Manipulating photoluminescent properties via spatial control of optically active media within polymer matrices and templates

Abstract

Fundamentally, light management plays a central role in industries such as life science, health, communication, energy, and agriculture. Research involving further understanding and control of light to the benefit of humankind continues to be a driving force for advancing society. Of particular interest is furthering our understanding of light-matter interactions. By controlling these interactions, intriguing optical phenomenon such as directional light modulation and low threshold lasing can be achieved, particularly with photonic assemblies of gain medium. This study focuses on understanding the fundamental aspect of light-matter interactions and propagation in gain medium such as organic dyes, quantum dots (QD), and QD-polymer nanocomposites. Specific emphasis is placed on understanding the QD-polymer interface to realize guided assembly in nanocomposites and on finding the parameters governing optical coupling between nanocomposite structures with particular focus on photonic cavity size, shape, position, and obtaining dynamic tunability. This work provides a scientific framework which demonstrates useful methodologies for designing photonic systems that require control of light-matter interactions including emission, mode activity, and resonator coupling. Specifically, Cd based core and core/shell QDs with different interfacial architectures, including core/shell with sharp interface, and core/graded shell, are investigated to understand dynamic photoluminescence behavior. Core/shell QDs with a CdSe/ZnS composition showed the most dynamic PL behavior with an emission signature that showed semi-reversible recovery behavior based on exposure conditions. Next, an ultrafast crosslinking technique incorporating thiol-ene chemistry was used to realize QD-polymer nanocomposites with high loading, minimal aggregation and optical scattering, and tunable mechanical properties. Finally, lithographic techniques were used to fabricate high resolution templates for whispering gallery mode microsphere resonator assembly, and individual and coupled microdisk resonators with strong coupling. Taking advantage of 3D lithography, with ~200nm resolution, and unique system design we obtain microsphere resonators with sub-100nm gap spacing, equating to strong evanescently coupled resonators. The knowledge obtained herein can be used to aid in the design of robust optical materials with added functionality and tunability for sensing and enhanced light modulation leading to unique optical phenomenon such as directional lasing and unidirectional light propagation.