Directional growth of ultralong nanowires (NWs) is significant for practical application of large-scale optoelectronic integration. Here, we demonstrate the controlled growth of in-plane directional perovskite CsPbBr NWs, induced by graphoepitaxial effect on annealed M-plane sapphire substrates. The wires have a diameter of several hundred nanometers, with lengths up to several millimeters. Microstructure characterization shows that CsPbBr NWs are high-quality single crystals, with smooth surfaces and well-defined cross section. The NWs have very strong band-edge photoluminescence (PL) with a long PL lifetime of ∼25 ns and can realize high-quality optical waveguides. Photodetectors constructed on these individual NWs exhibit excellent photoresponse with an ultrahigh responsivity of 4400 A/W and a very fast response speed of 252 μs. This work presents an important step toward scalable growth of high-quality perovskite NWs, which will provide promising opportunities in constructing integrated nanophotonic and optoelectronic systems.

Cesium lead halide perovskite nanowires have emerged as promising low-dimensional semiconductor structures for integrated photonic applications. Understanding light-matter interactions in a nanowire cavity is of both fundamental and practical interest in designing low-power-consumption nanoscale light sources. In this work, high-quality in-plane aligned halide perovskite CsPbX (X = Cl, Br, I) nanowires are synthesized by a vapor growth method on an annealed M-plane sapphire substrate. Large-area nanowire laser arrays have been achieved based on the as-grown aligned CsPbX nanowires at room temperature with quite low pumping thresholds, very high quality factors, and a high degree of linear polarization. More importantly, it is found that exciton-polaritons are formed in the nanowires under the excitation of a pulsed laser, indicating a strong exciton-photon coupling in the optical microcavities made of cesium lead halide perovskites. The coupling strength in these CsPbX nanowires is dependent on the atomic composition, where the obtained room-temperature Rabi splitting energy is ∼210 ± 13, 146 ± 9, and 103 ± 5 meV for the CsPbCl, CsPbBr, and CsPbI nanowires, respectively. This work provides fundamental insights for the practical applications of all-inorganic perovskite CsPbX nanowires in designing light-emitting devices and integrated nanophotonic systems.

Potassium‐based dual‐ion batteries (KDIBs) have emerged as a new generation of rechargeable batteries, due to their high cell voltage, low cost, and the natural abundance of potassium resources. However, the low capacity and poor cycling stability largely hinder the further development of KDIBs. Herein, the fabrication of hierarchically porous N‐doped carbon fibers (HPNCFs) as a free‐standing anode for high‐performance KDIBs is reported. With a free‐standing hierarchical structure (micro/meso/macropores and nanochannels) and high‐content of nitrogen doping, the HPNCFs not only provide intrinsic electron pathways and efficient ion transport channels, but also afford sufficient free space to tolerate the volume change during cycling. Consequently, the KDIBs made from a graphite cathode and an optimized HPNCFs anode deliver a high reversible capacity of 197 mAh g−1 at a specific current of 50 mA g−1, and excellent cycling stability (65 mAh g−1 after 346 cycles at a specific current of 100 mA g−1, the capacity calculation of the KDIBs is based on the mass of the anode). These results indicate that the properly designed HPNCFs can effectively improve the capacity and cycling stability of the KDIBs, indicating a great potential for applications in the field of high‐performance energy‐storage devices.

Nanoscale laser sources with downscaled device footprint, high energy efficiency, and high operation speed are pivotal for a wide array of optoelectronic and nanophotonic applications ranging from on-chip interconnects, nanospectroscopy, and sensing to optical communication. The capability of on-demand lasing output with reversible and continuous wavelength tunability over a broad spectral range enables key functionalities in wavelength-division multiplexing and finely controlled light–matter interaction, which remains an important subject under intense research. In this study, we demonstrate an electrically controlled wavelength-tunable laser based on a CdS nanoribbon (NR) structure. Typical “S”-shaped characteristics of pump power dependence were observed for dominant lasing lines, with concomitant line width narrowing. By applying an increased bias voltage across the NR device, the lasing resonance exhibits a continuous tuning from 510 to 520 nm for a bias field in the range 0–15.4 kV/cm. Systematic bias-dependent absorption and time-resolved photoluminescence (PL) measurements were performed, revealing a red-shifted band edge of gain medium and prolonged PL lifetime with increased electric field over the device. Both current-induced thermal reduction of the band gap and the Franz–Keldysh effect were identified to account for the modification of the lasing profile, with the former factor playing the leading role. Furthermore, dynamical switching of NR lasing was successfully demonstrated, yielding a modulation ratio up to ∼21 dB. The electrically tuned wavelength-reversible CdS NR laser in this work, therefore, presents an important step toward color-selective coherent emitters for future chip-based nanophotonic and optoelectronic circuitry.

Germanium (Ge) has gained a great deal of attention as an anode material for sodium ion batteries (SIBs) and lithium ion batteries (LIBs) for its high theoretical capacity and ion diffusivity. Unfortunately, Ge particle pulverization triggered by huge volume expansion during the alloying and dealloying processes can cause rapid capacity fade. Herein we report a facile method for the preparation of ultrafine Ge nanoparticles embedded in hierarchical N-doped multichannel carbon fibers (denoted as Ge-NMCFs) by electrospinning. The hierarchical carbon matrix not only provides sufficient internal void space to accommodate the large volume expansion of Ge nanoparticles, but also provides numerous open channels for the easy access of electrolyte and Na/Li ions. As half-cell tests revealed, the composite provides discharge capacity of 303 mA h g −1 (1st cycle) and 160 mA h g −1 (700th cycle) for SIBs, 1146.7 mA h g −1 (1st cycle) and 600 mA h g −1 (500th cycle) for LIBs at a current density of 500 mA g −1 (all the presented capacity based on the total weight of Ge/C composites). Density functional theory calculation suggests that N-doped in carbon can enhance the Na/Li ion storage and improve the electrochemical performance. This demonstration is an important step towards the development of SIBs and LIBs with much higher specific energy capacity and longer cycle stability.