As reducing energy consumption and encouraging low-carbon green growth becomes an issue globally, attention on light-emitting diodes (LEDs) has been increasing due to their low power consumption and high efficiency, resulting in the more economical use of electric power. In the past, LEDs were used as information display elements because of their fast response and long lifetime. But nowadays, the usage of LEDs is expanding. They are now being used as backlights and displays for LCD TVs and head lamps for cars. They are even expected to become the next-generation lighting products, replacing fluorescent lamps and other products.

Glassen capsulants seem to be better candidates than epoxy resin or silicon because they do not degrade the luminous intensity and they have high thermal and chemical stability. The phosphor-in-glass (PIG) type of encapsulant is fabricated by blending phosphor and glass frit. The requirements for these LED encapsulants are a low glass transition temperature in order to prevent a reaction between the glass and the phosphor and a low coefficient of thermal expansion in order to prevent cracks of the PIG.

The light-extraction efficiency in LED packaging can be enhanced by matching the refractive index between the phosphor and the encapsulant such that the scattering effect is minimized. In addition, the luminous efficiency of the LED packaging can be increased by optimizing the pores properties of the glass plate and the interfacial characteristics between the glass and the phosphor.