We describe and implement an interferometric approach to decay-associated photoluminescence spectroscopy, which we term decay-associated Fourier spectroscopy (DAFS). In DAFS, the emitted photon stream from a substrate passes through a variable path length Mach− Zehnder interferometer prior to detection and timing. The interferometer encodes spectral information in the intensity measured at each detector enabling simultaneous spectral and temporal resolution. We detail several advantages of DAFS, including wavelength-range insensitivity, drift-noise cancellation, and optical mode retention. DAFS allows us to direct the photon stream into an optical fiber, enabling the implementation of superconducting nanowire single photon detectors for energy-resolved spectroscopy in the shortwave infrared spectral window (λ = 1−2 μm). We demonstrate the broad applicability of DAFS, in both the visible and shortwave infrared, using two Forster resonance energy transfer pairs: a pair operating with conventional visible wavelengths and a pair showing concurrent acquisition in the visible and the shortwave infrared regime.
We demonstrate the preparation of mesoscale semiconductor (II–VI) nanoplatelets (NPLs) for the first time using colloidal seeded growth. These nanoplatelets are quantum-confined and atomically precise but grown to a length scale compatible with conventional optical imaging and microscopic manipulation (even reaching >1 μm2) offering an opportunity to bridge the application space between nanocrystals and two-dimensional (2D) materials. Using CdTe as a model system, we develop a seeded growth procedure, show the parameters that control extension, and apply them to a variety of thicknesses and compositions. In situ spectroscopy demonstrates that addition onto the nanoplatelet seeds is not continuous and likely occurs through ripening. Finally, we use correlative optical and electron microscopy to demonstrate that at large sizes, photoluminescence (PL) mapping of the entire structure can be resolved including spatial inhomogeneities. Overall, these results show that nanoplatelets can be compared to 2D semiconductors while maintaining the advantages of scalable colloidal synthesis, thickness tunability, and solution processability.
We demonstrate a method for separating and resolving the dynamics of multiple emitters without the use of conventional filters. By directing the photon emission through a fixed path-length imbalanced Mach−Zehnder interferometer, we interferometrically cancel (or enhance) certain spectral signatures corresponding to one emissive species. Our approach, Spectrally selective Time-resolved Emission through Fourier-filtering (STEF), leverages the detection and subtraction of both outputs of a tuned Mach−Zehnder interferometer, which can be combined with time-correlated single photon counting (TCSPC) or confocal imaging to demix multiple emitter signatures. We develop a procedure to calibrate out imperfections in Mach−Zehnder interferometry schemes. Additionally, we demonstrate the range and utility of STEF by performing the following procedures with one measurement: (1) filtering out laser scatter from a sample, (2) separating and measuring a fluorescence lifetime from a binary chromophore mixture with overlapped emission spectra, (3) confocally imaging and separately resolving the standard fluorescent stains in bovine pulmonary endothelial cells and nearly overlapping fluorescent stains on RAW 264.7 cells. This form of spectral balancing can allow for robust and tunable signal sorting.
Natural photosystems couple light harvesting to charge separation using a “special pair” of chlorophyll molecules that accepts excitation energy from the antenna and initiates an electron-transfer cascade. To investigate the photophysics of special pairs independent of complexities of native photosynthetic proteins, and as a first step towards synthetic photosystems for new energy conversion technologies, we designed C2-symmetric proteins that precisely position chlorophyll dimers. X-ray crystallography shows that one designed protein binds two chlorophylls in a binding orientation matching native special pairs, while a second positions them in a previously unseen geometry. Spectroscopy reveals excitonic coupling, and fluorescence lifetime imaging demonstrates energy transfer. We designed special pair proteins to assemble into 24-chlorophyll octahedral nanocages; the design model and cryo-EM structure are nearly identical. The design accuracy and energy transfer function of these special pair proteins suggest that de novo design of artificial photosynthetic systems is within reach of current computational methods.
Colloidally grown (II-VI) semiconductor nanoplatelets display significantly smaller lateral dimensions than their mechanically exfoliated 2D van der Waal (vdW) semiconductor counterparts. Here, we show that a seeded growth procedure allows us to significantly extend the lateral area of atomically precise nanoplatelets to the mesoscale (>1 μm^2). Using CdTe nanoplatelets as a model system, we optimize reaction parameters to expand a variety of nanoplatelets with different thickness and compositions. In situ spectroscopy results demonstrate that large NPLs grow through a mechanism of lateral ripening of seeds. Correlative optical spectroscopy and electron microscopy measurements show that the photoluminescence displays resolvable spatial inhomogeneities, similar to 2D semiconductors. Overall, these mesoscale nanoplatelets can be analogized to vdW semiconductors, with the added advantages of scalable colloidal synthesis, thickness tunability and solution processability.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.