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Optical logic gates based on nonlinear optical property of material with ultrafast response speed and excellent computational processing power can break the performance bottleneck of electronic transistors. As one of the layered 2D materials, Ta2NiS5 exhibits high anisotropic mobility, exotic electrical response, and intriguing optical properties. Due to the low-symmetrical crystal structures, it possesses in-plane anisotropic physical properties. The optical absorption information of Ta2NiS5 is investigated by anisotropic linear absorption spectra, femtosecond laser intensity scanning (I-scan), and non-degenerate pump-probe technology. The I-scan results show a distinct maximum of ∼4.9 % saturable absorption (SA) and ∼4 % reverse saturable absorption (RSA) at different polarization directions of the incident laser. And, these unique nonlinear optical (NLO) properties originate from the anisotropic optical transition probability. Furthermore, the novel Ta2NiS5-based all-optical logic gates are proposed by manipulating the NLO absorption processes. And, the all-optical OR and NOR logic gates possess an ultrafast response speed approaching 1.7 THz. Meanwhile, an all-optical information transmission method with higher security and accuracy is achieved, which has promising potential to avoid the disclosure of information. This work provides a new path for designing versatile and novel optical applications based on Ta2NiS5 materials. [ABSTRACT FROM AUTHOR]

Blackbody‐sensitive uncooled infrared photodetectors with ultra‐broadband and ultrafast photoresponse have a profound impact on many areas of modern science and technology. However, it is a big challenge for both traditional photodetectors and emerging low‐dimensional ones to simultaneously have all the above characteristics. Here, this challenge is addressed by establishing a Te/WTe2 heterostructure photodetector. The built‐in field of the heterostructure and the crossing conduction and valence bands of WTe2 jointly result in a high responsivity and a visible‐to‐long‐wavelength‐infrared photoresponse range. The peak responsivity (at the 3.3 µm wavelength) reaches 914 mA W−1 at zero bias and 8.51 A W−1 at 2 V bias. Further, the joint action coupled with the high mobility of Te and WTe2 promotes the 3‐dB bandwidth to 153 kHz. The self‐powered blackbody responsivity and specific detectivity reach 235.7 mA W−1 and 1.1 × 108 cm Hz1/2 W−1, respectively. The former increases to 5.82 A W−1 at 1 V bias. Moreover, this device is polarization‐sensitive with a contrast ratio of 2. This work reveals the potential of the Te/WTe2 heterostructure for high‐performance room‐temperature infrared photodetectors. [ABSTRACT FROM AUTHOR]

All-inorganic cesium lead halide perovskite quantum dots have recently received much attention as promising optoelectronic materials with great luminescent properties and bright application prospect in lighting, lasing, and photodetection. Although notable progress has been achieved in lighting applications based on such media, the performance could still be improved. Here, we demonstrate that the light emission from the perovskite QDs that possess high intrinsic luminous efficiency can be greatly enhanced by using metallic thin films, a technique that was usually considered only useful for improving the emission of materials with low intrinsic quantum efficiency. Eleven-fold maximal PL enhancement is observed with respect to the emission of perovskite QDs on the bare dielectric substrate. We explore this remarkable enhancement of the light emission originating from the joint effects of enhancing the incident photonic absorption of QDs at the excitation wavelength by means of the zero-order optical asymmetric Fabry–Perot-like thin film interference and increasing the radiative rate and quantum efficiency at the emission wavelength mediated by surface plasmon polaritons. We believe that our approach is also potentially valuable for the enhancement of light emission of other fluorescent media with high intrinsic quantum efficiency.

The on‐chip near‐infrared (NIR) lasing devices based on van der Waals (vdW) layered materials are highly desired owing to their widespread applications in optoelectronic communication, computing, and sensing. However, the single‐mode NIR lasing devices with superior performance based on vdW layered materials are hard to obtain because of complex and meticulous microcavity structure and the damage to layered materials during preparation. Here, a high‐quality NIR single‐mode lasing device in γ‐phase indium selenide (γ‐InSe) is achieved by using a transferrable planar microcavity. The single‐mode lasing devices based on distributed Bragg reflectors microcavity and super Tamm structure can be simply prepared with quality factors up to 5710 and 3526, respectively. And angle‐resolved spectra show that the lasing device has high directionality with divergence angle <5°. Moreover, the wavelength of lasing device can be tuned ≈30 nm by varying the cavity length via thickness control of γ‐InSe layer. These results not only suggest that γ‐InSe is a promising material for NIR lasing devices, but also present a simple and effective approach for preparing high‐quality lasing devices utilizing other vdW layered materials. [ABSTRACT FROM AUTHOR]

