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Nature Chemistry 6, 492–497 (2014); published online 4 May 2014; corrected after print 21 May 2014.10.1038/nchem.1945 In the version of this Article originally published, the author name Moungi G. Bawendi was missing the middle initial. This has now been corrected in the online versions of the Article.

We demonstrate a high-sensitivity ultrafast emission spectrometer based on the optical Kerr effect that time resolves emission simultaneously in the ultraviolet and visible ranges. We show that using benzene as the Kerr medium leads to the optimal balance between time-resolution and sensitivity of the optical shutter with low losses due to ultraviolet absorption. Using this medium together with high contrast broadband polarizers and charge-coupled device detection, we achieve efficient detection of emission transients (bandwidth >1.5 eV) in a time bin of ∼500 fs. To highlight the distinctive insights that can be gained by resolving complex subpicosecond dynamics in a single experiment, we present UV-visible transient emission spectra of technologically relevant wide bandgap zinc oxide. With an enhanced broadband detection, subpicosecond effects such as thermalization, bandgap renormalization, and carrier trapping can be easily assessed, with ramifications for optoelectronics and energy-related technologies.

As wide bandgap materials are nanostructured for optoelectronics and energy technologies, understanding how size and defects modify the carrier dynamics becomes critical. Here, we examine broadband ultraviolet-visible subpicosecond emission dynamics of prototypical ZnO in bulk, nanowire and nanosphere geometries. Using a high-sensitivity transient emission Kerr-based spectrometer, we probe exciton dynamics in the low fluence regime to determine how defects states impact thermalization and recombination rates. In contrast to steady-state measurements, we transiently identify low-energy emission features that originate from localized excitonic states rather than mid-gap states, characterized by distinct recombination kinetics, and correlate to longer thermalization times. These states are critical for understanding the overall excited state lifetime of materials in this size regime, where crystallinity rather than dimensionality plays a primary role in dictating recombination dynamics.

We report a chemical method by which graphitic carbon is prepared at reaction temperatures as low as 110 degrees C from readily available molecular reagents. This process requires no forcing conditions such as high pressures, intense light, or electrical discharge but is a simple, catalytic organometallic reaction. The carbon forms in a variety of morphologies including graphene sheets and nanotubes. The mild reaction conditions are similar to those routinely employed in homogeneous catalysis; therefore, they will allow the subtle manipulation of reaction variables to give desired morphologies selectively.

We report a tunable library of N,N,N′-trisubstituted selenourea precursors and their reaction with lead oleate at 60–150 °C to form carboxylate-terminated PbSe nanocrystals in quantitative yields. Single exponential conversion kinetics can be tailored over 4 orders of magnitude by adjusting the selenourea structure. The wide range of conversion reactivity allows the extent of nucleation ([nanocrystal] = 4.6–56.7 μM) and the size following complete precursor conversion (d = 1.7–6.6 nm) to be controlled. Narrow size distributions (σ = 0.5–2%) are obtained whose spectral line widths are dominated (73–83%) by the intrinsic single particle spectral broadening, as observed using spectral hole burning measurements. The intrinsic broadening decreases with increasing size (fwhm = 320–65 meV, d = 1.6–4.4 nm) that derives from exciton fine structure and exciton–phonon coupling rather than broadening caused by the size distribution.

Rayleigh scattering using high-brightness sources provides a sensitive and general tool to probe the electronic properties of nano-sized structures. This capability is demonstrated by recording the electronic transitions of individual single-wall carbon nanotubes.

We have obtained Raman spectra of the high-energy (G) modes from individual metallic carbon nanotubes. The Raman lines are broadened to widths up to 100 cm?1, indicating strong phonon damping by electron-hole pairs.

We demonstrate stimulated polariton emission at room temperature in a dielectric microcavity embedded with ZnO nanoparticles. The polariton lifetime is also shown to decrease drastically above the stimulated emission threshold.