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.

Fluorescent incandescent light sources from individual quadrilateral ZnO microwire via Ga-incorporation.

By means of nanophotonics principle, the thermal radiation can be tailored, thus, traditional tungsten lamp light source can glow the vitality and the vigor due to the low-efficiency approaching to commercial fluorescent or light-emitting diode bulbs. However, too far by demanding exacting terms, such as high-temperature thermal radiation (∼ 3000 K), high-vacuum encapsulation technology, restricted spectrally controllable source and so on, tungsten-based incandescent lamp filament has greatly limited the application in lighting, diagnosis and treatment, communication, imaging, etc. Herein, individual Ga-doped ZnO microwires (ZnO:Ga MWs) were successfully synthesized, which can be utilized to construct typical incandescent sources. By adjusting the Ga-incorporation, lighting colors are tuned in the visible spectral band. Especially, by incorporating Au quasiparticle nanofilms, the incandescent lighting features can further be modulated, such as the emission peaks, the modulation of lighting regions. Therefore, individual ZnO:Ga MWs based incandescent emitters can undertake a new function of the oldest, affordable and easily prepared light sources. While preliminary, individual ZnO:Ga MWs being treated as efficient incandescent light sources, can also open up intriguing scientific questions, and possible applications of linear, transparent, flexible displays and optical interconnects with electronic circuits.

Wavelength-Tunable Waveguide Emissions from Electrically Driven Single ZnO/ZnO:Ga Superlattice Microwires.

Because of the superlattice structures comprising periodic and alternating crystalline layers, one-dimensional photon crystals can be employed to expand immense versatility and practicality of modulating the electronic and photonic propagation behaviors, as well as optical properties. In this work, individual superlattice microwires (MWs) comprising ZnO and Ga-doped ZnO (ZnO/ZnO:Ga) layers were successfully synthesized. Wavelength-tunable multipeak emissions can be realized from electrically driven single superlattice MW-based emission devices, with the dominant wavelengths tuned from ultraviolet to visible spectral regions. To illustrate the multipeak character, single superlattice MWs were selected to construct fluorescent emitters, and the emission wavelength could be tuned from 518 to 562 nm, which is dominated by Ga incorporation. Especially, by introducing Au quasiparticle film decoration, emission characteristics can further be modulated, such as the red shift of the emission wavelengths, and the multipeaks were strongly modified and split into more and narrower subbands. In particular, electrically pumped exciton-polariton emission was realized from heterojunction diodes composed of single ZnO/ZnO:Ga superlattice MWs and p-GaN layers in the blue-ultraviolet spectral regions. With the aid of localized surface plasmons from Au nanoparticles, which deposited on the superlattice MW, significant improvement of emission characteristics, such as enhancement of output efficiencies, blue shift of the dominant emission wavelengths, and narrowing of the spectral linewidth, can be achieved. The multipeak emission characteristics would be originated from the typical optical cavity modes, but not the Fabry-Perot mode optical cavity formed by the bilateral sides of the wire. The resonant modes are likely attributed to the coupled optical microcavities, which formed along the axial direction of the wire; thus, the emitted photons can be propagated and selected longitudinally. Therefore, the novel ZnO/ZnO:Ga superlattice MWs with a quadrilateral cross section can provide a potential platform to construct multicolor emitters and low-threshold exciton-polariton diodes and lasers.