Low-Threshold Lasing in 3D Dye-Doped Photonic Crystals Derived from Colloidal Self-Assemblies

Abstract

In this article, we demonstrated low-threshold lasing in three-dimensional (3D) polymeric photonic crystals derived from colloidal suspensions. To achieve this, we used monodisperse silica beads in a photocurable refractive index matched medium with high viscosity and polarity. In this system, the colloidal silica beads rapidly self-organized into nonclose-packed fcc crystals because of strong repulsive interparticle potential relative to diminishing van der Waals attraction, and subsequently the colloid crystals were solidified by UV irradiation. Dye molecules as optical gain medium were incorporated in the polymeric matrix by simply mixing the dye molecules and the photocurable suspension before casting the photonic crystal films. The translucent composite photonic films showed emission inhibition and enhancement due to the low photon density of states (DOS) at the stop band and high DOS at the band edge, respectively. On the other hand, the porous photonic films, which were prepared by removal of silica particles from the composite films, exhibited larger bandwidth and higher reflectivity (>80%) due to the enhanced refractive index contrast. Under irradiation of excitation light source, the porous photonic film showed strongly enhanced stimulated emission at the band edge by a factor of more than 300 with respect to the spontaneous emission of dye molecules embedded in a bulk film without nanostructure. In addition, the lasing wavelength could be controlled by simply changing the particle volume fraction in the composite films from which the porous films were prepared. Moreover, the threshold excitation intensity was reduced by a factor of one-tenth relative to the previously reported values. The simple method for preparing 3D photonic crystals described here and subsequent lasing characteristics have great potential in a broad range of applications including displays, μ-TAS, and optofluidic light sources.