In order to avoid the Blue-ray LED lights and phosphor technology patent of Nichia, many LED manufacturers involved into researches of other White-ray emitting LED technologies. Currently, UV LED is the most anticipated technology among all. But it has two fatal defects: light leakage and low brightness, which will be hard to overcome in the short-term. Scientists was striving to solve these problems and meanwhile looking for other effective solutions to send out White-rays.
In 1987, two scientists from different country Eli Yablonovith and Sajeev John find the breakthrough almost at the same time. Theoretically, they found out that the periodical propagation state of electromagnetic waves in dielectric materials had band structures. They used two or more materials (with different refraction coefficients/dielectric constants) to compose the substance that contained photonic bands. The Photonic Crystal technology has been exiting for 20 years. Nowadays, it is the one of the most important core technologies which is highly concerned. This technology can be used in many other industries beside the LED lighting industry. Using second order photonic crystals to achieve White-rays was proved feasible. LED photonic crystal technology has become the focus of public attention and expected to be an effective method to get rid of the Nichia’s patent problem.
In following sections, we will discuss about the general construction of photonic crystals. Photonic crystals may have different periodic structures with different wavelengths, can be developed into first order crystals, second order crystals and third order crystals. Among these structures it is third order photonic crystals that have the most useful functions and can be used in various areas. But the manufacturing and commercialization of third order photonic crystals are almost impossible according to the current technology. Thus, instead of third order photonic crystals, it is second order crystals that are widely used in many industries, including LED lighting industry. The current LED photonic crystal technology is actually based on second order crystals working principles.
Generally, normal materials have fixed constructions, so these materials have a certain level of refractive coefficients. When electromagnetic waves travelled through these media, the wave number and frequency of these waves will impact the original refractive coefficients. Since photonic crystals have periodic structures, thus when light went through them, there must be multiple refractions.