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Mid-infrared (mid-IR) pulse modulation components are extremely limited and are not very effective. By fabricating a novel broadband two-dimensional (2D) material, indium selenide (InSe), and adopting it as the passive saturable absorber (SA), we demonstrate a stable Q-switched Er-ZBLAN fiber laser at 2.8 μm. The stable Q-switching pulses can be maintained from the lasing pump threshold to the maximum pump power of 8.69 W, with the pulse repetition frequency ranging from 70.4 kHz to 253.2 kHz and the shortest pulse width of 423.2 ns. The obtained maximum value of average output power in this experiment is 712 mW, and the corresponding maximum pulse energy and peak power are 2.81 μJ and 5.71 W, respectively. The signal-to-noise ratio (SNR) of the laser output is 43.66 dB, which is larger than the majority of the passively Q-switched mid-IR fiber lasers reported so far. Besides, the nonlinear optical response at a mid-IR wavelength of ∼2.8 μm is also investigated. The experimental results demonstrate that the InSe material has great potential in mid-infrared pulse modulation and generation, and its performance can be comparable or even superior to the widely used SESAM.

Tellurene, as a typical non-layered two-dimensional (2D) material, has attracted a lot of attention due to its superior properties such as fast photoconductivity, high thermoelectricity, large piezoelectricity, and excellent nonlinear optical response. Here, a unique, simple, and rapid solution method for the synthesis of high-quality hexagonal Te nanosheets with large area has been proposed. In the presence of polyvinylpyrrolidone (PVP) as a surfactant, the raw material, i.e., tellurium sodium hydride (NaHTe) was rapidly oxidized by O2 in ethanol solution to obtain the hexagonal Te nanosheets with a size of 5–11 μm and a thickness of 50–170 nm. In addition, the experimental results demonstrated that the prepared hexagonal Te nanosheets possessed good optical absorption and exhibited good photoresponse and stability as a photoanode material in a photoelectrochemical (PEC)-type photodetector. Meanwhile, this material also showed excellent nonlinear absorption properties, and the erbium-doped fiber ring laser with the Te nanosheets as a saturated absorption material successfully achieved mode-locking operation at 1550 nm. This work provides new ideas for the preparation of hexagonal Te nanosheets and their applications in optoelectronics and ultrafast photonics.

The well-formed high quality β-NaYF4:Er3+/Tm3+, Yb3+ microcrystals with near/mid-infrared (NIR/MIR) emission are synthesized by the solvothermal method. Obvious 1.4 μm, 1.8 μm emissions, and 1.5 μm emission are observed in as-prepared β-NaYF4:Tm3+, Yb3+ and β-NaYF4:Er3+, Yb3+ microcrystals, respectively. To obtain MIR emission, the as-prepared β-NaYF4:Er3+, Yb3+ microcrystals are heat-treated at different temperature schedule and atmosphere, it demonstrates there is great effect on the morphology and crystal structure when heat-treated at different temperature, while little effect under different heat-treated atmosphere. Subsequently, after heat-treatment at 575°C in air, owing to the efficient elimination of internal defects and partly surface hydroxyl/citrate groups, an obvious 2.7 μm MIR emission is successfully detected in heat-treated β-NaYF4:Er3+, Yb3+ microcrystals for the first time.

The blooming development of biomimetics has demonstrated infinite possibilities in providing solutions for our technical or engineering problems. Therefore, it makes sense to develop an efficient manufacturing system for biomimetic products to transfer biological techniques to engineering. Compared with conventional manufacturing, the decentralized one assisted by additive manufacturing brings the production process closer to the customized requirement of end users due to the accompanying manufacturing freedom in terms of both architecture coding and functionality distribution. Decentralized manufacturing is implemented through firstly deconstructing and analyzing the organism and subsequently establishing the manufacturing scheme. In this minireview, we take a bird's-eye view on the latest progress of biomimetic manufacturing through a decentralized and reverse perspective right from the selected characteristics of natural organisms, and call for a cooperation of digitization design and nanomaterial design. With further synergetic development of biomimetics, nanomaterial science and digitization-assisted additive manufacturing technology, it is anticipated that the decentralized approach will provide a shortcut towards a high-efficiency manufacturing way for biomimetic products.

