Investigation of Low Lasing Threshold Organic Semiconductors and their Integration into Planar and Defect Microcavities

Claronino, Peter

Abstract

This thesis presents a study into organic semiconductor laser materials and the design and fabrication of distributed Bragg reflector microcavities that can achieve low threshold lasing. A range of organic laser materials were investigated, where the molecular packing for each material was probed using X-ray scattering to understand the effect on the amplified spontaneous emission (ASE) threshold. It was found that increasing the concentration of a fluorescent dye (Fluorescent Orange) dispersed in an inert polystyrene matrix caused aggregation. This was observed by an increase in the molecular disorder and quenching, and at high concentrations, supressed ASE. The lowest threshold measured in solution processed Fluorescent Orange was 259 μJ cm-2. This threshold was reduced to 55 μJ cm-2 by using co-thermal evaporation with BCP. The ASE for the copolymer BN-PFO was also explored where increasing the relative fraction of BN to PFO resulted in the increase in molecular disorder. This enhanced disorder led to a reduction in the ASE threshold to 19 μJ cm-2. Finally, the lowest threshold (13.8 μJ cm-2) measured was from the small molecule, BSBCz. The two lowest ASE threshold materials (BN-PFO 12.7% and BSBCz) were then integrated within planar microcavities to achieve low-threshold lasing (12 μJ cm-2 and 1.7 μJ cm-2). This resulted in the lowest lasing threshold reported for a polymer microcavity. This record lasing threshold was reduced further by adding lateral confinement using laser patterning to write defects into the microcavity. This additional confinement resulted in a reduction in the lasing threshold from 11 μJ cm-2 to 7 μJ cm-2. This laser patterning approach offers a quick and simple way to fabricate micro-scale organic lasers that have improved lasing thresholds and a four times enhancement in the Q factor.

Citation

Claronino, P. (2024). Investigation of Low Lasing Threshold Organic Semiconductors and their Integration into Planar and Defect Microcavities. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/5001507

• Thesis Type: Thesis
• Deposit Date: Jan 6, 2025
• Publicly Available Date: Jan 13, 2025
• Keywords: Physics
• Public URL: https://hull-repository.worktribe.com/output/5001507
• Award Date: Jun 4, 2024