Rydberg State Single-Mode Polariton Lasing with Ultralow Threshold via Symmetry Engineering.

Symmetry plays an essential role in the fundamental properties of a physical system. In this work, we report on the realization of tunable single-mode polariton lasing from highly excited Rydberg states via symmetry engineering. By breaking the symmetry of the polaritonic wave function through potential wells and controlling the spatial overlap between the gain region and the eigen mode, we are able to generate single-mode polariton lasing, reversibly and dynamically, from quantized polariton states. Increasing the asymmetry of the potential well, single-mode lasing can be achieved even for the highly excited Rydberg state with a principle quantum number of N = 14. Moreover, as a result of the excellent reservoir-eigen mode overlap and efficient spatial confinement, the threshold of lasing can be reduced up to 6 orders of magnitude, compared with those conventional pumping schemes. Our results present a new strategy toward the realization of thresholdless polariton lasing with dynamical tunability.

Improving the data rate for long distance visible light communication using h-BN/CdZnSeS@ZnSeS quantum dot composite.

Quantum dots (QDs) are exploited in visible light communication (VLC) due to their unique optical properties. However, it is still a challenge to conquer heating generation and photobleaching under prolonged illumination. In this paper, we proposed to utilize hexagonal boron nitride (h-BN) nanoplates to improve the thermal stability and photo stability of QDs and long-distance VLC data rate. After heating to 373 K and cooling to the initial temperature, photoluminescence (PL) emission intensity recovers to 62% of the original intensity and after 33 hours of illumination, PL emission intensity still maintains 80% of the initial intensity, while that of the bare QDs is only 34% and 53%, respectively. The QDs/h-BN composites perform a maximum achievable data rate of 98 Mbit/s by applying on-off keying (OOK) modulation, while the bare QDs are only 78 Mbps. In the process of extending the transmission distance from 0.3 m to 5 m, the QDs/h-BN composites exhibit superior luminosity corresponding to higher transmission data rates than bare QDs. Particularly, when the transmission distance reaches 5 m, the QDs/h-BN composites still show a clear eye diagram at a transmission rate of 50 Mbps while the eye diagram of bare QDs is indistinguishable at 25 Mbps. During 50 hours of continuous illumination, the QDs/h-BN composites keep a relatively stable bit error rate (BER) at 80 Mbps while that of QDs continuously increase, and the -3 dB bandwidth of QDs/h-BN composites keep around10 MHz while the bare QDs decrease from 12.6 MHz to 8.5 MHz. After illumination, the QDs/h-BN composites still indicate a clear eye diagram at a data rate of 50 Mbps while that of pure QDs is indistinguishable. Our results provide a feasible solution for realizing an enhanced transmission performance of QDs in longer-distance VLC.

Efficient removal of uranium (VI) from water by a hyper-cross-linked polymer adsorbent modified with polyethylenimine via phosphoramidate linkers.

Practical adsorbents with high efficiency are essential to effectively treating wastewater. Herein, a novel porous uranium adsorbent (PA-HCP) having a considerable amount of amine and phosphoryl groups was designed and synthesized by grafting polyethyleneimine (PEI) on a hyper-cross-linked fluorene-9-bisphenol skeleton via phosphoramidate linkers. Furthermore, it was used to treat uranium contamination in the environment. PA-HCP exhibited a large specific surface area (up to 124 m2/g) and a pore diameter of 2.5 nm. Batch uranium adsorptions on PA-HCP were investigated methodically. PA-HCP demonstrated a uranium sorption capacity of >300 mg/g in the pH range of 4-10 (C0 = 60 mg/L, T = 298.15 K), with its maximum capacity reaching 573.51 mg/g at pH = 7. The uranium sorption process obeyed the pseudo-second-order model and fitted well with the Langmuir isothermal. In the thermodynamic experiments, uranium sorption on PA-HCP was revealed to be an endothermic, spontaneous process. Even in the presence of competing metal ions, PA-HCP exhibited excellent sorption selectivity for uranium. Additionally, excellent recyclability can be achieved after six cycles. Based on FT-IR and XPS measurements, both the PO and -NH2 (and/or -NH-) groups on PA-HCP contributed to efficient uranium adsorption as a result of the strong coordination between these groups and uranium. Furthermore, the high hydrophilicity of the grafted PEI improved the dispersion of the adsorbents in water and facilitated uranium sorption. These findings suggest that PA-HCP can be used as an efficient and economical sorbent to remove U(VI) from wastewater.