Density functional theory calculations of the layer (L)-dependent electronic band structure, work function and optical properties of &beta, InSe have been reported. Owing to the quantum size effects (QSEs) in &beta, InSe, the band structures exhibit direct-to-indirect transitions from bulk &beta, InSe to few-layer &beta, InSe. The work functions decrease monotonically from 5.22 eV (1 L) to 5.0 eV (6 L) and then remain constant at 4.99 eV for 7 L and 8 L and drop down to 4.77 eV (bulk &beta, InSe). For optical properties, the imaginary part of the dielectric function has a strong dependence on the thickness variation. Layer control in two-dimensional layered materials provides an effective strategy to modulate the layer-dependent properties which have potential applications in the next-generation high performance electronic and optoelectronic devices.

Heterostructures comprising two-dimensional (2D) materials have attracted increasing attention in recent years due to their unique properties. Here, a 2D black phosphorous (BP)/MXene (Ti3C2) heterostructure is prepared by stacking BP and Ti3C2 using van der Waals forces. Ultraviolet–visible absorption spectra proved the excellent stability of the heterostructure in water and air. In addition, strong nonlinear properties (high modulation depth with small saturation intensity) are demonstrated through Z-scan measurements, indicating that the BP/Ti3C2 heterostructure has excellent potential as an optical switch. To illustrate the applicability of the BP/Ti3C2 heterostructure ultrafast photonics, its performance as a saturable absorber in an Er-doped mode-locked fiber laser is demonstrated, resulting in a 735 fs pulse duration at a center wavelength of 1559.8 nm. Furthermore, harmonic mode-locking was also achieved by increasing the pump power, yielding a peak repetition rate of 588 MHz. These results reveal that 2D BP/Ti3C2 heterostructures have significant potential application in ultrafast photonics.

Photothermal therapy (PTT) offers many advantages such as high efficiency and minimal invasiveness, but clinical adoption of PTT nanoagents have been stifled by unresolved concerns such as the biodegradability as well as long-term toxicity. Herein, poly (lactic-co-glycolic acid) (PLGA) loaded with black phosphorus quantum dots (BPQDs) is processed by an emulsion method to produce biodegradable BPQDs/PLGA nanospheres. The hydrophobic PLGA not only isolates the interior BPQDs from oxygen and water to enhance the photothermal stability, but also control the degradation rate of the BPQDs. The in vitro and in vivo experiments demonstrate that the BPQDs/PLGA nanospheres have inappreciable toxicity and good biocompatibility, and possess excellent PTT efficiency and tumour targeting ability as evidenced by highly efficient tumour ablation under near infrared (NIR) laser illumination. These BP-based nanospheres combine biodegradability and biocompatibility with high PTT efficiency, thus promising high clinical potential., Black phosphorus is a biodegradable 2D material that has attracted growing interest in biomedicine. Here, the authors carry out in vitro and in vivo experiments to demonstrate that nanospheres loaded with black-phosphorus quantum dots perform as promising phothermal cancer therapy agents.

Poly(vinylpyrrolidone)-encapsulated Bi2 Se3 nanosheets with a thickness of 1.7 nm and diameter of 31.4 nm are prepared by a solution method. Possessing an extinction coefficient of 11.5 L g(-1) cm(-1) at 808 nm, the ultrathin Bi2 Se3 nanosheets boast a high photothermal conversion efficiency of 34.6% and excellent photoacoustic performance. After systemic administration, the Bi2 Se3 nanosheets with the proper size and surface properties accumulate passively in tumors enabling efficient photoacoustic imaging of the entire tumors to facilitate photothermal cancer therapy. In vivo biodistribution studies reveal that they are expelled from the body efficiently after 30 d. The ultrathin Bi2 Se3 nanosheets have large clinical potential as metabolizable near-infrared-triggered theranostic agents.

