Fabrication of Super-Sized Metal Inorganic-Organic Hybrid Glass with Supramolecular Network via Crystallization-Suppressing Approach.

Metal coordination compound (MCC) glasses [e.g., metal-organic framework (MOF) glass, coordination polymer glass, and metal inorganic-organic complex (MIOC) glass] are emerging members of the hybrid glass family. So far, a limited number of crystalline MCCs can be converted into glasses by melt-quenching. Here, we report a universal wet-chemistry method, by which the super-sized supramolecular MIOC glasses can be synthesized from non-meltable MOFs. Alcohol and acid were used as agents to inhibit crystallization. The MIOC glasses demonstrate unique features including high transparency, shaping capability, and anisotropic network. Directional photoluminescence with a large polarization ratio (≈47 %) was observed from samples doped with organic dyes. This crystallization-suppressing approach enables fabrication of super-sized MCC glasses, which cannot be achieved by conventional vitrification methods, and thus allows for exploring new MCC glasses possessing photonic functionalities.

Effectively writing low propagation and bend loss waveguides in the silica glass by using a femtosecond laser.

We report writing low-loss waveguides (WGs) by using a femtosecond laser in silica glass. A record low propagation loss of 0.07 dB/cm is achieved, and the lowest bend loss reaches 0.001 dB/mm with the bend radius of 30 mm. The optimal effective writing speed reaches 125 µm/s, which is two orders higher than the previous reported value. Fan-out devices with well controllable low loss for three-dimensional photonic integration are also fabricated. This work provides an effective strategy to create WG devices for 3D high-density photonic integration.

Long-term optical information storage in glass with ultraviolet-light-preprocessing-induced enhancement of the signal-to-noise ratio.

This Letter describes the realization of long-term optical information storage in glass using an enhanced signal-to-noise ratio (SNR). We show that the photo-oxidation of Eu2+ ions in the glass matrix induced by ultraviolet light suppresses background signals, thereby enhancing by tenfold the SNR of Eu2+ ions photoluminescence (PL) of the dots written by a femtosecond (fs) laser. Thus, smaller dots exhibiting weak PL emission can be detected. In addition, the stored information shows excellent stability under the light irradiation with the power density up to 240W/cm2. Accelerated-aging experiments indicate that the stored data can retain stability for more than 115 years at room temperature. The optical storage capacity is approximately 270Gbitcm-3. This technique enables long-term, high-capacity data storage in glass media.

Single-shot photon recording for three-dimensional memory with prospects of high capacity.

Femtosecond laser-induced modification in the glass has drawn considerable interest due to its widespread superiority in the applications of three-dimensional optical storage. In this Letter, we report that a single pulse could be used in optical memory with super-high writing speed. The photoluminescence image and spectrum indicate that one pulse-induced permanent photoreduction of Sm3+ to Sm2+ in Sm3+-doped sodium aluminoborate glass can be achieved. Consequently, strong emission contrast is obtained, which is used for optical storage. By regulating the fabrication conditions, the fluorescent diameter could be controlled to approximately 800 nm, which demonstrates the feasibility in super-high density optical storage. Besides, multi-layer information is successfully inscribed. The proposed technique of single-pulse writing holds great potential for optical memory with high speed and huge capacity.

Fabricating low loss waveguides over a large depth in glass by temperature gradient assisted femtosecond laser writing.

We propose a strategy of temperature gradient assisted femtosecond laser writing for elaboration of low loss waveguides (WGs) over a large depth in glass. The matter flow driven by the temperature distribution is responsible for forming a highly densified WG core with tunable size. Importantly, the unique position of the guiding core outside the focus allows for abating the influence of laser energy redistribution and inscribing low loss deep WGs. A low insertion loss (Li) of 0.6 dB at 1550 nm is achieved for WGs at the depth from 300 µm to 900 µm. Establishing strong dependence of Li on the WG size offers a unique route to improve WG performance. These findings highlight that the present method would provide new opportunities for creating low loss WG lattices at large depth.

Carrier Transport and Photoresponse in GeSe/MoS2 Heterojunction p-n Diodes.

Simple stacking of thin van der Waals 2D materials with different physical properties enables one to create heterojunctions (HJs) with novel functionalities and new potential applications. Here, a 2D material p-n HJ of GeSe/MoS2 is fabricated and its vertical and horizontal carrier transport and photoresponse properties are studied. Substantial rectification with a very high contrast (>104 ) through the potential barrier in the vertical-direction tunneling of HJs is observed. The negative differential transconductance with high peak-to-valley ratio (>105 ) due to the series resistance change of GeSe, MoS2 , and HJs at different gate voltages is observed. Moreover, strong and broad-band photoresponse via the photoconductive effect are also demonstrated. The explored multifunctional properties of the GeSe/MoS2 HJs are expected to be important for understanding the carrier transport and photoresponse of 2D-material HJs for achieving their use in various new applications in the electronics and optoelectronics fields.

