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Layered transition metal dichalcogenides (TMDs) are a promising platform for new photonic and optoelectronic devices. Exciton‐phonon interaction is critical in determining their characteristics such as the exciton coherence lifetime and linewidth. However, the exciton linewidth obtained by conventional reflection spectrum is greatly affected by the background signals, and the research into exciton‐phonon coupling difference induced by stacking‐order in multi‐layer structures is still lacking. In this work, the temperature‐dependent exciton linewidths of CVD‐grown large‐area monolayer, 2H and 3R‐stacking bilayer WS2 based on a self‐designed reflective magnetic circular dichroism (MCD) spectrum are systematically investigated. It is found that 2H‐bilayer WS2 exhibits significantly larger exciton linewidth compared with monolayer and 3R bilayer, which can be attributed to the appearance of new phonon‐assisted relaxation channels caused by interlayer coupling. Meanwhile, 3R bilayer with a redshifted exciton peak has a narrower linewidth than 2H phase because the interlayer hopping is suppressed, resulting in the absence of interlayer scattering channel. These results provide intuitive evidence for the exciton linewidth‐broadening and exciton‐phonon coupling in different stacked layers and open up new vistas for the development of TMD‐based narrow‐linewidth nano‐sensors devices. [ABSTRACT FROM AUTHOR]

Heterostructured transition metal dichalcogenides (TMDs) have received much attention due to their tunable optical and electronic properties. Here, a strategy for facile fabrication of porous anodic alumina (PAA) membrane‐supported monolayer molybdenum disulfide (MoS2) is described. PAA is either empty or filled with gold nanoparticles (AuNPs). Such nanopore/nanosphere‐supported MoS2 (i.e., PAA‐MoS2 and PAA‐Au‐MoS2) exhibits greatly enhanced optical performances compared with those of silicon wafer‐supported MoS2 (i.e., Si/SiO2‐MoS2). Notably, 11‐fold Raman enhancement, 13‐fold photoluminescence enhancement, and 419‐fold second‐harmonic generation enhancement are achieved in PAA‐Au‐MoS2. Moreover, the optical enhancement mechanism of this unique structure is proposed. This work provides a platform for the construction of curved/heterostructured TMDs and exploration of their strong light‐matter interactions. [ABSTRACT FROM AUTHOR]

Herein, the piezoelectric effect of CsPbBr3 perovskite is utilized for the first time to enhance the nanolasers performance based on the flexible poly(ethylenenaphthalate) PEN/single‐crystal‐Au/MgF2/CsPbBr3 (ScAu/M/CPB) structure. The dynamic‐modulated plasmonic lasing mode blueshift is achieved by the piezoelectric polarization effect (PPE)‐induced effective refractive index (neff) change by varying the applied strain (ε). In particular, taking advantage of the increased cavity mode frequency, the lasing threshold (Pth) reduces from 4.5 µJ cm−2 (ε = 0) to 1.5 µJ cm−2 (ε = −1.02%). The ε‐dependent carrier dynamics results reveal the nature of ultralow Pth being PPE‐induced spontaneous emission (SE) decay rate enhancement, leading to the reduction in radiation loss of the plasmonic cavity. The corresponding enhancement mechanism is put forward to elucidate the principle of piezoelectric‐induced dynamic modulation nanolasers characteristic. This work demonstrates that coupling of piezoelectric effect and plasmonics is an effective route to enhance the performance of plasmonic nanolasers. [ABSTRACT FROM AUTHOR]

Manganese dioxide (MnO2) is considered to be one of the nanomaterials with enormous value in research and application because of its high theoretical specific capacitance, large specific surface area and porosity, excellent electron transfer ability, and excellent light absorption ability. However, exploring superior nonlinear absorption of MnO2 in the broadband spectrum is still the key challenge to harvesting their greatest potential. In this paper, the optical modulator based on MnO2 is fabricated, and its nonlinear optical performance is measured. The results indicate that the modulation depth is 4.4% and the saturable intensity is 32.8 MW cm−2 at 1.5 µm region. What's more fascinating is that the modulator based on MnO2 is integrated into Er‐doped and Tm‐doped fiber resonators to successfully demonstrate its broadband mode‐locking operations. The coexistence of harmonic bound state pulse and conventional soliton pulse, as well as dual‐wavelength solitons, have been obtained in a communication window and conventional soliton in a 2 µm‐band can be also achieved. This demonstrates that MnO2 serves as a broadband optical modulator, which makes MnO2 more competitive in the future ultrafast photonics and helps to expand the frontier of photonic technology. [ABSTRACT FROM AUTHOR]

