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Despite broad applications in imaging, energy conversion, and telecommunications, few nanoscale moieties emit light efficiently in the shortwave infrared (SWIR, 1000–2000 nm or 1.24–0.62 eV). We report quantum-confined mercury chalcogenide (HgX, where X = Se or Te) nanoplatelets (NPLs) can be induced to emit bright (QY > 30%) and tunable (900–1500+ nm) infrared emission from attached quantum dot (QD) “defect” states. We demonstrate near unity energy transfer from NPL to these QDs, which completely quench NPL emission and emit with a high QY through the SWIR. This QD defect emission is kinetically tunable, enabling controlled midgap emission from NPLs. Spectrally resolved photoluminescence demonstrates energy-dependent lifetimes, with radiative rates 10–20 times faster than those of their PbX analogues in the same spectral window. Coupled with their high quantum yield, midgap emission HgX dots on HgX NPLs provide a potential platform for novel optoelectronics in the SWIR.

Rational design of bright near and shortwave infrared (NIR: 700–1000 SWIR: 1000–2000 nm) molecular and nanoscale emitters is a fundamental scientific question with applications ranging from deep tissue imaging to new photonic materials. However, all reported organic chromophores with energy gaps in the SWIR have very low quantum yields. Is this the result of a fundamental limit for the quantum yield of organic chromophores in the SWIR? Here we combine experiment and theory to derive an energy gap quantum yield master equation (EQME), which describes the fundamental limits in SWIR quantum yields for organic chromophores in terms of energy gap laws for radiative and nonradiative decay. We parametrize EQME using experimental data from time-correlated single photon counting in the SWIR acquired using superconducting nanowire single photon detectors operating beyond the bandgap of silicon. Evaluating the photophysics of 21 polymethine NIR/SWIR emissive chromophores, we explain the precipitous decline of past 900 nm as the result of decreased radiative rates and increased nonradiative deactivation via high frequency vibrations as a function of singlet energy gap. From EQME we can compare quantum yields among NIR/SWIR chromophores while accounting for changes in energy gaps. We find that electron donating character on polymethine heterocycles results in improvements of radiative parameters obscured by a simultaneous redshift. We correlate this improvement to changes in transition dipole moments across the chromenylium polymethine family. Finally, understanding energy gap laws reveals quantitative estimates of the effect of deuteration and molecular aggregation as strategies to increase in the SWIR. We experimentally demonstrate that partial deuteration of the chromophore Flav7 results in decreased nonradiative rates and concomitant increases in quantum yield. These insights will enable optimal chromophore designs for SWIR fluorescence.

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.

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