Enhanced broadband excited upconversion luminescence in Ho-doped glasses by codoping with bismuth.

We report enhanced green and red upconversion (UC) luminescence in Ho3+-doped oxyfluoride germanate glass by introducing bismuth near-infrared active centers as sensitizers. The UC excitation bands at 750 and 970 nm show a full width at half-maximum of 20 and 45 nm, respectively. Energy transfer from sensitizers, the excited-state absorption, and phonon-coupled absorption of Ho3+ jointly contribute to the enhanced UC luminescence. Our approach provides an efficient methodology to broaden the excitation bandwidth of UC luminescent materials, which may have the potential for promising application in solar cells.

Precise mode control of laser-written waveguides for broadband, low-dispersion 3D integrated optics.

Three-dimensional (3D) glass chips are promising waveguide platforms for building hybrid 3D photonic circuits due to their 3D topological capabilities, large transparent windows, and low coupling dispersion. At present, the key challenge in scaling down a benchtop optical system to a glass chip is the lack of precise methods for controlling the mode field and optical coupling of 3D waveguide circuits. Here, we propose an overlap-controlled multi-scan (OCMS) method based on laser-direct lithography that allows customizing the refractive index profile of 3D waveguides with high spatial precision in a variety of glasses. On the basis of this method, we achieve variable mode-field distribution, robust and broadband coupling, and thereby demonstrate dispersionless LP21-mode conversion of supercontinuum pulses with the largest deviation of <0.1 dB in coupling ratios on 210 nm broadband. This approach provides a route to achieve ultra-broadband and low-dispersion coupling in 3D photonic circuits, with overwhelming advantages over conventional planar waveguide-optic platforms for on-chip transmission and manipulation of ultrashort laser pulses and broadband supercontinuum.

Localized Temperature Engineering Enables Writing of Heterostructures in Glass for Polarized Photoluminescence of Perovskites.

Metal halide perovskite (MHP) structures that exhibit polarized photoluminescence (PL) have attracted significant interest in fabricating light field regulation elements for display, imaging, and information storage applications. We report a three-dimensional direct lithography of heterostructures for controllable polarized PL inside glass by laser-induced localized temperature engineering. The heterostructures consisted of oriented periodic structures (OPSs) and MHP nanocrystals, and the mechanism for hierarchical distribution of heterostructures was illustrated. The patterning of heterostructures for manipulable polarized PL can be used for information encryption, wave-plate, and polarized micro-LEDs.

Regulation of structure rigidity for improvement of the thermal stability of near-infrared luminescence in Bi-doped borate glasses.

The effect of heat-treatment on the near-infrared (NIR) luminescence properties was studied in Bi-doped borate glasses. The luminescence intensity generally decreases with the increase of temperature, and the thermal stability can be improved by nearly 4.5 times with addition of 5 mol% La2O3. Collaborative studies by using steady photoluminescence (PL) and photoluminescence excitation (PLE) spectra, luminescence decay curve, differential thermal analysis (DTA), Raman spectra and X-ray diffraction (XRD) indicate that the luminescence decrement is associated with the agglomeration of Bi active centers during heat-treatment. The improvement of the thermal stability of NIR luminescence with the addition of La2O3 is benefited from the enhancement of structure rigidity due to the strong cationic field strength of La3+. The results not only provide valuable guidance for suppressing performance degradation of Bi-doped glass during fiber drawing process, but also present an effective way to control the luminescence properties of main group elements in glasses from the perspective of glass structure.

Fabrication of silica nano/micro-fibers doped with one-dimensional assembly of silver nanoparticles.

Nano/micro fibers doped with metal nanocrystals are of great interest both theorectically and practically. Nevertheless, the ordered assembly of metal nanocrystals with desired patterns in nano/micro fibers still remains a big challenge, which constrains the further development of the performance of the material. In this investigation, we propose a facile strategy based on the sol-gel and coaxial electrospinning technique to fabricate silica submicron fibers incorporating ordered 1D array of silver nanoparticles. The silver nanoparticles align strictly in a head-to-tail manner in silica fibers, and their size, shape and population are conveniently controlled through tailoring the properties of the precursor solutions and the electrospinning parameters. Therefore, the plasmon property of the obtained fibers is tuned with great freedom. The fabrication method applied here holds great potential for low-cost preparation of metal/glass composite fibers for nano/micro optical applications in general.

3D Imprinting of Voxel-Level Structural Colors in Lithium Niobate Crystal.