Relaxation Oscillations of an Exciton-Polariton Condensate Driven by Parametric Scattering.

We report the observation of coherent oscillations in the relaxation dynamics of an exciton-polariton condensate that were driven by parametric scattering processes. As a result of the interbranch scattering scheme and the nonlinear polariton-polariton interactions, such parametric scatterings exhibit a high scattering efficiency that leads to the fast depletion of the polariton condensate and the periodic shut-off of the bosonic stimulation processes, eventually causing relaxation oscillations. Employing polariton-reservoir interactions, the oscillation dynamics in the time domain can be projected onto the energy space. In theory, our simulations using the open-dissipative Gross-Pitaevskii equation are in excellent agreement with experimental observations. Surprisingly, the oscillation patterns, including many excitation pulses, are clearly visible in our time-integrated images, implying the high stability of the relaxation oscillations driven by polariton parametric scatterings.

Femtosecond Dynamics of a Polariton Bosonic Cascade at Room Temperature.

Whispering gallery modes in a microwire are characterized by a nearly equidistant energy spectrum. In the strong exciton-photon coupling regime, this system represents a bosonic cascade: a ladder of discrete energy levels that sustains stimulated transitions between neighboring steps. Here, by using a femtosecond angle-resolved spectroscopic imaging technique, the ultrafast dynamics of polaritons in a bosonic cascade based on a one-dimensional ZnO whispering gallery microcavity are explicitly visualized. Clear ladder-form build-up processes from higher to lower energy branches of the polariton condensates are observed, which are well reproduced by modeling using rate equations. Remarkably, a pronounced superbunching feature, which could serve as solid evidence for bosonic cascades, is demonstrated by the measured second-order time correlation factor. In addition, the nonlinear polariton parametric scattering dynamics on a time scale of hundreds of femtoseconds are revealed. Our understandings pave the way toward ultrafast coherent control of polaritons at room temperature.

Fabry-Perot resonance-suppressed double-layer metal mesh window for electromagnetic interference shielding.

Traditional electromagnetic interference shielding windows that can simultaneously reflect microwaves and transmit visible light are usually fabricated by depositing one metal mesh layer on the surface of the window. However, such a structure always suffers from strong Fabry-Perot resonance (FPR), which leads to the decline of shielding effectiveness (SE). Here, we analyze the mechanism of FPR from a perspective of the equivalent circuit model and further report a facile approach to minimize the FPR by depositing another high-resistance mesh layer on the back side of the shielding window, which can greatly reduce reflected waves, ensuring that interference cannot be formed. Simulation results prove that FPR can be effectively eliminated by the proposed method, and experiments further show that for a shielding window made with Schott B270 glass plate, the SE can be enhanced by 6.3 dB (76.6% energy attenuation) at declining points, while transmittance is only reduced by 1.6%.

A miniaturized analytical method based on molecularly imprinted absorbents for selective extraction of (S)-1,1'-binaphthyl-2,2'-diamine and combinatorial screening of polymer precursors by computational simulation.

Chiral resolution of binaphthylamine is often a toilful conundrum in the field of analytical chemistry and biomedicine. The work puts forward a selective, sensitive, and miniaturized analytical method based on molecularly imprinted polymers (MIPs) as adsorbent for miniaturized tip solid-phase extraction (MTSPE) in the separation of binaphthylamine enantiomer. This method combines the advantages of MIPs (high selectivity), MTSPE (low consumption), and high-performance liquid chromatography (HPLC, high sensitivity). A simple synthesis methodology of MIP (P2) was conducted through bulk polymerization with (S)-(-)-1,1'-binaphthyl-2,2'-diamine (S-DABN) as template together with methacrylic acid monomer, and ethylene glycol dimethacrylate as cross-linker in proper porogen, realizing a selective recognition and efficient enrichment for S-DABN. The method exhibited appreciable linearity (0.06-1.00 mg ml-1 ), low quantification limit (0.056 mg ml-1 ), good absolute recoveries (45.70%-69.29%), and high precision (relative standard deviations ≤ 3.54%), along with low consumption (0.50 ml sample solution and 25.0 mg adsorbent). Based on the density functional theory, computational simulation was used to make a preliminary prediction for rational design of MIPs and gave a reasonable elaboration involving the potential mechanism of templates interacting with functional monomers. The adsorption kinetics and thermodynamics were investigated to evaluate the recombination process of substrates. In addition, the selectivity of MIPs for S-DABN was obtained by MIP-MTSPE coupled with HPLC, which supports the feasibility of this convenient design process. The proposed method was employed for selective extraction of S-DABN and exhibited promising potential in the application of chiral analysis.

