We demonstrate, experimentally and theoretically, that the photon emission from gold nanorods can be viewed as a Purcell effect enhanced radiative recombination of hot carriers. By correlating the single-particle photoluminescence spectra and quantum yields of gold nanorods measured for five different excitation wavelengths and varied excitation powers, we illustrate the effects of hot carrier distributions evolving through interband and intraband transitions and the photonic density of states on the nanorod photoluminescence. Our model, using only one fixed input parameter, describes quantitatively both emission from interband recombination and the main photoluminescence peak coinciding with the longitudinal surface plasmon resonance.

The origin of light emission from plasmonic nanoparticles has been strongly debated lately. It is present as the background of surface-enhanced Raman scattering and, despite the low yield, has been used for novel sensing and imaging applications because of its photostability. Although the role of surface plasmons as an enhancing antenna is widely accepted, the main controversy regarding the mechanism of the emission is its assignment to either radiative recombination of hot carriers (photoluminescence) or electronic Raman scattering (inelastic light scattering). We have previously interpreted the Stokes-shifted emission from gold nanorods as the Purcell effect enhanced radiative recombination of hot carriers. Here we specifically focused on the anti-Stokes emission from single gold nanorods of varying aspect ratios with excitation wavelengths below and above the interband transition threshold while still employing continuous wave lasers. Analysis of the intensity ratios between Stokes and anti-Stokes emission yields temperatures that can only be interpreted as originating from the excited electron distribution and not a thermally equilibrated phonon population despite not using pulsed laser excitation. Consistent with this result as well as previous emission studies using ultrafast lasers, the power-dependence of the upconverted emission is nonlinear and gives the average number of participating photons as a function of emission wavelength. Our findings thus show that hot carriers and photoluminescence play a major role in the upconverted emission.

Exploiting useful contacts: The exceptional catalytic performance of a photocatalyst composed of Pd nanoparticles and mesoporous carbon nitride for the dehydrogenation of formic acid in water at room temperature to produce H2 gas (see picture) is due to enhanced electron enrichment of the Pd nanoparticles through charge transfer at the interface of the Mott–Schottky contact.

Removing effects of sample heterogeneity through single-molecule and single-particle techniques has advanced many fields. While background free luminescence and scattering spectroscopy is widely used, recording the absorption spectrum only is rather difficult. Here we present an approach capable of recording pure absorption spectra of individual nanostructures. We demonstrate the implementation of single-particle absorption spectroscopy on strongly scattering plasmonic nanoparticles by combining photothermal microscopy with a supercontinuum laser and an innovative calibration procedure that accounts for chromatic aberrations and wavelength-dependent excitation powers. Comparison of the absorption spectra to the scattering spectra of the same individual gold nanoparticles reveals the blueshift of the absorption spectra, as predicted by Mie theory but previously not detectable in extinction measurements that measure the sum of absorption and scattering. By covering a wavelength range of 300 nm, we are furthermore able to record absorption spectra of single gold nanorods with different aspect ratios. We find that the spectral shift between absorption and scattering for the longitudinal plasmon resonance decreases as a function of nanorod aspect ratio, which is in agreement with simulations.

The study of acoustic vibrations in nanoparticles provides unique and unparalleled insight into their mechanical properties. Electron-beam lithography of nanostructures allows precise manipulation of their acoustic vibration frequencies through control of nanoscale morphology. However, the dissipation of acoustic vibrations in this important class of nanostructures has not yet been examined. Here we report, using single-particle ultrafast transient extinction spectroscopy, the intrinsic damping dynamics in lithographically fabricated plasmonic nanostructures. We find that in stark contrast to chemically synthesized, monocrystalline nanoparticles, acoustic energy dissipation in lithographically fabricated nanostructures is solely dominated by intrinsic damping. A quality factor of Q = 11.3 ± 2.5 is observed for all 147 nanostructures, regardless of size, geometry, frequency, surface adhesion, and mode. This result indicates that the complex Young's modulus of this material is independent of frequency with its imaginary component being approximately 11 times smaller than its real part. Substrate-mediated acoustic vibration damping is strongly suppressed, despite strong binding between the glass substrate and Au nanostructures. We anticipate that these results, characterizing the optomechanical properties of lithographically fabricated metal nanostructures, will help inform their design for applications such as photoacoustic imaging agents, high-frequency resonators, and ultrafast optical switches.

