Fluorescence and Lasing in Dye-doped and Conjugated Polymer Microspheres

Abstract

This thesis explores the optical and microstructural properties of fluorescent and lasing polymer microspheres, as well as methods for their fabrication and size control. I investigate the fluorescent and lasing behaviour of polymer-coated glass microspheres by a combination of evanescent coupling, and fluorescence and lasing measurements. Coated glass microspheres lack perfect spherical symmetry and have a dense forest of resonances such that lasing preferentially occurs where these modes are most densely spaced within the gain band of the lasing medium. Next, I discuss the benefits of conjugated polymers (CPs) over dye-doped polymers before demonstrating a fabrication method which produces large CP microspheres (up to 50 times larger than those produced by other methods) and which are 20 times brighter than conventional dye-doped microspheres. Finally I develop a simple microfluidics fabrication method which enables good size control, from which arrays of monodisperse microspheres were synthesised from three different CPs (red, green and blue emitters, i.e., across the visible spectrum). The molecular weight of the CP as well as the choice of solvent and surfactant are shown to be important parameters in obtaining large (>5 microns) and relatively well formed microspheres. Conjugated polymer microspheres will be shown to have several advantages over conventional dye-doped particles for applications requiring a high emission intensity.