Transition metal oxides such as TiO2 and CeO2 are wide bandgap semiconductors with photocatalytic properties used to drive electrical currents and enhance electrochemical reactions. The utility of wide bandgap semiconductors can be extended from the UV and into the visible by embedding metal nanoparticles into the semiconductor. Excitation of localized surface plasmon resonances in the metal nanoparticle generates free electrons that can be injected into the semiconductor and extend the photoactivity range using lower energy photons. In this work, ultrafast transient absorption spectroscopy is used to investigate the hot electron injection from Cu nanoparticles photodeposited onto a CeO2 aerogel.
2D perovskites have broad technological appeal because of their tunable mechanical, optical, and electrical properties. For flexible optoelectronic applications, it is necessary to determine how mechanical stresses affect their optoelectronic properties. We compare the impact of strain on the photoluminescence (PL) spectra and charge carrier recombination rates of two different 2D perovskite materials, synthesized using either phenethylammonium or butylammonium cations. Both perovskite materials exhibit strong PL enhancement, redshifts of the PL emission wavelength, and longer recombination lifetimes for compressive strains of ≲1%. These results are discussed in relation to the materials’ band structures and trap states.
2D perovskites, consisting of alternating layers of metal halide sheets and cations, tend to be more environmentally robust compared to their bulk 3D counterpart and have broad technological appeal because of their tunable mechanical, optical, and electrical properties. While these materials have promise for flexible optoelectronic applications, it is necessary to determine the impact of strain on the perovskite optical and electronic properties. Here, we discuss our work in understanding how strain modifies the carrier dynamics of 2D perovskites using time resolved spectroscopy. We compare the photoluminescence lifetime of two different 2D perovskite materials, synthesized using either phenethylammonium or butylammonium cations. Both perovskite materials exhibit about a 50% decrease in the lifetime for tensile strains <1%. The decrease in the photoluminescence lifetime, indicating a decrease in the charge carrier lifetime, is discussed in relation the materials defect states and bands
The mid-infrared spectra of many polar materials are dominated by highly reflective reststrahlen bands that occur between the transverse and longitudinal optical phonons. Within the reststrahlen bands, light can couple with optical phonons to support phonon-polariton modes. These modes enhance light-matter interactions through the concentration of light to nanoscale dimensions, and therefore, are particularly promising for mid-infrared nanophotonic applications. Here, we discuss our work on expanding the spectral range over which phonon-polaritons are supported by using new material systems, as well as active tuning of the modes via carrier photoinjection. In particular, we report on the confinement of hyperbolic phonon-polaritons in calcite, a ubiquitous polar material. We also report the use of the LO-phonon-plasmon-coupling (LOPC) effect to actively tune the Berreman mode of a GaN thin film.
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