We report a study of the shape-dependent spectral response of the gold nanoparticle surface plasmon resonance at various electron densities to provide mechanistic insight into the role of capacitive charging, a topic of some debate. We demonstrate a morphology-dependent spectral response for gold nanoparticles due to capacitive charging using single-particle spectroscopy in an inert electrochemical environment. A decrease in plasmon energy and increase in spectral width for gold nanospheres and nanorods was observed as the electron density was tuned through a potential window of -0.3 to 0.1 V. The combined observations could not be explained by existing theories. A new quantum theory for charging based on the random phase approximation was developed. Additionally, the redox reaction of gold oxide formation was probed using single-particle plasmon voltammetry to reproduce the reduction peak from the bulk cyclic voltammetry. These results deepen our understanding of the relationship between optical and electronic properties in plasmonic nanoparticles and provide insight toward their potential applications in directed electrocatalysis.

A magnetically recyclable carbon nitride supported Au−Co nanoparticles (Au−Co@CN) displayed exceedingly high photocatalytic activity for hydrolysis of aqueous ammonia borane (NH 3 BH 3 , AB) solution. Combined with a synergetic effect between Au and Co nanoparticles, the Motty−Schottky effect at the metal−semiconductor interface remarkably facilitated the catalytic performance of the Au−Co@CN catalyst on the hydrolysis of AB. The TOF value of Au−Co@CN catalyst is 2897 mol H 2 mol −1 metal h −1 at 298 K under visible light irradiation, which is more than 3 times higher than that of the benchmarked catalyst, PVP-stabilized Au@Co nanoparticles.

During the past decades, many efforts have been devoted to activation of the strong C À H bond in methane under mild conditions [1][2][3][4] because through suitable conversion methane may be used to substitute for the dwindling petroleum resources as a chemical feedstock. Among the various strategies is a compelling approach that uses photoenergy to drive the conversion of methane to more valuable molecules through dehydrogenation at room temperature. Yoshida et al. developed several effective photocatalysts, such as the ternary oxide SiO 2 -Al 2 O 3 -TiO 2 , [5] for methane conversion. Recently, we used zinc to modify the medium-pore ZSM-5 zeolite and found that the resulting material exhibits substantial photocatalytic activity for the selective conversion of methane to ethane and hydrogen under ultraviolet (UV) irradiation. [6] However, there are still huge challenges in finding more powerful systems to achieve a practical product yield and to exploit solar energy more effectively for the photodriven conversion of methane. It is now a consensus that the H 3 CÀH bond cleavage process is a key step in the dehydrogenation and dimerization of methane. [7,8] Investigations into this process provide insights into the essence of methane conversion at a molecular level, and thus enable us to design better performing systems. Nevertheless, only limited information about the mechanism for the photoinduced cleavage of the H 3 C À H bond occurring on substrate surfaces has been revealed so far, [9] and the nature of the photoactive species responsible for the methane C À H activation has yet to be elucidated in more detail. Previously, two models for the photoactivation of the methane CÀH bond were proposed. One considers that the presence of oxygen-centered radicals brings about homolytic CÀH bond cleavage, [10] whereas in the other highly dispersed metal species are believed to be the active sites of methane dehydrogenation. [6,11] Herein, we describe a Ga 3+ -modified ETS-10 zeolite material (ETS-10 = titanosilicate) in which the photogenerated hydroxyl radical and the extraframework metal ion interact with the methane molecule to split the H 3 CÀH bond in a synergistic way under UV irradiation (l < 350 nm). It is demonstrated that the combination of both oxygen-centered and metal-centered active sites in the material significantly enhances its photoactivity for methane CÀH bond activation, leading to efficient non-oxidative coupling of methane at room temperature. An average methane conversion rate of around 29.8 mmol h À1 g À1 was achieved after UV irradiation for 5 h, which is 3 and 20 times faster than those of Zn +modified ZSM-5 zeolite and SiO 2 -Al 2 O 3 -TiO 2 material (the two best photocatalysts for methane conversion developed so far), respectively.ETS-10 is a microporous titanosilicate with a framework containing one-dimensional O-Ti-O-Ti-O semiconducting nanowires (diameter of 0.67 nm) insulated from one another by the surrounding SiO 2 matrix ( Figure 1). [12] The combination of quantum-confined titanate...