Light-Emitting Nanophotonic Designs Enabled by Ultrafast Laser Processing of Halide Perovskites

Anisotropic Vanadium Dioxide Nanogratings by Direct Laser-Induced Periodic Surface Structuring (LIPSS)

Thermochromic vanadium dioxide (VO2) films have attracted enormous attention in the past decade owing to their high potential in active optical filters, sensors, anevices. VO2 patterned at the micro- and nanoscale is an evident route toward next-generation devices justifying the need for scalable, straightforward, and high-performing nanofabrication technologies being easily applied for this material. Herein, precise and nondestructive femtosecond laser nanopatterning of the VO2 films in both direct ablation and plasmon-assisted self-organization regimes is reported under ambient conditions. Our studies unveil formation of the spatially uniform subwavelength nanogratings (or laser-induced periodic surface structures) with a periodicity of around 100 nm through optical excitation and interference of the surface plasmons in the VO2 film upon its multipulse irradiation. Plasmon-assisted nanotexturing preserves pristine composition of the film, strongly modulating its optical properties toward enhanced visible-range transmittance and evident thermochromic anisotropy in the near-IR spectral range. Overall, our study not only sheds light onto the origin of the laser-driven self-organization in the VO2 films, but also unveils huge potential of scalable nondestructive direct fs-laser patterning for creating novel optoelectronic and sensing devices based on the optically anisotropic nanotextured VO2 films.

Laser-Controlled Information Releasing and Hiding Based on Perovskite Phosphors

Laser-active interference with high confidentiality and convenience opens up a cutting-edge path for releasing and hiding key targets; however, its development still faces enormous challenges owing to the difficulty of concealing objects. Herein, a novel conceptual design for laser-controlled information release and hiding (LIRH) is proposed and successfully realized. Cs2NaInCl6:Er3+, Yb3+ (CNIC:Er, Yb) perovskite microcrystal is adopted as a carrier for LIRH implementation, exhibiting excellent up-conversion (UC) emission under NIR (980 and 1530 nm) irradiation due to its ultralow phonon energy. The fluorescence intensity crossover and outstanding photon output capacity are revealed in comparison with Er3+/Yb3+ codoped and Er3+ single-doped CNIC phosphors under different laser sources, and the obvious difference in quantum yields (QY) under 980 and 1530 nm excitation provides theoretical possibility for LIRH. More importantly, the obtained LIRH features high stability at temperatures up to 413 K, showing good adaptability in various potential scenarios. Moreover, CNIC:Er, Yb is further combined with polyacrylonitrile (PAN) polymer to form fluorescent fibers with exceptional crystal stability and composite flexibility, thus making the LIRH code a reality based on perovskite composite phosphors. The laser-active invisibility offers an innovative idea for LIRH, further extending the application of LIRH in the field of information encryption, which has promising prospects in information safety, advanced anticounterfeiting, and smart responsive materials.

Photoinduced Transition from Quasi-Two-Dimensional Ruddlesden-Popper to Three-Dimensional Halide Perovskites for the Optical Writing of Multicolor and Light-Erasable Images

Optical data storage, information encryption, and security labeling technologies require materials that exhibit local, pronounced, and diverse modifications of their structure-dependent optical properties under external excitation. Herein, we propose and develop a novel platform relying on lead halide Ruddlesden-Popper phases that undergo a light-induced transition toward bulk perovskite and employ this phenomenon for the direct optical writing of multicolor patterns. This transition causes the weakening of quantum confinement and hence a reduction in the band gap. To extend the color gamut of photoluminescence, we use mixed-halide compositions that exhibit photoinduced halide segregation. The emission of the films can be tuned across the range of 450-600 nm. Laser irradiation provides high-resolution direct writing, whereas continuous-wave ultraviolet exposure is suitable for recording on larger scales. The luminescent images created on such films can be erased during the visualization process. This makes the proposed writing/erasing platform suitable for the manufacturing of optical data storage devices and light-erasable security labels.

