Professor Robert Taylor

Abstract:

Conventional machine vision systems based on RGB cameras struggle to distinguish materials that appear visually identical, such as plastics of the same color and shape. To address this limitation, we present a spectrometer-free time-division multiplexed (TDM) near-infrared (NIR) time-of-flight (ToF) vision system that enables simultaneous acquisition of spectral and geometric information using dual-detector architecture composed of an avalanche photodiode (APD) for multispectral reflectance detection and a single-photon avalanche diode (SPAD) for ToF ranging. By extending TDM to multispectral NIR imaging, the proposed system temporally separates nanosecond laser pulses at 980 nm, 1450 nm, and 1650 nm for material discrimination, while an additional 905 nm channel provides high-precision ToF depth mapping. This architecture eliminates bulky spectrometers and dispersive optics, minimizing optical loss while maintaining compactness and scalability. The system successfully recognizes 12 visually similar materials, including six white plastics, three green rubbers, and three silver metals, based on their unique NIR reflectance fingerprints encoded into false-color RGB images. A convolutional neural network (CNN) trained on these images achieves near-perfect classification accuracy. Furthermore, a dual-domain experiment with a mannequin and a human subject demonstrates simultaneous reconstruction of surface geometry and material differentiation under realistic conditions. This spectrometer-free multispectral ToF vision approach establishes a compact and efficient sensing platform for high-precision robotic perception, intelligent manufacturing, and physical artificial intelligence systems requiring both spectral and spatial awareness.

Abstract:

CsPbCl3 perovskite nanocrystals (NCs) are promising violet emitters owing to their narrow emission and high color purity, but their low defect tolerance demands careful passivation to achieve high photoluminescence quantum yield (PLQY), and typically only for fresh CsPbCl3 NCs. Here, we report a delayed dual‐passivation pathway in CsPbCl3 NCs induced by the halide‐rich molecular reagent phosphorus oxychloride (POCl3), which unexpectedly yields a strong time‐dependent PLQY enhancement instead of the rapid degradation usually observed. POCl3 gradually decomposes into P‐ and Cl‐containing species, enabling a controlled release of excess halides that autonomously passivates halide vacancies in a self‐regulated manner. This dynamic self‐healing process boosts the PLQY of colloidal CsPbCl3 NCs by over 40‐fold relative to pristine samples and sustains high violet emission efficiencies for more than 2 months of storage under ambient conditions. Spectroscopic measurements and calculations indicate that both liberated Cl− and in situ—formed phosphonic species passivate halide vacancies and Pb2+ dangling bonds, suppressing mid‐gap defect states. The resulting self‐passivated NCs deliver a luminance of 409 cd m−2, the highest reported for CsPbCl3‐based violet emitters. These results establish halide‐rich dual passivators such as POCl3 as powerful tools for long‐term defect control in chloride perovskite NCs and for robust, bright violet‐LEDs.

Abstract:

Lead-halide perovskite nanocrystals (NCs) have gained attention for optoelectronics, but careful selection of the antisolvent used for purification is essential to achieve high monodispersity and yield while minimizing surface damage. Current understanding indicates that this requires lowering the relative polarity of the antisolvent, yet high-polarity antisolvents are widely used for purification, as we confirm through data mining. We show that polarity alone is insufficient for antisolvent selection by comparing ethyl acetate and acetonitrile for CsPbI3 NC purification. Despite its higher polarity, acetonitrile yields improved colloidal stability compared to ethyl acetate. Using 1H NMR, FTIR, and XPS measurements, alongside DFT calculations, we demonstrate that acetonitrile acts as a stronger Lewis base, binding to and passivating the NC surface. Coordination of acetonitrile to the perovskite NC surface enhances stability and improves their performance in light-emitting diodes. These findings establish a mechanistic framework for antisolvent selection to realize bright and stable halide perovskite NCs.

Abstract:

Graphene nanoribbons (GNRs) combine the remarkable optical and electronic properties of graphene with the presence of a tunable band gap, making them promising for optoelectronic applications. Here, we investigate the excitonic properties of individual cove-edge GNRs through microphotoluminescence (micro-PL) spectroscopy. We observe ultranarrow emission lines with full width at half-maximum as low as 24 μeV, demonstrating a reduction of inhomogeneous broadening by 3 orders of magnitude compared to GNR ensembles. Temperature-dependent PL reveals phonon-mediated broadening mechanisms, with electron–phonon coupling parameters in agreement with ensemble studies but with dramatically reduced line widths. Time-resolved PL suggests long-lived excitonic states, while spectral diffusion analysis demonstrates stable emission energies, highlighting the exceptional quality of these GNRs as single-photon emitters. The absence of intensity blinking and low Mandel parameters further support the robustness of the emission properties. Our findings establish cove-edge GNRs as promising candidates for quantum light sources and nanoscale optoelectronic applications.