Integrated multiwavelength nanolasers are important in the practical development of optical circuitry for optical information processing and optical data storage. Herein, a new method for on‐chip integrated lasers is proposed, which can integrate single‐mode lasers with multiple wavelengths at room temperature. A four‐wavelength single‐mode nanoribbon laser chip is fabricated for demonstration. The mode of different laser units is controlled by the thickness of dielectric microcavity layers to select the resonant modes of excitation. Therefore, multiwavelength lasing can be coupled out based on the integrated cavity which is realized using combinatorial etching technique and can integrate tens of different‐wavelength lasers on a chip. The lasing modes of this device are all single‐mode lasing because of the short cavity length. Its lowest lasing threshold is only 5.4 kW cm−2. The gain material and the dielectric microcavity can be controlled and fabricated separately, which have strong controllability and flexibility. This new laser chip paves the way for a new class of hybrid nanolasers for chip‐integrated applications. [ABSTRACT FROM AUTHOR]

The layer-by-layer buildup of a two-dimensional transition metal dichalcogenide monolayer to form a stack is an important development for these materials, which performs many remarkable properties in the light–matter interaction. Herein, we find clear evidence of exciton–polaritons emerging from WS2/hBN/WS2 heterostructures embedded in a dielectric microcavity under optical pumping. A large Rabi splitting of 15 meV is observed at room temperature, which increases to 25 meV at 5 K. An all-dielectric Fabry–Pérot microcavity provides a simple but effective way to study the room temperature strong coupling between cavity photons and excitons. Our results pave the way for room-temperature polaritonic devices based on quantum-well van der Waals heterostructures. [ABSTRACT FROM AUTHOR]

Inorganic perovskites have become a widely investigated candidate for fabrication of high‐performance micro‐devices due to their excellent optoelectronic properties and stability to the environment. Especially, their excellent lasing characteristics as a micro/nanolaser source, combined with flexible substrates, have great potential in the field of wearable or foldable photonic device applications. Here, the high‐quality CsPbBr3 perovskite microsheets with stress‐induced grooves are directly prepared on the ultrathin fluorine mica by the chemical vapor deposition method, and the single‐mode lasers are realized in these large‐size (>15 × 15 µm) microsheets. Thanks to the flexibility of mica, bending induced tensile strain on CsPbBr3 microsheet causes the laser mode blueshift continuously and reversibly with 15.3 meV %−1, this can be well explained by the Lorentz oscillator model under lasing conditions. Furthermore, by using the first‐principles calculation, it is clarified that the bandedge blueshift originates from the distortion of {PbBr6}4− octahedra and the consequential increase of the bond length of Pb‐Br3 and the Pb‐Br3‐Pb bond angle. This work opens up a new way to realize on‐chip single‐mode lasers with microstructures, and is helpful for the application of flexible photonic device in the fields of integrated on‐chip sensors. [ABSTRACT FROM AUTHOR]

Low-threshold single-mode laser in CsPbBr3 microdiscs grown between two distributed Bragg reflectors (DBRs) is realized at room temperature. The CsPbBr3 microdiscs are directly synthesized on the surface of prepared first-half DBRs microcavity by a chemical vapor deposition method. This scheme avoids possible surface damage or contamination caused by the traditional transfer of sample into the DBRs. The single-mode laser with low threshold (∼1.3 μJ/cm2) was obtained in the CsPbBr3 microdiscs sandwiched in DBRs and measured by using the micro-photoluminescence spectroscopy. The length of the resonant cavity is short enough to support a large free spectral range, which ensures only one mode in the bandwidth of the optical gain. Moreover, by modulating the thickness of the CsPbBr3 microdiscs, the wavelength of single-mode laser emission can be broadly tuned from 529.6 to 544.1 nm. This work provides a method of fabricating single-mode laser in DBRs, which may have potential applications in on-chip integration of optoelectronic devices and signal processing. [ABSTRACT FROM AUTHOR]