Cadmium‐based nanoplatelets as optical display and lasing materials are widely explored and exhibit great advantages, owing to their narrow emission linewidths, anisotropic transition‐dipole distributions, and low lasing thresholds. However, in the green range, the photoluminescence quantum yield (PLQY) and emission tunability of nanoplatelets are still inferior to that of quantum dots. In this work, a new synthesis protocol is developed, enabling core/crown nanoplatelets to grow continuously from elementary precursors to their final form. A new heterostructure of CdSe/CdSeS core/alloyed‐crown nanoplatelets is produced that realizes 100% PLQY, the continuous tunability of emission peaks in between 502 and 550 nm, and low full‐width‐at‐half‐maximum (FWHM) of less than 15 nm. Achieving these excellent properties in all three aspects at the same time is unprecedented. In addition, the time‐resolved photoluminescence (TRPL) spectra of these nanoplatelets show a mono‐exponential decay characteristic, and the nanoplatelet film can also show 100% PLQY and a mono‐exponential decay characteristic, indicating the suppression of trap states. The high‐quality nanoplatelets achieved in this work provide a solid foundation for developing nanoplatelet‐based light sources, like light‐emitting diodes and lasers, with much higher efficiency, color purity, and lower working thresholds. [ABSTRACT FROM AUTHOR]

In 2D transition metal dichalcogenides (TMDs), trions have important applications in fundamental studies of multibody phenomena, novel optoelectronic devices, and valleytronic devices. However, the enhancement of trion emission, and in particular how the carrier dynamics is influenced when coupled with plasmonic cavity, is important for a deep understanding of trions and their further utilization. In this study, strong trion emission is achieved by coupling monolayer WS2 with a plasmonic nanocavity. Temperature‐dependent photoluminescence, dark‐field scattering measurement, and transient absorption spectroscopy are employed to investigate the trion and exciton behaviors in the hybrid structure. In plasmonic nanocavity, trion emission is enhanced by an order of magnitude, which is attributed to the conversion of excitons to trions via capturing photoionized carriers facilitated by Fano resonance. Further, the ultrafast dynamics of trions and excitons suggest that the plasmonic nanocavity enhances the hole cooling process and radiative recombination of excitons, as well as the formation and recovery process of trions. The results not only explain the enhancement of trion emission and carrier dynamics in the hybrid system but also provide one feasible method to obtain strong trion emission in TMDs, which makes the hybrid system a promising candidate for optoelectronic and valleytronic applications. [ABSTRACT FROM AUTHOR]

Muscovite mica is a widely used van der Waals epitaxial substrate for growing high‐quality low‐dimensional crystals owing to its nondangling surface. However, there is a recent debate on the surface atomic arrangement, especially the lattice symmetry, of the cleaved muscovite (001), which is not only crucial for the crystal heteroepitaxy dynamics on the substrate, but also fundamental to optoelectronic devices based on few‐layered muscovite. Herein, the surface reconstruction of the cleaved muscovite (001) is investigated by using high‐resolution atomic force microscopy, which reveals that the removal of interlayer potassium induces a distortion to aluminosilicate tetrahedra by depressing the connecting oxygen, breaking the intrinsic quasi‐hexagonal symmetry and resulting in bunched grooves along the [100] direction. These grooves enable vapor‐phase graphoepitaxy of millimeter‐scale, unidirectional single‐crystalline CsPbBr3 nanowire arrays without inducing unfavorable structural defects. Optical spectroscopy studies demonstrate their high optical quality and potential for anisotropic optoelectronic applications. These results further the understanding of epitaxial dynamics of muscovite (001), promote muscovite a powerful graphoepitaxy platform for anisotropic nanostructures, and provide insights into the development of few‐layered muscovite optoelectronic/proton devices. [ABSTRACT FROM AUTHOR]