Advanced coloration methods are of pivotal importance in science, technology, and engineering. However, 3D structural colors that are critical for emerging multidimensional information representation and recording are rarely achievable. Here, a facile voxel-level programmable 3D structural coloration in the bulk lithium niobate (LiNbO3 ) crystal is reported. This is achieved by engineering wavelength-selective interference between ordinary (O) and extraordinary (E) light in the crystal matrix. To induce effective phase contrast between O and E light for establishing the highly localized interference across the visible band, the presence of a pulse-internal-coupling effect is revealed in the single-pulse ultrafast laser-crystal interaction and an ultrafast-laser-induced micro-amorphization (MA) strategy is thus developed to manipulate local matrix structure. Consequently, micro-nanoscale colorful voxels can be fast inscribed into any spatial position of the crystal matrix in one step. It is demonstrated that the colors can be flexibly manipulated and quickly extracted in 3D space. Multidimensional MA-color data storage with large capacity, high writing and readout speed, long lifetime, and excellent stability under harsh conditions is achieved. The present principle enables multifunctional 3D structural coloration devices inside high-refractive-index transparent dielectrics and can serve as a general platform to innovate next-generation information optics.

Electronic State Engineering in Perovskite-Cerium-Composite Nanocrystals toward Enhanced Triplet Annihilation Upconversion.

Wavelength conversion based on hybrid inorganic-organic sensitized triplet-triplet annihilation upconversion (TTA-UC) is promising for applications such as photovoltaics, light-emitting-diodes, photocatalysis, additive manufacturing, and bioimaging. The efficiency of TTA-UC depends on the population of triplet excitons involved in triplet energy transfer (TET), the driving force in TET, and the coupling strength between the donor and acceptor. Consequently, achieving highly efficient TTA-UC necessitates the precise control of the electronic states of inorganic donors. However, conventional covalently bonded nanocrystals (NCs) face significant challenges in this regard. Herein, a novel strategy to exert control over electronic states is proposed, thereby enhancing TET and TTA-UC by incorporating ionic-bonded CsPbBr3 and lanthanide Ce3+ ions into composite NCs. These composite-NCs exhibit high photoluminescence quantum yield, extended single-exciton lifetime, quantum confinement, and uplifted energy levels. This engineering strategy of electronic states engendered a comprehensive impact, augmenting the population of triplet excitons participating in the TET process, enhancing coupling strength and the driving force, ultimately leading to an unconventional, dopant concentration-dependent nonlinear enhancement of UC efficiency. This work not only advances fundamental understanding of hybrid TTA-UC but also opens a door for the creation of other ionic-bonded composite NCs with tunable functionalities, promising innovations for next-generation optoelectronic applications.

Enhanced broadband near-infrared luminescence of Bi-doped oxyfluoride glasses.

Broadband near-infrared luminescence covering 900 to 1600 nm has been observed in Bi-doped oxyfluoride silicate glasses. The partial substitution of fluoride for oxide in Bi-doped silicate glasses leads to an increase of the intensity and lifetime of the near-infrared luminescence and blue-shift of the near-infrared emission peaks. Both Bi-doped silicate and oxyfluoride silicate glasses show visible luminescence with blue, green, orange and red emission bands when excited by ultra-violet light. Careful investigation on the luminescence properties indicates that the change of near-infrared luminescence is related to optical basicity, phonon energy of the glass matrix and crystal field around Bi active centers. These results offer a valuable way to control the luminescence properties of Bi-doped materials and may find some applications in fiber amplifier and fiber laser.

Porous YAG:Nd3+ fibers with excitation and emission in the human "NIR optical window" as luminescent drug carriers.

The design and preparation of luminescent drug carriers has been a prosperous area of research for many years. However, the excitation and/or emission wavelength of such luminescent drug carriers haven't been optimized in the so-called human "near infrared (NIR) optical window", thus restricting their practical applications. Herein, we report the synthesis of electrospun porous YAG:Nd(3+) (neodymium-doped yttrium aluminum garnet) fibers with both excitation and emission in the "NIR optical window" as luminescent drug carriers. The YAG:Nd(3+) porous fibers were characterized by SEM, TEM, XRD, scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDX), and photoluminescence (PL). Ibuprofen (IBU) was used as a model drug to evaluate the drug-loading capacities and release profiles of the samples. BMSCs (bone mesenchymal stem cells) were used as model human cells to investigate cytotoxicity. Our results indicated that the YAG:Nd(3+) fibers possessed a fine, irregularly porous fibrous morphology with an average diameter of 378 nm. The florescence of the sample (1064 nm) could be excited over a wide wavelength range in the NIR region. During the release process of IBU in simulated body fluid (SBF), along with the dissolving of the drug, the solvent entered into the pores, and the emission intensity of the YAG:Nd(3+) fibers at 1064 nm decreased gradually, owing to a quenching effect of the hydroxy groups, thus provided an approach to track and monitor drug release. In addition, cytotoxicity investigations revealed that these YAG:Nd(3+) fibers were biocompatible with human cells. Consequently, the porous YAG:Nd(3+) fibers are a promising material for applications as advanced drug carriers.