The effect of adsorbed adatoms on the structural stability and electronic properties of monolayer N2P6 have been systematically studied via first-principles simulation methods. It is found that pristine N2P6 is an indirect 0.21 eV band gap semiconductor, with a pleated honeycomb-like structure similar to phosphorene. The calculation results show that adsorbed adatoms can modify the properties of monolayer N2P6 effectively. The degree of local distortion strongly depends on the electronegativity and size of adatoms, also the adsorption energy ranges from 0.3 to 5.8 eV depending on the species of adatoms. The electronic properties show metallic behavior with several adsorbed metal atoms (Li, Na, Al, K, Cu, Ni, and Zn) and some non-metal atoms (H, F, P, and Cl), while adsorbed O, S, Ca, and Si atoms still remain semiconductors. The systems of Ni and Zn adatoms show ferromagnetic behavior, and adsorbed Mg exhibits a half-metallic character. Our theoretical studies indicate that N2P6 possesses potential application in the field of gas sensors. [ABSTRACT FROM AUTHOR]

All-inorganic cesium lead halide perovskite quantum dots have recently received much attention as promising optoelectronic materials with great luminescent properties and bright application prospect in lighting, lasing, and photodetection. Although notable progress has been achieved in lighting applications based on such media, the performance could still be improved. Here, we demonstrate that the light emission from the perovskite QDs that possess high intrinsic luminous efficiency can be greatly enhanced by using metallic thin films, a technique that was usually considered only useful for improving the emission of materials with low intrinsic quantum efficiency. Eleven-fold maximal PL enhancement is observed with respect to the emission of perovskite QDs on the bare dielectric substrate. We explore this remarkable enhancement of the light emission originating from the joint effects of enhancing the incident photonic absorption of QDs at the excitation wavelength by means of the zero-order optical asymmetric Fabry–Perot-like thin film interference and increasing the radiative rate and quantum efficiency at the emission wavelength mediated by surface plasmon polaritons. We believe that our approach is also potentially valuable for the enhancement of light emission of other fluorescent media with high intrinsic quantum efficiency. [ABSTRACT FROM AUTHOR]

Semiconductor nanostructures such as nanowires and nanoribbons have shown great potential for fabrication of functional nanoscale lasers due to their high dielectric contrast and bandgap engineering performance. However, these as-grown nanostructures are weak in structural controllability, and the operation of highly desired single-mode lasers currently performed by coupled nanostructural cavities needs a relatively complex fabrication process and lacks flexibility. In this work, a tunable coupled nanoribbon cavity was simply obtained by using a home-made transfer platform. Relying on this, the Vernier effect-driven high performed single-mode laser was realized. Most interestingly, the laser mode can be reversibly tuned between single-mode and multi-mode by adjusting the gap of two coupled nanoribbons. The coupling constant and the optical loss of different gaps were demonstrated by simulation, large diffraction loss, and scattering loss as limiting factors for coupling were clarified. This work offers an alternative route toward realizing mode-tunable nanoscale lasers, which may have great potential in flexible multi-functional optoelectronic devices. [ABSTRACT FROM AUTHOR]

Indium antimony is a direct, narrow bandgap III–V semiconductor with ultrahigh carrier mobility and an attractive optoelectronic device candidate for use in the visible to infrared region. Here, an infrared (IR) photodetector based on high‐quality InSb nanosheets (NSs) is presented, which shows a clear photoresponse over a broad spectral range from visible (637 nm) to infrared (4.3 µm). Due to the high surface‐to‐volume ratio of nanostructured materials, defects on the sample surface can affect performance, which is a disadvantage for the ambipolar InSb photodetectors. To eliminate the impact of sample surface defects on performance, the surface of the sample is passivated with a ferroelectric film and the mechanism of increased sensitivity is explored. After covering the protective layer, the performance of the detector is greatly improved. The responsivity and detectivity of the photodetector are 311.5 AW−1 and 9.8 × 109 Jones, respectively. Compared with devices before passivation, the dark current is two orders of magnitude lower, the responsivity is 20 times higher, and the photoresponse time is shortened from seconds to the order of milliseconds. These InSb NSs with their outstanding photoelectric properties have great potential for developing next‐generation nanoscale optoelectronic devices. [ABSTRACT FROM AUTHOR]

