Elucidating exciton-polaritons in organic and two-dimensional metal halide semiconductors
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Quiros Cordero, Victoria
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Abstract
Exciton-polaritons combine properties of light (i.e., low effective mass, delocalization) and electron-hole pairs bound by Coulombic forces or excitons (i.e., many-body interactions), opening doors for light-based computing, long-range energy harvesting, and tunable chemical reactivity, to name a few of their applications. Polaritons emerge in semiconductors placed within optical microcavities when non-dissipative, coherent energy exchange between excitons and the microcavity optical modes (i.e., standing electromagnetic waves) dominates over the system's energy losses. This regime is also known as strong light-matter coupling.
This Ph.D. thesis overcomes challenges of exciton-polaritons in organics and two-dimensional metal halide semiconductors at two distinct fronts: the fabrication of photonic structures with strong light-matter coupling and the characterization of exciton-polariton photophysics. We enable polaritons in a wider variety of materials by developing non-destructive fully solution-processed microcavities, which offer the required electromagnetic field enhancements for strong light-matter coupling and are highly compatible with temperature-sensitive semiconductors. These microcavity structures are produced from solution at ambient conditions using common processing methods (i.e., dip coating) and comprise a high-refractive-index titanium oxide hydrate/poly(vinyl alcohol) hybrid material and low-refractive-index commodity polymers. On the other front, we identify nonlinear processes building up and hindering the population of exciton-polaritons in these material classes. We resolve nonlinear processes that are faster than the polariton lifetime (<< 1 ps) and comparable to the exciton lifetime (>> 1 ps) by utilizing excitation correlation photoluminescence spectroscopy and two-dimensional coherent spectroscopy, respectively. This is a key milestone towards developing guidelines for populating large ensembles of exciton-polaritons, as required for polariton-based technologies. The work presented in this thesis moves us forward toward practical applications of room-temperature exciton-polaritons.
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2024-07-27
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Dissertation