The magnetic plasmons of three-dimensional nanostructures have unique optical responses and special significance for optical nanoresonators and nanoantennas. In this study, we have successfully synthesized colloidal Au and AuAg nanocups with a well-controlled asymmetric geometry, tunable opening sizes, and normalized depths (h/ b, where h is depth and b is the height of the templating PbS nanooctahedrons), variable magnetic plasmon resonance, and largely enhanced second-harmonic generation (SHG). The most-efficient SHG of the bare Au nanocups is experimentally observed when the normalized depth h/b is adjusted to ∼0.78−0.79. We find that the average magnetic field enhancement is maximized at h/b = ∼0.65 and reveal that the maximal SHG can be attributed to the joint action of the optimized magnetic plasmon resonance and the "lightning-rod effect" of the Au nanocups. Furthermore, we demonstrate for the first time that the AuAg heteronanocups prepared by overgrowth of Ag on the Au nanocups can synergize the magnetic and electric plasmon resonances for nonlinear enhancement. By the tailoring of the dual resonances at the fundamental excitation and second-harmonic wavelengths, the far-field SHG intensity of the AuAg nanocups is enhanced 21.8fold compared to that of the bare Au nanocups. These findings provide a strategy for the design of nonlinear optical nanoantennas based on magnetic plasmon resonances and can lead to diverse applications ranging from nanophotonics to biological spectroscopy.

We report the preparation of monolayer (n = 1), few-layer (n = 2–5) and 3D (n = ∞) organic lead bromide perovskite nanoplatelets (NPLs) by tuning the molar ratio of methylammonium bromide (MABr) and hexadecammonium bromide (HABr). The absorption spectrum of the monolayer (HA)2PbBr4 perovskite NPLs shows about 138 nm blue shift from that of 3D MAPbBr3 perovskites, which is attributed to strong quantum confinement effect. We further investigate the two-photon photoluminescence (PL) of the NPLs and measure the exciton binding energy of monolayer perovskite NPLs using linear absorption and two-photon PL excitation spectroscopy. The exciton binding energy of monolayer perovskite NPLs is about 218 meV, which is far larger than tens of meV in 3D lead halide perovskites.

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Pure BiFeO3, Bi2Fe4O9, and BiFeO3/Bi2Fe4O9 heterostructure nanofibers were successfully synthesized by a facile wet chemical process followed by an electrospinning technique. Compared with the pure BiFeO3 and Bi2Fe4O9 nanofibers, the introduction of Bi2Fe4O9 in the BiFeO3 makes its absorption edge red shift to absorb much more visible light, and improves its separation efficiency of photogenerated carrier. Besides, the as-obtained BiFeO3/Bi2Fe4O9 nanofibers exhibit higher photocatalytic activity in both the degradation of Rhodamine B and H2 evolution from water under visible-light irradiation. The BiFeO3/Bi2Fe4O9 nanofibers exhibited about 2.7 times and 2.0 times higher H2 evolution than that of pure BiFeO3 and pure Bi2Fe4O9 samples, respectively. The possible photoreactive mechanism of the BiFeO3/Bi2Fe4O9 nanofibers was carefully investigated according to the results of photocatalytic and photoelectric performance, and a Z-scheme mechanism was proposed. Such BiFeO3/Bi2Fe4O9 heterostructure and its composing strategy may bring new insight into the designing of highly efficient visible-light-responsible photocatalysts.

Plasmon-mediated energy transfer is highly desirable in photo-electronic nanodevices, but the direct injection efficiency of "hot electrons" in plasmonic photo-detectors and plasmon-sensitized solar cells (plasmon-SSCs) is poor. On another front, Fano resonance induced by strong plasmon-exciton coupling provides an efficient channel of coherent energy transfer from metallic plasmons to molecular excitons, and organic dye molecules have a much better injection efficiency in exciton-SSCs than "hot electrons". Here, we investigate enhanced light-harvesting of chlorophyll-a molecules strongly coupled to Au nanostructured films via Fano resonance. The enhanced local field and plasmon resonance energy transfer are experimentally revealed by monitoring the ultrafast dynamical processes of the plexcitons and the photocurrent flows of the assembled plexciton-SSCs. By tuning the Fano factor and anti-resonance wavelengths, we find that the local field is largely enhanced and the efficiency of plexciton-SSCs consisting of ultrathin TiO2 films is significantly improved. Most strikingly, the output power of the plexciton-SSCs is much larger than the sum of those of the individual plasmon- and exciton-SSCs. Our observations provide a practical approach to monitor energy and electron transfer in plasmon-exciton hybrids at a strong coupling regime and also offer a new strategy to design photovoltaic nanodevices.