Semiconductor nanowires/nanoribbons have great potential in nanoscale lasers because of their intrinsic laser capabilities and excellent optoelectronic properties. However, these as-grown nanostructures, lacking precise structural controllability, usually show multimode lasing, which hinders their applications in on-chip functional optoelectronic devices. In this work, by using a home-made strain apparatus, we obtained out-of-plane buckled cadmium selenide nanoribbons, resulting in a single-mode lasing at the curved part of the nanoribbons. Taking into consideration the bending structure of nanoribbons, we speculate that deformation-induced light confinement and strain-driven carrier's redistribution contributed mainly to the single-mode lasing. Moreover, a periodic out-of-plane bending of nanoribbons is realized by thermal controlling deformation of the elastic substrate and cadmium selenide, in which single-mode lasing at each crest part can be obtained. Our work opened an alternative avenue to realize nanoscale single-mode lasers, which was quite useful for flexible optoelectronic devices. [ABSTRACT FROM AUTHOR]

Cavity polaritons, originating from the strong coupling effect between cavity modes and excitons, have been tremendously investigated because of their high potential in new or quantum optoelectronic devices. Among them, realization of their dynamic controllability is highly desirable for real applications. In this work, we present a dynamic modulation of cavity polaritons via strain-engineering in the ZnO whispering gallery microcavity. By using a home-made strain apparatus, a nearly uniaxial stress is precisely applied to ZnO microwires, thus inducing an internal strain along its c-axis. Dynamic tuning of cavity polariton modes is clearly characterized by angle-resolved microphotoluminescence spectroscopy. The coupled oscillator's model with fitting parameters of strain-dependent excitons' energies can well describe the modes' redshift. Moreover, we show that the modes' redshift can also be understood by the strain-induced refractive index increase, described by the Lorentz model, of which the underlying mechanism is also related to light-exciton strong coupling. Finally, the strain-engineered dynamic tuning of polariton lasing modes is demonstrated as well, and this actually provides convincing evidence for the polariton states surviving above the threshold. This work indicates that strain-engineered cavity polaritons would pave an alternative way for developing polariton-based integrated or flexible optoelectronic devices. [ABSTRACT FROM AUTHOR]

Rubidium lead halides (RbPbX3), an important class of all‐inorganic metal halide perovskites, are attracting increasing attention for photovoltaic applications. However, limited by its lower Goldschmidt tolerance factor t≈0.78, all‐inorganic RbPbBr3 has not been reported. Now, the crystal structure, X‐ray diffraction (XRD) pattern, and band structure of perovskite‐phase RbPbBr3 has now been investigated. Perovskite‐phase RbPbBr3 is unstable at room temperature and transforms to photoluminescence (PL)‐inactive non‐perovskite. The structural evolution and mechanism of the perovskite–non‐perovskite phase transition were clarified in RbPbBr3. Experimentally, perovskite‐phase RbPbBr3 was realized through a dual‐source chemical vapor deposition and annealing process. These perovskite‐phase microspheres showed strong PL emission at about 464 nm. This new perovskite can serve as a gain medium and microcavity to achieve broadband (475–540 nm) single‐mode lasing with a high Q of about 2100. [ABSTRACT FROM AUTHOR]

We systematically compare the active and the passive methods for infrared scattering-type scanning near-field optical microscopy (s-SNOM). The active SNOM makes use of IR lasers or incoherent thermal emitters to illuminate a sample, whereas the passive method directly measures extremely weak fluctuating electromagnetic evanescent fields spontaneously generated at the sample surface without any external illumination. For this reason, our specific version of the passive SNOM is called a scanning noise microscope (SNoiM). In thermal equilibrium, the two methods are shown to be similar, both mapping the nanoscale variation of the complex dielectric constant of the sample. We demonstrate that a significant difference between the two methods emerges when the sample is driven out of thermal equilibrium, viz., the active SNOM is insensitive whereas the SNoiM is extremely sensitive to the electron temperature in locally heated nanoregions. [ABSTRACT FROM AUTHOR]

