have some interaction with UV wavelengths. Manufacturers of Blue LEDs with
wavelengths near 405nm, and other LEDs that emit wavelengths deeper into the UV (365-399nm), have
concerns about the effects of this radiation on the light transmission of the encapsulant over time. LCD and
sensor devices may have UV radiation from the sun to contend with. This paper looks at many different
encapsulants/adhesives, silicone, epoxy and acrylate, for their change in optical transmission due to a 680-68000J/cm2 dose of radiation with the following spectral output: 34% in the UVA (320-399nm), 17% in the
UVB (280-319nm), and 49% concentrated at 405nm and 450nm. All samples were prepped and exposed
the same way so that comparisons between the samples would be meaningful. Results show that silicones
perform better than acrylates, which perform better than epoxies, and not all silicones perform equally.
Data will be provided of the best performing materials and a discussion of future work given the
understanding of the chemistry.
The optics industry widely uses silcones for various fiber optic cable potting applications and light emitting diode protection. Optics manufacturers know traditional silicone elastomers, gels, thixotropic gels, and fluids not only perform extremely well in high temperature applications, but also offer refractive index matching so that silicones can transmit light with admirable efficiency. However, because environmental conditions may affect a material's performance over time, one must also consider the conditions the device operates in to ensure long-term reliability. External environments may include exposure to a combination of UV light and temperature, while other environments may expose devices to hydrocarbon based fuels. This paper will delve into the chemistry of silicones and functional groups that lend themselves to properties such as temperature, fuel, and radiation resistance to show shy silicone is the material of choice for optic applications under normally harmful forms of exposure. Data will be presented to examine silicone's performance in these environment.