Matthew Joseph Crane

The robust upconversion of infrared light would bypass its low photon energy, enabling efficient utilization. Here we employ hot thermal carriers produced through excitation of localized surface plasmon resonances in semiconductor nanocrystals to efficiently upconvert infrared photons. Transient absorption spectroscopy shows hot electron transfer from plasmonic tin-doped indium oxide (ITO) nanocrystals to semiconductor thin films, overcoming a 1.1 eV barrier via infrared photoexcitation at 0.56 eV. The rate of hot electron transfer is consistent with kinetic and power dependencies for hot thermal carriers and well described by Marcus Theory. Analysis reveals that the low, tailorable carrier concentration in ITO compared to metals enables this upconversion process. This mechanism facilitates electronic upconversion throughout the infrared without constraints imposed by absorption cross sections, phonon energies, or energetic barriers.

The robust upconversion of infrared light would bypass its low photon energy, enabling efficient utilization. Here we employ hot thermal carriers produced through excitation of localized surface plasmon resonances in semiconductor nanocrystals to efficiently upconvert infrared photons. Transient absorption spectroscopy shows hot-electron transfer from plasmonic tin-doped indium oxide (ITO) nanocrystals to semiconductor thin films, overcoming a 1.1 eV barrier via infrared photoexcitation at 0.52 eV. The rate of hot-electron transfer is consistent with kinetic and power dependencies for hot thermal carriers and well described by Marcus Theory. Analysis reveals the low, tailorable carrier concentration in ITO compared to metals enables this upconversion process. This mechanism facilitates upconversion throughout the infrared without constraints imposed by absorption cross sections, phonon energies, or energetic barriers.

Accurate single nanocrystal positioning tools are critical for emerging quantum and photonic technologies. Optical printing provides a platform to realize this positioning, but we need to understand the roles that solvent and surface functionalization play in controlling positional error, particularly for dielectric nanocrystals. Here, we characterize the impact of solvent and surface functionalization on nonresonant optical printing accuracy and efficacy, demonstrating accuracies of 50 nm. Changing solvent, nanocrystal concentration, and surface functionalization influences the number of attempts required to print nanocrystals, which we find is connected to positional error. Adding electrolytes to modify the interfacial DLVO potential reveals a unique regime where high irradiances minimize positional error while maximizing efficacy. Multiphysics simulations suggest that this regime results from photothermal effects and gradient forces. We validate these simulations by showing lower positional errors from substrates with higher absorption coefficients. These results will guide optical printing procedures for single nanocrystal positioning applications.

Harnessing hot carriers in plasmonic nanoparticles provides a promising paradigm for nonequilibrium photodetectors, photocatalysts, and photothermal technologies. Here, we show that the low carrier concentration in plasmonic Sn⁴⁺:In₂O₃ (ITO) nanocrystals enables efficient hot carrier generation and extraction via hot thermal carriers rather than athermal carriers. Using transient absorption spectroscopy, we measure hot carrier generation and transfer between ITO nanocrystals and Rhodamine B (RhB) adsorbates following infrared plasmonic excitation. Pump and fluence dependent experiments show that charge transfer arises from hot thermal carriers, which are efficiently generated due to ITO's low electron heat capacity and short electron-electron scattering time. Modeling the process with Marcus theory and a two-temperature model reveals that the hot thermal carrier transfer can exceed athermal carrier transfer at high rates of absorption. These data reveal clear guidelines to design plasmonic nanomaterials for hot thermal carrier generation and transfer.

Harnessing hot carriers in plasmonic nanoparticles provides a new paradigm for nonequilibrium photodetectors, photocatalysts, and photothermal technologies. Here, we show that the low carrier concentration in plasmonic Sn4+:In2O3 (ITO) nanocrystals enables a new platform for hot carrier generation and extraction via hot thermal carriers rather than hot athermal carriers. Using transient absorption spectroscopy, we measure hot carrier generation and transfer between ITO nanocrystals and Rhodamine B (RhB) adsorbates following infrared plasmonic excitation. Pump and fluence dependent experiments show that charge transfer arises from hot thermal carriers, which are efficiently generated due to ITO’s low electron heat capacity and electron-electron scattering time. Modelling the process with Marcus theory and a two temperature model reveals that the hot thermal carrier transfer can exceed hot athermal carrier transfer at rates of absorption. These data reveal clear guidelines for designing plasmonic nanomaterials for hot thermal carrier generation and transfer, paving the way for new hot carrier technologies.

The optical trapping of colloidal semiconductor nanomaterials would enable single-particle photophysics, sensing, and chemical measurements. Yet, the trapping of these materials has lagged behind other dielectric and metallic materials due to the prevalence of aqueous solvents in optical trapping experiments, which are not suitable for many semiconductors. Here, we trap particles in multiple solvents and study the impact of non-aqueous solvents on optical trapping dynamics. These experiments and calculations show that there exists an optimal refractive index of the media that maximizes trapping strength, and for semiconductor colloidal nanomaterials, a universal relationship to enhance trap strength. We also find that viscosity has no impact on the trap strength, and only changes the residence times of particles in unstable traps. These results provide an understanding of how solvent selection impacts trapping dynamics and general design rules for experiments in non-aqueous solvents, opening the door for improved sensing, chemistry, and photophysics studies using colloidal semiconductor nanomaterials.

The pressure-induced phase transformations of certain rare earth (RE) orthophosphates have attracted broad interest from geoscience to structural ceramics. Studying these transformations has required in situ Raman spectroscopy or synchrotron X-ray diffraction (XRD), each of which suffers from poor signal or limited accessibility, respectively. This study exploits the photoluminescence (PL) of Tb3+ ions and the unique sensitivity of PL to the local bonding environment to interrogate the symmetry-reducing xenotime-monazite phase transformation of TbPO4. At pressures consistent with the XRD-based phase transformation onset pressure of 8.7(6) GPa, PL spectra show new peaks emerging as well as trend changes in the centroids and intensity ratios of certain PL bands. Furthermore, PL spectra of recovered samples show transformation is irreversible. Hysteresis in certain PL band intensity ratios also reveals the stress history in TbPO4. This in situ PL approach can be applied to probe pressure-induced transformations and crystal field distortions in other RE-based oxide compounds.