Obtaining single-mode lasing with excellent stability and beam quality is highly desirable but still challenging. Although microplatelet optical cavities attract great attention because of their important lasing characteristics of directionality and high-power output light, they suffer from weak light confinement, which restricts applications of a single-mode laser. Herein, we increased the vertical thickness of the microplatelet cavity appropriately to achieve 3D light confinement in a CsPbBr3 micro-cubic cavity, from which single-mode lasing with an extreme narrow linewidth of 0.064 nm (Q∼ 8500) was successfully achieved at room temperature. Besides, the microcavity we prepared exhibits superb capability for the output of continuous stable single-mode lasing. Different growth stages of cavities were found and a related growth mechanism was analyzed, indicating that the micro-cubic cavities evolved from nanospheres. Moreover, interesting multi-mode lasing spectra with higher-order transvers modes were observed in larger micro-cubic cavities. All these results suggest that 3D CsPbBr3 micro-cubic cavities, which provide improved photo-physical properties, are important for fundamental studies and future applications in photonic devices. [ABSTRACT FROM AUTHOR]

The band-edge emission lifetime in a single ZnO tetrapod is studied by using the time-resolved confocal micro-photoluminescence (TR- μ PL) spectroscopic technique at room temperature. By performing μ PL and TR- μ PL mapping along the tapered arm of tetrapod, we observe whispering gallery mode (WGM) polaritons and find that the predominant radiative lifetime of exciton polaritons decreases linearly with increasing the surface-to-volume ratio of the sample. This behavior is ascribed to the surface electric field induced enhancement of the radiative decay rate of the exciton-like polaritons coupling with LO phonons. [ABSTRACT FROM AUTHOR]

Semiconductor nanostructuressuch as nanowires and nanoribbonsfunctioning as Fabry–Pérot (F-P)-type optical cavitiesand nanolasers have attracted great interest not only for their potentialuse in nanophotonic systems but also to understand the physics oflight–matter interactions at the nanoscale. Due to their nanoscaledimensions, new techniques need to be continuously developed to characterizethe nature of highly confined optical modes. Furthermore, the inadequacyof typical far-field photoluminescence experiments for characterizingthe nanoscale cavity modes such as parity and order has precludedefforts to obtain precise information that is required to fully understandthese cavities. Here, we utilize a modified Young’s interferencemethod based on angle-resolved microphotoluminescence spectral techniqueto directly reveal the parity of F-P cavity modes in CdS nanostructuresfunctioning as waveguides and nanolasers. From these analyses, themode order can be straightforwardly obtained with the help of numericalsimulations. Moreover, we show that the Young’s technique isa general technique applicable to any F-P type cavities in nanoribbons,nanowires, or other photonic and plasmonic nanostructures. [ABSTRACT FROM AUTHOR]

A hybrid plasmonic–photonic crystal consisting of a low-cost metal (Al or Cu) covered by self-assembly polystyrene sub-micro sphere arrays is fabricated. The angle-resolved reflection spectra show the existence of propagating optical surface modes in the structure. Especially, under normal incidence, five surface modes can be observed clearly. With the help of theoretical calculation, the origin of surface resonance modes is confirmed. From both the experiment and simulation, the surface plasmon modes supported by this structure possess high Q factors, which are comparable with those of the modes based on noble metals. Moreover, with a dielectric layer deposited on the top of the structure, its potential application for surface plasma polariton sensors is proposed. [ABSTRACT FROM AUTHOR]

Strainengineering can be utilized to tune the fundamental properties ofsemiconductor materials for applications in advanced electronic andphotonic devices. Recently, the effects of large strain on the propertiesof nanostructures are being intensely investigated to further expandour insights into the physics and applications of such materials.In this Letter, we present results on controllable buckled cadmium-sulfide(CdS) optical nanowires (NWs), which show extremely large energy bandgaptuning by >250 meV with applied strains within the elastic deformationlimit. Polarization and spatially resolved optical measurements revealcharacteristics related to both compressive and tensile regimes, whilemicroreflectancespectroscopy clearly demonstrates the effect of strain on the differenttypes of excitons in CdS. Our results may enable strained NWs-basedoptoelectronic devices with tunable optical responses. [ABSTRACT FROM AUTHOR]