Photoluminescent Microbit Inscripion Inside Dielectric Crystals by Ultrashort Laser Pulses for Archival Applications

Inscription of embedded photoluminescent microbits inside micromechanically positioned bulk natural diamond, LiF and CaF₂ crystals was performed in sub-filamentation (geometrical focusing) regime by 525 nm 0.2 ps laser pulses focused by 0.65 NA micro-objective as a function of pulse energy, exposure and inter-layer separation. The resulting microbits were visualized by 3D-scanning confocal Raman/photoluminescence microscopy as conglomerates of photo-induced quasi-molecular color centers and tested regarding their spatial resolution and thermal stability via high-temperature annealing. Minimal lateral and longitudinal microbit separations, enabling their robust optical read-out through micromechanical positioning, were measured in the most promising crystalline material, LiF, as 1.5 and 13 microns, respectively, to be improved regarding information storage capacity by more elaborate focusing systems. These findings pave a way to novel optomechanical memory storage platforms, utilizing ultrashort-pulse laser inscription of photoluminescent microbits as carriers of archival memory.

High-Resolution Patterning of Perovskite Quantum Dots via Femtosecond Laser-Induced Forward Transfer

High-resolution patterning of perovskite quantum dots (PQDs) is of significant importance for satisfying various practical applications, including high-resolution displays and image sensing. However, due to the limitation of the instability of PQDs, the existing patterning strategy always involves chemical reagent treatment or mask contact that is not suitable for PQDs. Therefore, it is still a challenge to fabricate high-resolution full-color PQD arrays. Here, we present a femtosecond laser-induced forward transfer (FsLIFT) technology, which enables the programmable fabrication of high-resolution full-color PQD arrays and arbitrary micropatterns. The FsLIFT process integrates transfer, deposition, patterning, and alignment in one step without involving a mask and chemical reagent treatment, guaranteeing the preservation of the photophysical properties of PQDs. A full-color PQD array with a high resolution of 2 μm has been successfully achieved. We anticipate that our facile and flexible FsLIFT technology can facilitate the development of diverse practical applications based on patterned PQDs.

Ultrafast materials synthesis and manufacturing techniques for emerging energy and environmental applications

Energy and environmental issues have attracted increasing attention globally, where sustainability and low-carbon emissions are seriously considered and widely accepted by government officials. In response to this situation, the development of renewable energy and environmental technologies is urgently needed to complement the usage of traditional fossil fuels. While a big part of advancement in these technologies relies on materials innovations, new materials discovery is limited by sluggish conventional materials synthesis methods, greatly hindering the advancement of related technologies. To address this issue, this review introduces and comprehensively summarizes emerging ultrafast materials synthesis methods that could synthesize materials in times as short as nanoseconds, significantly improving research efficiency. We discuss the unique advantages of these methods, followed by how they benefit individual applications for renewable energy and the environment. We also highlight the scalability of ultrafast manufacturing towards their potential industrial utilization. Finally, we provide our perspectives on challenges and opportunities for the future development of ultrafast synthesis and manufacturing technologies. We anticipate that fertile opportunities exist not only for energy and the environment but also for many other applications.

Security labeling and optical information encryption enabled by laser-printed silicon Mie resonators

Fighting against the falsification of valuable items remains a crucial social-threatening challenge stimulating a never-ending search for novel anti-counterfeiting strategies. The demanding security labels must simultaneously address multiple requirements (high density of the recorded information, high protection degree, etc.) and be realized via scalable and inexpensive technologies. Here, the direct reproducible femtosecond-laser patterning of thin glass-supported amorphous (α-)Si films is proposed for optical information encryption and the scalable and highly reproducible fabrication of security labels composed of Raman-active hemispherical Si nanoparticles (NPs). Laser printing conditions allow the precise control of the diameter of the formed NPs ensuring translation of their dipolar Mie resonance position within the entire visible spectral range. Two-temperature molecular dynamics simulations clarify the origin of α-Si NP formation by rupture of the molten Si layer driven by a negative GPa-range pressure near the liquid-solid interface. Arrangement of the laser-printed Mie-resonant NP allows the creation of hidden security labels offering several easy-to-realize information encryption strategies (for example, local laser-induced post-crystallization or mixing Mie-resonant and non-resonant NPs), additional protection modalities, facile Raman mapping readout and dense information recording (up to 60 000 dots per inch) close to the optical diffraction limit. The developed fabrication strategy is simple, inexpensive, and scalable and can be realized based on cheap Earth-abundant materials and commercially-available equipment justifying its practical applicability and attractiveness for anti-counterfeit and security applications.

