Photonic Crystal Phosphors

Abstract

Photonic crystals (PCs) are photonic structures with periodically arranged index profiles. The periodicity of the PC results in a complex photonic band structure that may include a photonic band-gap (PBG), as a photonic counterpart of electronic energy band-gap under the periodic potential of a crystalline solid. Within the PBG wavelength range, light is prohibited to propagate through the PC structure. Meanwhile, photonic band-edge (PBE) modes possess many novel and unique properties. Group velocity of light with a PBE wavelength approaches zero, which makes its interaction with matter significantly stronger. In phosphor materials, a wavelength conversion of light occurs; they absorb energy of pump photons and re-radiate photons typically at a longer wavelength. Such color-conversion phosphors have many important applications in the general lighting industry. The phosphor-capped white light-emitting devices using light-emitting diodes (LEDs) or laser diodes (LDs) as pumping sources are recent characteristic examples of next-generation light sources for solid-state lighting. Consequently, considerable efforts have been devoted to improve the luminous efficiency of phosphors. However, most developmental works for highly efficient phosphors have focused on material aspects, such as the synthesis and adoption of new chemicals, which improve the internal quantum efficiency (IQE) of phosphor materials. In this thesis, I suggested a new concept of PC phosphors to enhance pumping efficiency for phosphor materials. Unlike any other methods for improvement of the IQE of phosphors or the extraction efficiency of emitted light from phosphors, I paid attention to the structural aspects of phosphors and increased concentration of pump photons in the structured phosphor media. More specifically, the electric field of the PBE modes is localized in the PC phosphors, which induces strong interaction between pump photons and phosphor materials. As directions of periodicity, such as vertical and lateral, two types of the PC phosphors were demonstrated in this thesis.