A robust exciton-polariton effect in a ZnO whispering gallery microcavity well above room temperature is presented. The lower polariton branches are tuned by current induced thermal effect. The red shift can be as large as ∼40 meV. It is found that the strong coupling can be preserved and the polariton-phonon interaction quenching effect remains up to ∼550 K, while the Rabi splitting is about 330 meV. The tuning speed is in the order of millisecond, showing its potential in polariton-based optoelectronic device application. [ABSTRACT FROM AUTHOR]

Due to the extraordinary chemical and physical properties, ternary chalcogenides with wide‐range bandgap, unique structures, and exceptional photoelectric properties have attracted great interest recently. Among them, Chromium thiophosphate (CrPS4) is a promising semiconductor with excellent optical, mechanical, and electronic properties and has a lower lattice symmetry resulting in significant in‐plane anisotropy. Here, the polarization‐dependent nonlinear optical (NLO) responses of CrPS4 flake are investigated. Based on polarization‐resolved Raman spectroscopy, which identifies the crystal axis of sample, the anisotropic linear absorption spectra, I‐scan technique, and pump‐probe measurements are utilized to investigate the optical absorption information of CrPS4. The polarization‐dependent NLO responses are found originating from the anisotropic optical transition probability. And the polar optical phonons play an important role in carrier relaxation processes. Furthermore, CrPS4‐based all‐optical switches are proposed, which can modulate the transmittance of signal light (CW laser) by changing the polarization of switch light (fs laser). This work provides insights into polarization‐dependent CrPS4‐based devices, which is important to promote the potential applications in optical modulator, versatile optoelectronic detection, and so on. [ABSTRACT FROM AUTHOR]

High-quality In2O3 polyhedrons with different morphologies were fabricated and studied as vertical Fabry-Pérot (FP) microcavities. By using the microphotoluminescence technique, we identified a series of FP resonant modes in such systems, whose energies lie in the visible spectral range and are scalable with the cavity size. Experimental results are in good agreement with full-wave numerical simulations and can be well fitted with a plane wave interference model. Compared with the conventional one dimensional nanowire/nanobelt FP cavities, such vertical FP microcavities have much less optical loss and provide efficient optical modulations, which may find many applications in developing optical devices. [ABSTRACT FROM AUTHOR]

Nearly perfect In2O3 octahedra were fabricated and studied as optical resonators. Electron microscopy images revealed that the octahedra have single-crystal structures, very smooth surfaces, and regular geometric morphologies. Bow-tielike modes in the visible spectral range were clearly observed at room temperature by using the spatially resolved spectroscopic technique. The experimental observations are described and fitted well with the plane wave interference model and Cauchy dispersion formula for refractive indices. [ABSTRACT FROM AUTHOR]

We report on the use of In2O3 nanowires with hexagonal cross section as optical whispering gallery resonators. The single-crystal In2O3 nanowires were fabricated by an in situ thermal oxidation method. Whispering gallery modes (WGMs) in the visible spectral range were directly observed at room temperature. Due to the slight tapering of the nanowires, the energies and orders of the WGMs were modulated when excitations were scanned along the c-axis (length) of the nanowires. The experimental results were explained and fitted well with a plane wave interference model and Cauchy dispersion formula for refractive indices. [ABSTRACT FROM AUTHOR]

Nanoscale selected‐area chemical engineering is challenging but critical to manipulate carrier transport and realize multifunctional characteristics in advanced devices. Undesired chemical contaminants might occur in conventional lithographic processes and would degrade the characteristics of chemical‐sensitive vanadium oxide nanostructures. Here, a facile strategy is introduced to chemically engineer VO2 nanostructures using a nonlithographic direct‐writing process without chemical reagents and sacrificial layers. Nanoscale selected‐area photooxidation promotes the formation of VO2+x patterns in VO2 nanostructures. Selected‐area chemical nanoengineering allows direct designing and engineering of correlated vanadium oxides for controllable Mott field‐effect transistors and memory devices. A nonlithographic strategy for selected‐area chemical nanoengineering (SACNE) of correlated functional vanadium dioxide (VO2) nanostructures without any chemical reagents and sacrificial layers is demonstrated. Nanoscale selected‐area photooxidation promotes the formation of VO2+x alternative patterns in VO2 nanostructures during a nonlithographic direct‐writing process. The SACNE allows direct engineering correlated vanadium oxides at the nanoscale. [ABSTRACT FROM AUTHOR]