Nanopatterning of Perovskite Thin Films for Enhanced and Directional Light Emission

Lead-halide perovskites offer excellent properties for lighting and display applications. Nanopatterning perovskite films could enable perovskite-based devices with designer properties, increasing their performance and adding novel functionalities. We demonstrate the potential of nanopatterning for achieving light emission of a perovskite film into a specific angular range by introducing periodic sol-gel structures between the injection and emissive layer by using substrate conformal imprint lithography (SCIL). Structural and optical characterization reveals that the emission is funnelled into a well-defined angular range by optical resonances, while the emission wavelength and the structural properties of the perovskite film are preserved. The results demonstrate a flexible and scalable approach to the patterning of perovskite layers, paving the way toward perovskite LEDs with designer angular emission patterns.

Multifunctional and Transformative Metaphotonics with Emerging Materials

Future technologies underpinning multifunctional physical and chemical systems and compact biological sensors will rely on densely packed transformative and tunable circuitry employing nanophotonics. For many years, plasmonics was considered as the only available platform for subwavelength optics, but the recently emerged field of resonant metaphotonics may provide a versatile practical platform for nanoscale science by employing resonances in high-index dielectric nanoparticles and metasurfaces. Here, we discuss the recently emerged field of metaphotonics and describe its connection to material science and chemistry. For tunabilty, metaphotonics employs a variety of the recently highlighted materials such as polymers, perovskites, transition metal dichalcogenides, and phase change materials. This allows to achieve diverse functionalities of metasystems and metasurfaces for efficient spatial and temporal control of light by employing multipolar resonances and the physics of bound states in the continuum. We anticipate expanding applications of these concepts in nanolasers, tunable metadevices, metachemistry, as well as a design of a new generation of chemical and biological ultracompact sensing devices.

Direct Laser Writing of Copper Micropatterns from Deep Eutectic Solvents Using Pulsed near-IR Radiation

In this study, we developed a method for the fabrication of electrically conductive copper patterns of arbitrary topology and films on dielectric substrates, by improved laser-induced synthesis from deep eutectic solvents. A significant increase in the processing efficiency was achieved by acceptor substrate pretreatment, with the laser-induced microplasma technique, using auxiliary glass substrates and optional laser post-processing of the recorded structures; thus, the proposed approach offers a complete manufacturing cycle, utilizing a single, commercially available, pulsed Yb fiber laser system. The potential implications of the presented research are amplified by the observation of laser-induced periodic surface structures (LIPSSs) that may be useful for the further tuning of tracks' functional properties.

Perovskite metasurfaces with large superstructural chirality

Recent attempts to synthesize hybrid perovskites with large chirality have been hampered by large size mismatch and weak interaction between their structure and the wavelength of light. Here we adopt a planar nanostructure design to overcome these limitations and realize all-dielectric perovskite metasurfaces with giant superstructural chirality. We identify a direct spectral correspondence between the near- and the far- field chirality, and tune the electric and magnetic multipole moments of the resonant chiral metamolecules to obtain large anisotropy factor of 0.49 and circular dichroism of 6350 mdeg. Simulations show that larger area metasurfaces could yield even higher optical activity, approaching the theoretical limits. Our results clearly demonstrate the advantages of nanostructrure engineering for the implementation of perovskite chiral photonic, optoelectronic, and spintronic devices.

