Novel materials for bottom-up 3-dimensionally structured organic lasers

  • Neue Materialien für bottom-up 3-dimensional strukturierte organische Laser

Mikosch, Annabel; Möller, Martin (Thesis advisor); Kühne, Alexander J. C. (Thesis advisor)

Aachen (2019)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2019

Abstract

This doctoral thesis investigates the application of π-conjugated polymer particles in organic micro lasers. A co-assembly of monodisperse particles in a curing silicate matrix is developed as an enabling technology to produce highly ordered, three-dimensional periodic structures, so-called photonic crystals. Photonic crystals diffract and slow light within the visible spectrum; the spectral range over which the crystal acts is called the optical band gap or stop band. The characteristic wavelength of this stop band can be adjusted by varying the particle size and refractive index contrast between particles and their surrounding medium. This work investigates particles completely composed of conjugated polymers, which therefore can be used as an active laser medium. In this way, the particles in their orderly arrangement form the amplifier medium as well as the resonator. This allows fast and simple production of an organic laser, avoiding the need for complicated and expensive nano structuring techniques. The suitability of such coassembled structures as micro lasers is investigated by means of short pulse laser spectroscopy. Coassembly is successfully achieved in an industrially relevant ink-jet printing process that enables self-assembled micro lasers to be processed and dublicated in a simple process. The potential for structured printing is demonstrated via the preparation of a readable QR code. Since such QR codes exhibit fluorescence, iridescence and laser emission in addition to their structure, these patterns could act as very effective counterfeiting security features. The functionality of the co-assembled structures can be increased by exchanging the dielectric silicate matrix with a semiconducting methylammonium lead halide perovskite matrix. The new semiconducting matrix is suitable for coassembly, since these perovskites are processable from orthogonal solvents. Thus, the polymer particles can also be processed in these solvents without losing their shape. In addition, the fluorescence of the perovskite matrix can be adjusted via the halide ratio over the entire visible spectrum. This tunability allows the production of an organic-inorganic hybrid material, in which the emission spectrum of the inorganic matrix overlaps with the absorption spectrum of the organic particles. This spectral alignment enables a radiation-free energy transfer that generates laser emission from the organic particles even though only the matrix is optically excited. These coassemblies exhibit random lasing at remarkably low laser thresholds. Thus, a new approach to manufacturing organic lasers is demonstrated bringing new insights towards achieving electrically-excitedorganic lasers.

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