Transparent ultra-wideband double-resonance-layer metamaterial absorber designed by a semiempirical optimization method.

In this study, a transparent ultra-wideband double-resonance-layer absorber was designed using a semiempirical optimization method. In this method, an equivalent circuit model, genetic algorithm, and parameter fitting are employed to reduce the computation time and improve the design flexibility. Simulations and measurements show that the as-designed absorber can achieve ultrawide microwave absorption in the range of 2.00 to 11.37 GHz with a fractional bandwidth of 140.2%. Furthermore, electric field and surface current distributions show that the broad bandwidth was derived from the good matching of the absorption peaks in the two resonance layers. In addition, the target waveband of the as-designed absorber covered the wavebands of WiFi and radio-frequency identification, as well as part of the 5G waveband. This makes the proposed absorber a good candidate for daily electromagnetic pollution reduction.

Antimicrobial and antitumor activity of peptidomimetics synthesized from amino acids.

Thirteen cationic peptidomimetics derived from amino acids bearing an alkyl or ethynylphenyl moiety that mimic the structure of cationic antibacterial peptides were designed and synthesized using a simple coupling reaction of an amino acid with a substituted amine. Antibacterial activities of the resulting peptidomimetics against drug-sensitive bacteria, such as Gram-positive Staphylococcus aureus (S. aureus) and Bacillus subtilis, Gram-negative Escherichia coli (E. coli) and Salmonella enterica, and a drug-resistant bacterium, methicillin-resistant S. aureus (MRSA), were systematically evaluated. Most peptidomimetics show significant broad-spectrum antibacterial activity. A-L-Iso-C12 (isoleucine derivative bearing a dodecyl moiety) show MICs of 2.5 µg/mL against S. aureus and 4 µg/mL against MRSA and A-L-Val-C12 (valine derivative bearing a dodecyl moiety) show MICs of 1.67 µg/mL against E. coli and 8.3 µg/mL against MRSA. A-L-Val-C12 showed low cytotoxicity toward L929 cells in comparison with SGC 7901 cells, indicating tumor-directed killing by peptidomimetics while avoiding toxicity to normal cells. The influences of type of amino acid and substituent, length of substituent, and stereochemistry of amino acids on antibacterial activity and cytotoxicity of peptidomimetics were systematically investigated. The results indicate that this series of cationic peptidomimetics derived from amino acids display antitumor activity and may be useful for treatment of bacterial infections.

Polariton-Polariton Interactions Revealed in a One-dimensional Whispering Gallery Microcavity.

Coulomb interactions are essential to the dynamics and optical properties of exciton-polaritons. Here, we report an experimental observation of polariton-polariton interactions far beyond theory in a one-dimensional whispering gallery microcavity. Based on the unique half-light half-matter nature, we were able to clarify the effects of excitons, quantum confinement, and nonthermalized polariton distribution in the measurements of the polaritonic interactions. Spectacularly, our position-scan and power-scan investigations both revealed that the polariton-polariton interaction strength is up to 2 orders of magnitude larger than theoretical predictions. These results suggest that polaritonic interactions are far more complicated than the expectation and should be re-examined in polariton physics and devices involving polaritonic interactions.

High-performance broadband electromagnetic interference shielding optical window based on a metamaterial absorber.

An excellently transparent metamaterial-based electromagnetic interference (EMI) shielding window with broadband absorption is presented theoretically and demonstrated experimentally. The window is composed of double split circular ring (SCR) elements whose absorption spectra feature two mild resonant peaks. Indium-tin-oxide (ITO) with resonant patterns is utilized as the material to induce high ohmic loss and broaden the absorption bandwidth. The window achieves strong absorptivity, > 90%, covering an ultrawide frequency range of 7.8-18.0 GHz. Moreover, the measured shielding effectiveness (SE) of the window is > 18.25 dB, at 7.0-18.0 GHz, while the average optical transmittance is fixed at ∼73.10% in the visible-near-infrared (Vis-NIR) region of 400-1,500 nm. Further, the absorption mechanism is revealed by designing an equivalent circuit model and studying the distributions of the electric field and surface currents of the structure. Furthermore, a specific design feature also makes our device insensitive to the incident angle and the polarization state of the impinging microwave. The 90% absorption and shielding performance of the proposed optical window avail it for a wide range of great potential applications, such as the displays of military and medical precision devices.