Though chiral hybrid organic-inorganic perovskites are attractive for next-generation optoelectronics, imparting strong chirality through chemical synthesis has proved challenging. Here, the authors report all-dielectric perovskite metasurfaces with giant superstructural chirality via planar nanostructuring.

Directional Lasing from Nanopatterned Halide Perovskite Nanowire

Halide perovskite nanowire-based lasers have become a powerful tool for modern nanophotonics, being deeply subwavelength in cross-section and demonstrating low-threshold lasing within the whole visible spectral range owing to the huge gain of material even at room temperature. However, their emission directivity remains poorly controlled because of the efficient outcoupling of radiation through their subwavelength facets working as pointlike light sources. Here, we achieve directional lasing from a single perovskite CsPbBr₃ nanowire by imprinting a nanograting on its surface, which provides stimulated emission outcoupling to its vertical direction with a divergence angle around 2°. The nanopatterning is carried out by the high-throughput laser ablation method, which preserves the luminescent properties of the material that is typically deteriorated after processing via conventional lithographic approaches. Moreover, nanopatterning of the perovskite nanowire is found to decrease the number of the lasing modes with a 2-fold increase of the quality factor of the remaining modes.

Lithographic in-mold patterning for CsPbBr3 nanocrystals distributed Bragg reflector single-mode laser

Extensive studies on lead halide perovskites have shown that these materials are excellent candidates as gain mediums. Recently, many efforts have been made to incorporate perovskite lasers in integrated optical circuits. Possible solutions would be to utilize standard lithography with an etching/lift-off process or a direct laser etching technique. However, due to the fragile nature of the lead halide perovskites which gives rise to significant material deterioration during the lithography and etching processes, realizing a small-size, low-roughness, and single-mode laser remains a challenge. Here, a lithographic in-mold patterning method realized by nanocrystal concentration control and a multi-step filling-drying process is proposed to demonstrate CsPbBr₃ nanocrystals distributed-Bragg-reflector (DBR) waveguide lasers. This method realizes the patterning of the CsPbBr₃ nanocrystal laser cavity and DBR grating without lift-off and etching processes, and the smallest fabricated structures are obtained in a few hundred nanometers. The single-mode lasing is demonstrated at room temperature with a threshold of 23.5 μJ cm^-2. The smallest full width at half maximum FWHM of the laser output is 0.4 nm. Due to the fabrication process and the DBR laser geometry, the lasers can be fabricated in a compact array, which is important for incorporating perovskite-based lasers in complex optoelectronic circuits.

Recent Progress on Patterning Strategies for Perovskite Light-Emitting Diodes toward a Full-Color Display Prototype

Perovskite light-emitting diodes (PeLEDs) have attracted both academic and industrial interest because of their high efficiency, wide color gamut as well as low material and fabrication costs. However, most state-of-the-art PeLEDs are still fabricated with commonly used spin-coating methods, which are undesirable for large-scale commercial production. Achieving highly emissive perovskite microarrays at high spatial resolution with quick and large-scale growth is one of the critical steps to integrate state-of-the-art PeLEDs into full-color display panels. Here, the fabrication methods and crystallization processes of perovskite materials are first discussed because they are strongly relevant to the patterning process and the quality of the perovskite pixels. Then, the current strategies to realize perovskite patterns that can be likely integrated into display panels, through mask-free or mask-assisted methods, are explored. Self-emitting and down-conversion PeLED devices with a patterned perovskite matrix as the emissive layer are also reviewed. Finally, an outlook is provided on how to further improve the optical and electrical properties of the perovskite patterns and the performance of PeLEDs as well as to develop eco-friendly devices to accelerate the potential commercialization progress of this young technique.