Ultrasmall black phosphorus quantum dots (BPQDs) with an average size of 2.1 ± 0.9 nm are synthesized by using a solvothermal method in a N-methyl-2-pyrrolidone solution. Verified by femto-second laser Z-scan measurement, BPQDs exhibit excellent nonlinear optical response with a modulation depth of about 36% and a saturable intensity of about 3.3 GW cm−2. By using BPQDs as optical saturable absorber, the ultrashort pulse with a pulse duration of about 1.08 ps centered at a wavelength of 1567.5 nm is generated in mode-locked fiber laser. These results suggest that BPQDs may be developed as another kind of promising nanomaterial for ultrafast photonics.

A titanium sulfonate ligand is synthesized for surface coordination of black phosphorus (BP). In contrast to serious degradation observed from the bare BP, the BP after surface coordination exhibits excellent stability during dispersion in water and exposure to air for a long period of time, thereby significantly extending the lifetime and spurring broader application of BP.

2D silicon nanosheets (SiNSs) are promising materials for biomedicine but facile synthesis of SiNSs remains a challenge. Herein, by means of a sulfur-iodine co-assisted chemical vapor transport method, octahedron silicon (oct-Si) crystals with fully exposed {111} planes are prepared as precursors for efficient synthesis of SiNSs by facet-selective exfoliation. The 13 nm thick SiNSs have good biocompatibility and the sharp Raman scattering signal facilitates intracellular Raman imaging upon exposure to a near-infrared (NIR) laser. Furthermore, the SiNSs have excellent NIR photothermal characteristics such as a large extinction coefficient of 11.3 L g-1 cm-1 and high photothermal conversion efficiency of 21.4% at 1064 nm. In vitro experiments demonstrate superior NIR-II photothermal therapeutic effects in killing cancer cells. Comparing to conventional methods, the novel facet-selective cleavage strategy is more controllable and environmentally friendly boding well for the fabrication of non-van der Waals 2D materials. The multimodal photonic behavior also suggests large potential of the SiNSs pertaining to integrated multi-NIR biophotonic techniques using single nanomaterials.

The environmental instability and uneliminable electronic trap states in black phosphorus quantum dots (BPQDs) limit the optoelectronics and related applications of BPQDs. Here, fluorinated BPQDs (F-BPQDs) are successfully synthesized by using a facile electrochemical exfoliation and synchronous fluorination method. The F-BPQDs exhibit robust ambient stability and limited fluorination capability, showing a nonstoichiometric fluorination degree (DF) maximum of ≈0.68. Density functional theory calculations confirm that due to the edge etching effect of fluorine adatoms, the simulated F-BPQDs become structurally unstable when DF surpasses the limit. Furthermore, the trap states of BPQDs can be effectively eliminated via fluorination to obtain a coordination number of 3 or 5 for fluorinated and unfluorinated phosphorus atoms. The results reveal that the air-stable F-BPQDs exhibit fluorine defect-enhanced electronic tolerance, which is crucial for nanophotonics and nanoelectronics applications.

We demonstrated the enhanced second harmonic generation (SHG) from a single sodium niobate (NaNbO3) nanocrystal by approaching a metal tip on top of it. By scanning a laser-focused NaNbO3 nanocrystal with a gold-coated tip, the mapping of the enhanced SHG from the nanocrystal was obtained. We observed that the SHG of the single NaNbO3 nanocrystal was strongly enhanced with the gold-coated tip on the top of it. And the enhancement factor showed strong dependence on the excitation polarization and the excitation power. An over 12-fold tip enhancement was observed when the excitation power was 12 mW.

Non-agglomerated and uniform Eu3+-doped NaGdF4 nanocrystals were synthesized via a facile one-step precipitation method at room temperature. Under pulsed magnetic fields, the luminescence properties of the as-prepared samples have been recorded and discussed in detail. Particularly, “controllable eliminating luminescence” of 5D0–7F0 transition in Eu3+ was achieved during the magneto-optical interaction. Magnetic field assisted cross-relaxation of excited electrons was derived from Zeeman splitting of the higher 5D energy level, and the magnetic confinement of f electron wave functions was proposed which were responsible for the change in luminescence intensity with a variation of magnetic field strength. The characteristic variation of the emission band under pulsed magnetic fields promises an optical probe for magnetic field detection.