Strong fluorescence blinking of large-size all-inorganic perovskite nano-spheres.

We demonstrated strong fluorescence blinking on large all-inorganic perovskite (CsPbBr3) nano-spheres. By performing (time-resolved) micro-photoluminescence (µ-PL) measurements, the unique blinking characteristics of the as-grown nano-spheres with diameters of hundred nanometers, are clearly observed. Blinking has no obvious on/off states, which is different from the blinking characteristics of quantum dots. It is believed that the blinking of fluorescence is caused by metastable defect-induced trapping of carriers on the surface of the nano-spheres, because dramatically suppressed fluorescence blinking and the decay rates of ultrafast carriers are realized by surface passivation of the nano-spheres. Surface defects are closely related to the ambient atmosphere, which has been further confirmed by PL measurements of the as-grown nano-spheres in vacuum. Additionally, we also found that the fluorescence blinking was significantly suppressed as the sample size increased, which can be attributed to the large-size induced average effect on fluorescence blinking. These results may be important for understanding the mechanism of the fluorescence blinking of perovskite materials and for developing optical devices with good fluorescence stability.

Synthesis of poly(phenylacetylene)s containing chiral phenylethyl carbamate residues as coated-type CSPs with high solvent tolerability.

Two novel helical poly(phenylacetylene) derivatives containing chiral phenylethyl carbamate residues in the end of each side chain (PPA-S and PPA-R) were synthesized by polymerization of the corresponding phenylacetylene monomers using Rh(nbd)BPh4 as a catalyst in DMF. The enantioseparation properties of the polymers were evaluated as coated-type chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC). Under the same chromatographic conditions, PPA-S and PPA-R showed different enantioseparation properties, indicating that the different interactions between the analytes and the polymers, which result from the different chiral phenylethyl carbamate groups in the end of each side chains. Racemates 1, 7, and 8 could be better resolved on PPA-S, while racemate 6 was separated on PPA-R more efficiently. In addition, the coated-type CSPs showed good solvent tolerability and could work without any damage by introducing the polar solvents, such as CHCl3 and THF, in eluent. Moreover, some racemates could be better resolved on these coated-type CSPs with the addition of THF to the eluent.

Dynamics of excited-state condensate for optically confined exciton-polaritons.

We report experimental studies on the dynamics of excited-state condensate for exciton-polaritons confined in an optically generated trap. The three-dimensionally confined trap was realized by imposing two optical barriers onto a one-dimensional ZnO whispering gallery microcavity. Experimentally, we characterized the confined polariton condensate by varying the trap width and the barrier height. Theoretically, we calculated the spatial overlap between the polariton wavefunction and the excitonic reservoir. Direct comparison of these results verified that such polariton-reservoir overlap was responsible for the observed excited-state polariton condensate.

An All-Inorganic Perovskite-Phase Rubidium Lead Bromide Nanolaser.

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.

Fabry-Perot type polariton modes and their dynamics revealed by Young's interference experiment.

We report experimental studies on the Fabry-Perot (F-P) type polariton modes and their dynamics using a modified Young's double-slit interference technique. The technique was based on the angle-resolved micro-photoluminescence spectroscopy and optimized for nanostructure measurements. Using this technique, we directly revealed the parity of the F-P type polariton modes from the angle-dependent interference spectra. Moreover, clear features of mode competition were observed from the power dependence of the interference patterns. The observed competition behaviors can be well simulated by a five-level rate equation model.

Hybridization-induced broadband terahertz wave absorption with graphene metasurfaces.