Whispering Gallery Mode Lasing from Perovskite Polygonal Microcavities via Femtosecond Laser Direct Writing

Organic-inorganic halide perovskites have excellent intrinsic properties, such as long carrier lifetime, high photoluminescence quantum yield, and high gain, in whispering gallery mode (WGM) cavities by facile vapor self-assembly or solution process, which make them competitive for high-performance microlasers. However, the performance of perovskite-based microlasers is severely limited by the fabrication of microcavities, which results in poor reproducibility and uncontrolled morphology. Herein, we explore a reproducible method which combined thermal co-evaporation with femtosecond (fs) laser direct writing for formamidinium lead iodide (FAPbI₃) perovskite polygon-shaped WGM microcavities. The microlasers pumped with the fs laser had a low threshold of 4.0-12.3 μJ/cm² and narrow full width at half-maximum of 0.62-1.05 nm. Moreover, size- and shape-dependent WGM lasing performances are also investigated systematically. The results prove that FAPbI₃ polygonal microcavities can serve as promising WGM lasers and have great potential for practical optoelectronic applications.

High optical enhancement in Au/Ag alloys and porous Au using Surface-Enhanced Raman spectroscopy technique

We report high optical enhancement in Ag/Au alloys and porous gold nanostructures using Surface Enhanced Raman Spectroscopy (SERS) technique. Scanning electron microscopy investigation shows the formation of Ag/Au alloys particles during irradiation of Ag-Au bilayer deposited on FTO (SnO2:F) substrate by laser fluency equal to 0.5 J/cm2 or 1.0 J/cm2 with 12 ns laser pulse duration. The dealloying process of these Au-Ag alloy particles leads to the formation of Au nanoporous particles. The obtained nanostructures were studied with SERS and revealed a promising enhancement factor in porous Au nanostructure and tunability of localized surface plasmon resonance. The highly dense strong hot spots and large specific area in porous structure of gold nanostructures is the origin of the highly enhancement factor observed experimentally and theoretically. A very good agreement between simulation and experimental results was found confirming the potential of Au/Ag alloys and particularly porous gold nanostructure in SERS application.

Large-Scale and Localized Laser Crystallization of Optically Thick Amorphous Silicon Films by Near-IR Femtosecond Pulses

Amorphous silicon (α-Si) film present an inexpensive and promising material for optoelectronic and nanophotonic applications. Its basic optical and optoelectronic properties are known to be improved via phase transition from amorphous to polycrystalline phase. Infrared femtosecond laser radiation can be considered to be a promising nondestructive and facile way to drive uniform in-depth and lateral crystallization of α-Si films that are typically opaque in UV-visible spectral range. However, so far only a few studies reported on use of near-IR radiation for laser-induced crystallization of α-Si providing less information regarding optical properties of the resultant polycrystalline Si films demonstrating rather high surface roughness. The present work demonstrates efficient and gentle single-pass crystallization of α-Si films induced by their direct irradiation with near-IR femtosecond laser pulses coming at sub-MHz repetition rate. Comprehensive analysis of morphology and composition of laser-annealed films by atomic-force microscopy, optical, micro-Raman and energy-dispersive X-ray spectroscopy, as well as numerical modeling of optical spectra, confirmed efficient crystallization of α-Si and high-quality of the obtained films. Moreover, we highlight localized laser-induced crystallization of α-Si as a promising way for optical information encryption, anti-counterfeiting and fabrication of micro-optical elements.

Improved light extraction in all-inorganic perovskite light-emitting devices with periodic nanostructures by nanoimprinting lithography

We report an improved light extraction in all-inorganic perovskite light-emitting devices (PeLEDs) by integrating a periodic corrugated nanostructure at the metallic cathode/organic interface. Nanoimprinting lithography was used to introduce the nanostructures onto the surface of the electron transport layer directly to avoid influencing the morphology and crystallinity of the perovskite film underneath. The trapped energy at the metallic electrode has been successfully outcoupled by the excitation of the surface plasma polariton (SPP) modes induced by the periodic corrugations. The luminance and current efficiency of the periodically corrugated PeLED exhibit enhancements of 42% and 28%, respectively, compared to those of the planar PeLED. The finite-difference time-domain simulation was used to confirm the efficient outcoupling of the SPP modes.