Abstract: The recent emergence of metal‐halide perovskites as light absorbers in solar cells has attracted lots of attention on their synthesis and properties. In particular, low‐dimensional metal‐halide perovskites like platelets and wires are expected to regulate their optical and electrical properties in reference to bulk counterparts as a result of quantum confinement and anisotropy. In this review, first, the recent solution‐ and vapor‐based approaches on synthesizing metal‐halide perovskite platelets and wires are highlighted. Then, their optical and electrical properties along with application in photonics and optoelectronics such as lasers, light emitting diodes, photodetectors, and phototransistors are discussed. At last, the importance of such perovskite platelets and wires on improving material stability and transport properties is emphasized, and potential integration of perovskites with other low‐dimensional materials in multifunctional systems is proposed. [ABSTRACT FROM AUTHOR]

The carrier recombination dynamics in ZnSe nanowires (NWs) remain poorly understood despite more than a decade of research since their inception in 2001. Herein, through a comprehensive pump fluence‐ and temperature‐dependent two‐photon excitation (TPE) study, a clear picture of the carrier relaxation pathways, intrinsic lifetimes, exciton oscillator strengths, and exciton‐phonon interactions is presented for this NW system. Contrary to a common perception that the higher pump intensities needed to achieve two‐photon‐excited photoluminescence correspond to a higher exciton density threshold (nth) for two‐photon pumped lasing, it is found that a much lower nth is needed to achieve lasing with TPE compared to single‐photon excitation (SPE) of the same ZnSe NWs. This measurement is further supported by the greatly enhanced lasing action photostability characteristics of the ZnSe NWs under TPE. These findings have significant implications on the design and the tailoring of the optoelectronic properties of nanowire lasers. [ABSTRACT FROM AUTHOR]

Manipulating the bandgap structure and carrier distribution of multilayer transition metal dichalcogenides (TMDs) is crucial for improving their fluorescence efficiency and extending their optoelectronic applications. Herein, the evolution of the conduction band minimum of multilayer WSe2 as a function of the temperature and thickness is experimentally demonstrated and an ≈70‐fold fluorescence enhancement of the K–K direct emission is observed at 560 K in multilayer WSe2 flakes (≈170 nm) by heat engineering. This abnormal enhancement is attributed to thermally driven carrier redistribution achieved via intervalley transfer, which is confirmed by the theoretical calculations and temperature‐dependent time‐resolved photoluminescence. In addition, a threshold temperature of the intervalley transfer is proposed to describe the on‐state of the carrier redistribution model. The corresponding threshold temperature is determined to be ≈580 K, which is consistent with the temperature at which the maximum photoluminescence enhancement is observed. The study provides a useful strategy to optimize the optical and electric performances of multilayer WSe2 and other TMDs materials. [ABSTRACT FROM AUTHOR]

As an important 2D layered metal dichalcogenide, germanium diselenide (GeSe2) with a direct wide bandgap is attracting increasing attention for its potential applications in ultraviolet (UV) detection. However, only few‐layer GeSe2 has been reported to date. Here, a joint theoretical–experimental study on the optical and electronic properties of monolayer GeSe2 is presented, and monolayer GeSe2 is shown to have a direct wide bandgap of 2.96 eV. Consequently, monolayer GeSe2 does not respond to a major fraction of the visible spectrum. Notably, the photofield effect transistors based on the GeSe2 monolayer show p‐type behavior, high responsivity, superior detectivity, and a fast response time, competitive with state‐of‐the‐art UV detectors. In addition to the excellent photoresponse properties, 2D GeSe2 crystals also exhibit perpendicular optical reversal of the linear dichroism and polarized photodetection under wavelength modulation. Theoretical calculations of the band structure are used to shed light on these experimental results. The findings suggest that 2D GeSe2 is a promising candidate for highly selective polarization‐sensitive UV detection. [ABSTRACT FROM AUTHOR]