The realization of ultrahigh quality upconverted single‐mode lasing in wavelength‐scale cavity is still a great challenge, because of limitation of microcavity quality, gain medium, and low spontaneous emission coupling efficiency β. In this work, it is demonstrated that inorganic cesium lead bromide (CsPbBr3) perovskite spheres with size of ≈780 nm serve as a gain medium and whispering‐gallery cavity simultaneously for two‐photon excited single‐mode laser. Lasing mode with a very narrow linewidth (≈0.037 nm) is realized, corresponding to an ultrahigh Q factor ≈1.5 × 104. Surprisingly, the lasing performance of such small microcavity is best among reported naturally formed semiconductor microcavities. Furthermore, room‐temperature single‐mode lasing at same wavelength can be obtained at any angle between −30° and 30°, showing the nearly uniform emission output of the spherical microcavity. This work paves a simple and straight way to obtain ultrahigh Q two‐photon excited single‐mode lasing in micro/nanostructures, holding great promise for practical applications in frequency upconversion, high sensitive sensing in nano‐optics. Ultrahigh quality upconverted single‐mode lasers in individual all‐inorganic CsPbBr3 sub‐micrometer spherical whispering‐gallery mode microcavities are realized. The upconverted single‐mode laser exhibits ultrahigh Q factor (≈1.5 × 104) and very small linewidth (≈0.037 nm) in such a sub‐micrometer spherical (D < 1 µm) cavity, which is the best in all the reported natural nano/microcavity lasers. [ABSTRACT FROM AUTHOR]

The development of novel approaches that control absorption and emission operating in the long wavelength infrared (LWIR) spectral region is of fundamental importance for many applications, such as remote temperature sensing, thermal imaging, radiation cooling, environmental monitoring, and night vision. A high performance plasmonic metasurface–based absorber for the LWIR spectral region is presented. In the design, a pyroelectric thin film, poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) copolymer, is introduced as spacer, that offers the device not only multiple selective high absorption bands but also promising potential for application in optoelectronics. The angle‐resolved optical responses show that the absorption effect is sensitive to the incident angles and can be controlled by the periodicity, indicating that the design can function as optical devices with directional and frequency‐selective absorption/emission characteristics. By employing near‐field optical microscopy, both the near‐field amplitude and phase optical responses of the absorber are investigated at resonant wavelength, thereby providing direct experimental evidence to verify the nature of the absorption effect. To further demonstrate the versatility of the design, a particular metasurface patterned by the building blocks of the absorber is fabricated. 2D hyperspectral images show that such a patterned structure exhibits both frequency and spatially selective absorption. A high performance plasmonic metasurface–based absorber for the long wavelength infrared spectral region, is presented which possesses multiple selective high absorption bands. Patterned by the building blocks of the absorber, a spatial and frequency varying absorption metasurface is also experimentally demonstrated. The design has various applications including thermal infrared light sources, thermal management, uncooled infrared photodetectors, and hyperspectral thermal imaging. [ABSTRACT FROM AUTHOR]

Phonon properties of boron nitride nanotubes (BNNTs) were investigated using Raman spectroscopy at different temperatures and new sp3-bonded BN vibrations were identified. The Raman peak of the mode of BNNTs is found to be downshifted and broadened compared to that of hexagonal BN at the same temperature. By increasing the temperature, the energy of the mode and the sp3-bonding mode are downshifted, with the temperature coefficients being −0.010 and −0.069 cm−1/K, respectively. We attribute this downshifting to anharmonic effects as well as the elongation of the B–N bond in BNNT structures with increasing temperature. [ABSTRACT FROM AUTHOR]

We demonstrate a novel way to realize room-temperature polariton parametric scattering in a one-dimensional ZnO microcavity. The polariton parametric scattering is driven by a polariton condensate, with a balanced polariton pair generated at the adjacent polariton mode. This parametric scattering is experimentally investigated by the angle-resolved photoluminescence spectroscopy technique under different pump powers and it is well described by the rate equation of interacting bosons. The direct relation between the intensity of the scattered polariton signal and that of the polariton reservoir is acquired under nonresonant excitation, exhibiting the explicit nonlinear characteristic of this room-temperature polariton parametric process. [ABSTRACT FROM AUTHOR]