Patterned block-copolymer-silica mesostructures as host media for the laser dye rhodamine 6G

Rhodamine 6G-doped mesostructured silica is prepared by an acidic sol-gel r oute using poly-b-poly(propylene oxide)-b-poly(ethylene oxide) (EOx-POy-EOx ) block copolymer surfactants. Using low-refractive-index (n similar to 1.2 ) mesoporous SiO2 as a support, the synthesis is combined with soft lithogr aphy to produce high-quality waveguides. This enables efficient waveguiding in the line-patterned rhodamine 6G-doped mesostructured domains, which hav e a higher refractive index than both the mesoporous support and cladding. For the structure-directing block copolymer surfactants used, (EO)(20)(PO)( 70)(EO)(20) (P123) and (EO)(106)(PO)(70)(EO)(106)(F127), X-ray diffraction patterns and transmission electron microscopy reveal hexagonal mesophases, whose longitudinal cylinder axes are aligned predominantly parallel to the substrate plane. For samples made by micromolding-in-capillaries (MIMIC), t he longitudinal axes are also aligned along the longitudinal waveguide axes . Samples made by micromolding also possess a high mesostructural order, th ough in the absence of an aligning flow field, their long-range order (ca. several hundred nanometers) is lower than for samples processed using the M IMIC technique. When optically pumped, the rhodamine 6G-doped waveguides ex hibit amplified spontaneous emission with thresholds as low as similar to6 kW cm(-2), substantially lower than rhodamine 6G-doped sol-gel glasses. Thi s is attributed to the ability of the polymeric surfactant to coassemble wi th the dye molecules, thereby leading to high dye dispersions and reduced d ye dimerization. Additionally, rhodamine 6G shows good photostability in th e mesostructured waveguides, similar to that of rhodamine 6G in organically modified silicates.