Continuous‐wave (CW) operated lasers are regarded as a stepping stone to the development of electrically driven lasers and crucial for practical application in high‐density integrated optoelectronic devices. Recently, metallic halide perovskites are demonstrated as excellent gain materials for CW lasers owing to their large optical absorption coefficient, low defect density, long diffusion length, and suppressed Auger recombination rate. Here, the latest research advances on CW pumped perovskite lasers are reviewed. First, the recent research advances on CW lasing in perovskite thin film are highlighted. Then, CW lasing in CsPbBr3 perovskite nanowires is briefly introduced. The comparison of lasing thresholds in CW perovskite lasers is made and discussed. Finally, the importance of such perovskite CW lasers is emphasized, while a perspective on the potential opportunities and remaining challenges of perovskite‐based CW lasers is proposed. [ABSTRACT FROM AUTHOR]

2D layered halide perovskites have attracted significant attention. Apart from the linear optical properties, it is also intriguing to explore the nonlinear optics of 2D layered halide perovskites and their heterostructures. Previous nonlinear optical (NLO) studies of 2D perovskites primarily focus on the thin films or microplates. Herein, the NLO properties of (n‐C4H9NH3)2PbI4/(n‐C4H9NH3)2(CH3NH3)Pb2I7 heterostructures with centimeter size are systematically studied. The NLO properties can be continuously tuned by changing the thickness. A giant two‐photon absorption (2PA) coefficient up to 44 cm MW−1 is obtained for the heterostructures with a total thickness of 20 µm based on the nonlinear transmittance measurement. Additionally, strong multiphoton‐induced photoluminescence is observed in the heterostructures. It is proposed that the giant 2PA coefficient might arise from the small thickness (≈1 µm) of (n‐C4H9NH3)2(CH3NH3)Pb2I7 layer and possibly the nonradiative energy transfer between the different constituting layers within the heterostructures through an antenna‐like effect. Finally, benefiting from the giant 2PA coefficient, direct detection of 980 nm light is demonstrated with a responsivity of 10−7 A W−1 in the heterostructures. The findings suggest the promising applications of 2D perovskite heterostructures in the infrared photodetection and some other nonlinear absorption related optoelectronic devices. [ABSTRACT FROM AUTHOR]

Plasmonic nanolaser holds great potential in breaking down the diffraction limit of conventional optics to the deep sub‐wavelength regime and in ultrafast lasing dynamics. However, plasmonic laser devices are constrained in practical applications due to their high cost and high thresholds. All‐inorganic cesium lead halide perovskites are promising solutions for their excellent optical gain properties and high emission efficiency. In this work, high‐quality single‐crystalline CsPbBr3 perovskite nanowires (NWs) are synthesized by chemical vapor deposition method. The plasmonic lasing is achieved from the CsPbBr3 nanowire based plasmonic devices with lasing threshold down to ≈6.5 µJ cm−2 at room temperature. The highly polarized emission parallel to nanowire axis and polarization‐sensitive pump response confirm the plasmonic characteristic in these devices. Furthermore, time‐resolved photoluminescence study suggests that the radiative recombination lifetime of CsPbBr3 NW is shortened by a factor of ≈6.14 due to Purcell effect. The lasing threshold of plasmonic device increases along with the nanowire length, indicating greater potential in small size and integration in plasmonic device than its photonic counterparts. The results not only provide a solution to fabricate low‐cost nanowire based plasmonic lasers, but also advocate the prospect of all‐inorganic perovskite nanowires as promising candidates in plasmonic‐based devices. Plasmonic nanolaser holds great potential in breaking down the diffraction limit of conventional optics to deep sub‐wavelength regime. Herein, all‐inorganic CsPbBr3 nanowire based plasmonic lasers are demonstrated at room tempearutre with threshold ≈6.5 µJ cm−2. The lasing threshold of plasmonic device increases along with the nanowire length, indicating greater potential in plasmonic integration device than its photonic couterparts. [ABSTRACT FROM AUTHOR]