Three-dimensional direct lithography of stable perovskite nanocrystals in glass.

Material composition engineering and device fabrication of perovskite nanocrystals (PNCs) in solution can introduce organic contamination and entail several synthetic, processing, and stabilization steps. We report three-dimensional (3D) direct lithography of PNCs with tunable composition and bandgap in glass. The halide ion distribution was controlled at the nanoscale with ultrafast laser-induced liquid nanophase separation. The PNCs exhibit notable stability against ultraviolet irradiation, organic solution, and high temperatures (up to 250°C). Printed 3D structures in glass were used for optical storage, micro-light emitting diodes, and holographic displays. The proposed mechanisms of both PNC formation and composition tunability were verified.

Unusual luminescence quenching and reviving behavior of Bi-doped germanate glasses.

Here for the first time, we report an unusual annealing temperature dependent near-infrared (NIR) luminescence quenching and reviving behavior in Bi-doped MgO-Al2O3-GeO2 glasses. Systematic characterizations of the samples by using differential thermal analysis (DTA), photoluminescence and absorption spectra, X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that this phenomenon is associated with the reversible reaction of Bi⁺ and Bi° initiated by the change of local glass structure. Excitingly, wavelength tunable luminescence is also observed and it can be ascribed to selective excitation of active Bi⁺ center in different sites. These results not only open a new way for controlling luminescence properties of main group elements in glass but also provide great value for improving practical active-fiber drawing process.

Large-scale preparation of strawberry-like, AgNP-doped SiO2 microspheres using the electrospraying method.

In this paper, we report on a novel strategy for the preparation of silver nanoparticle-doped SiO(2) microspheres (Ag-SMSs) with an interesting strawberry-like morphology using a simple and efficient electrospraying method. SEM (scanning electron microscopy), TEM (transmission electron microscopy), XRD (x-ray diffraction), EDS (energy-dispersive spectroscopy) and UV-vis spectra (ultraviolet-visible spectra) were applied to investigate the morphology, structure, composition and optical properties of the hybrid microspheres, and E. coli (Escherichia coli) was used as a model microbe to evaluate their antibacterial ability. The results showed that the Ag-SMSs were environmentally stable and washing resistant. The Ag-SMSs exhibited effective inhibition against proliferation of E. coli, and their antibacterial ability could be well preserved for a long time. The environmental stability, washing resistance, efficient antibacterial ability and simple but productive preparation method endowed the Ag-SMSs with great potential for practical biomedical applications.

Surface passivated silicon nanocrystals with stable luminescence synthesized by femtosecond laser ablation in solution.

We report the synthesis of silicon nanocrystals via a one-step route, namely, femtosecond laser ablation in 1-hexene under ambient conditions. The size of these silicon nanocrystals is 2.37 ± 0.56 nm as determined by transmission electron microscopy. Fourier transform infrared spectra and X-ray photoelectron spectra indicate that the surface of the silicon nanocrystals is passivated by organic molecules and is also partially oxidized by O(2) and H(2)O dissolved in the solution. These silicon nanocrystals emit stable and bright blue photoluminescence. We suggest that the photoluminescence originates from the radiative recombination of electron-hole pairs through the oxide-related centers on the surface of the silicon nanocrystals. The decay rate of the oxide-related surface recombination can be comparable to that of the direct band gap transition. In the excitation and emission spectra, a vibrational structure with nearly constant spacings (0.18 eV) is observed. We propose that the strong electron-phonon coupling between excitons and the longitudinal optical (LO) phonons of the Si-C vibration is responsible for this vibrational structure. The fluctuations in the peak resolution, about ±0.01 eV, are ascribed to the size distribution and presence of Si-O vibrations. These silicon nanocrystals offer stable luminescence and are synthesized through a "green" and simple route. They may find important applications in many fields, such as bioimaging and environmental science.

[The effects of hinge structure on the biological activity of antimicrobial peptides and its application in molecular design: a review].

The hinge structure, also known as hinge region or bend, is a special structure found in some antimicrobial peptides. Most studies on antimicrobial peptides focused on the standard secondary structure of α-helix and ß-sheet, while the hinge structure and its functions were rarely studied. The hinge structure confers the antimicrobial peptides an improved structural flexibility, which may promote their disruptive effect on bacterial membrane or their binding efficiency to the intracellular targets, thus resulting in a higher antibacterial activity. Meanwhile, the hinge structure may reduce the structural rigidity, which may eliminate the cytotoxicity of antimicrobial peptides to eukaryotic cells. This article reviews the structural characteristics of the hinge structure, its effects on the biological activity of antimicrobial peptides and application in the molecular design, with the aim to provide a reference for the design and development of new antimicrobial peptides.