Electromagnetic (EM) wave absorption plays a vital role in photonics. While metasurfaces are proposed to absorb EM waves efficiently, most of them exhibit limited bandwidth and fixed functionalities. Here, we propose a broadband and tunable terahertz (THz) absorber based on a graphene-based metasurface, which is constructed by a single layer of closely patterned graphene concentric double rings and a metallic mirror separated by an ultrathin SiO2 layer. Plasmonic hybridization between two graphene rings significantly enlarges the absorption bandwidth, which can be further tuned by gating the graphene. Moreover, the specific design also makes our device insensitive to the incident angle and polarization state of impinging EM waves. Our results may inspire certain wave-modulation-related applications, such as THz imaging, smart absorber, tunable sensor, etc.

A surface molecularly imprinted polymer as chiral stationary phase for chiral separation of 1,1'-binaphthalene-2-naphthol racemates.

Acrylamide (AM) was copolymerized with ethylene glycol dimethacrylate (EGDMA) in the presence of (R)-1,1'-binaphthalene-2-naphthol (BINOL) as the template molecules on the surface of silica gel by a free radical polymerization to produce a chiral stationary phase based on the surface molecularly imprinted polymer (SMIP-CSP). The SMIP-CSP showed a much better separation factor (α = 4.28) than the CSP based on the molecularly imprinted polymer (MIP-CSP) without coating on the silica gel (α = 1.96) during the chiral separation of BINOL enantiomers by high-performance liquid chromatography. The influence of the pretreatment temperature and the content of the template molecule ((R)-BINOL) of the SMIP-CSP, and the mobile phase composition on the separation of the racemic BINOL were systematically investigated.

Temperature-Triggered Switchable Helix-Helix Inversion of Poly(phenylacetylene) Bearing l-Valine Ethyl Ester Pendants and Its Chiral Recognition Ability.

A phenylacetylene containing the l-valine ethyl ester pendant (PAA-Val) was synthesized and polymerized by an organorhodium catalyst (Rh(nbd)BPh4) to produce the corresponding one-handed helical cis-poly(phenylacetylene) (PPAA-Val). PPAA-Val showed a unique temperature-triggered switchable helix-sense in chloroform, while it was not observed in highly polar solvents, such as N,N'-dimethylformamide (DMF). By heating the solution of PPAA-Val in chloroform, the sign of the CD absorption became reversed, but recovered after cooling the solution to room temperature. Even after six cycles of the heating-cooling treatment, the helix sense of the PPAA-Val's backbone was still switchable without loss of the CD intensity. The PPAA-Val was then coated on silica gel particles to produce novel chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC). These novel PPAA-Val based CSPs showed a high chiral recognition ability for racemic mandelonitrile (α = 2.18) and racemic trans-N,N'-diphenylcyclohexane-1,2-dicarboxamide (α = 2.60). Additionally, the one-handed helical cis-polyene backbone of PPAA-Val was irreversibly destroyed to afford PPAA-Val-H by heating in dimethyl sulfoxide (DMSO) accompanied by the complete disappearance of the Cotton effect. Although PPAA-Val-H had the same l-valine ethyl ester pendants as its cis-isomer PPAA-Val, it showed no chiral recognition. It was concluded that the one-handed helical cis-polyene backbone of PPAA-Val plays an important role in the chiral recognition ability.

Continuous-Wave Pumped Monolayer WS2 Lasing for Photonic Barcoding.

Micro/nano photonic barcoding has emerged as a promising technology for information security and anti-counterfeiting applications owing to its high security and robust tamper resistance. However, the practical application of conventional micro/nano photonic barcodes is constrained by limitations in encoding capacity and identification verification (e.g., broad emission bandwidth and the expense of pulsed lasers). Herein, we propose high-capacity photonic barcode labels by leveraging continuous-wave (CW) pumped monolayer tungsten disulfide (WS2) lasing. Large-area, high-quality monolayer WS2 films were grown via a vapor deposition method and coupled with external cavities to construct optically pumped microlasers, thus achieving an excellent CW-pumped lasing with a narrow linewidth (~0.39 nm) and a low threshold (~400 W cm-2) at room temperature. Each pixel within the photonic barcode labels consists of closely packed WS2 microlasers of varying sizes, demonstrating high-density and nonuniform multiple-mode lasing signals that facilitate barcode encoding. Notably, CW operation and narrow-linewidth lasing emission could significantly simplify detection. As proof of concept, a 20-pixel label exhibits a high encoding capacity (2.35 × 10108). This work may promote the advancement of two-dimensional materials micro/nanolasers and offer a promising platform for information encoding and security applications.