We synthesized NaNbO3 micro/nano-crystals with six morphologies and three different crystal structures using the hydrothermal method. Each single hexagonal NaNbO3 micro/nano-crystal (samples No. 1–3) exhibited a strong second-order nonlinear response. By calculating the average intensity and measuring the polarization response of each of these hexagonal crystals (samples No. 1–3), it was demonstrated that the same crystal structure displays a similar optical second harmonic generation (SHG) response. Furthermore, SHG was shown to be independent of the morphology and identical for similar crystals, which is expected for a volume effect with a second-order susceptibility tensor depending on the properties of the material. The optical SHG properties of these NaNbO3 micro/nano-crystals together with the previous related research suggest that these non-toxic crystals may find promising applications in biological imaging and related fields.

The reducing capability of two-dimensional black phosphorus is demonstrated. The high reducing ability and unique two-dimensional morphology of black phosphorus not only facilitate in situ synthesis of Au nanoparticles and BP@Au composites, but also enable multiscale control of local reduction of GO to reduced GO (rGO). The novel two-dimensional reductant has large potential in various in situ nanofabrication applications. Synthesis of various nano-sized materials generally involves chemical reduction with an extrinsic reductant. Here Prof. Xuefeng Yu, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, and co-workers have uncovered the reducing capability of black phosphorus (BP), a new 2D semiconductor material. It is demonstrated that the high reducing ability and unique 2D morphology of BP not only facilitate in situ synthesis of Au nanoparticles and BP@Au nanocomposites, but also enable multiscale control in local reduction of a graphene oxide to a reduced graphene oxide. The novel 2D reductant has large potential in various in situ nanofabrication applications and this study extends the application of 2D materials to new areas.

NIR luminescence phosphors Sr2CeO4:Yb3+, M+ (M+=Li+, Na+, K+) were synthesized by conventional solid-state method in the present paper. The prepared phosphors are characterized by XRD and fluorescence spectrometer. Under UV light excitation, the NIR emission intensity of Yb3+:2F5/2→2F7/2 around 1 μm of Sr2CeO4:Yb3+ is strengthened significantly by introducing appropriate alkali metal cations dopants (Li+, Na+, K+) into the crystalline lattice. The relevant mechanisms have been discussed in detail. The peculiar optical properties make Sr2CeO4:Yb3+, M+ (M+=Li+, Na+, K+) promising for potential application in the high efficiency silicon-based solar cells.

Novel up-conversion (UC) luminescent nanopowders, Sr2CeO4:Yb3+,Ln3+ (Ln = Er, Tm, Ho) were prepared with Pechini method. The Sr2CeO4:Yb3+,Ln3+ (Ln = Er, Tm, Ho) nanopowders had an orthorhombic crystal structure, and showed olive-like morphology with the length of about 260 nm and width of about 130 nm. Under 980 nm lazer excitation, the Sr2CeO4:Yb3+/Er3+, Sr2CeO4:Yb3+/Tm3+, and Sr2CeO4:Yb3+/Ho3+ nanophosphors exhibit strong green, blue, and green UC luminescence, respectively. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed.

In this work, we show here that the up-conversion luminescence of NaNbO3:Er3+/Yb3+ nano-materials can be modulated by magnetic field and a enhancement of up-conversion intensities by a factor of about 2 for Er3+:4S3/2 → 4I15/2 obtained at 30 T and about 5.4 for Er3+:4F9/2 → 4I15/2 obtained at 20 T. The increased up-conversion luminescence are mainly interpreted in terms of the enhanced non-radiation transition from 4I11/2 to 4I13/2 of Er3+ ions and the spin-orbital coupling (that is “mixing” effect) in crystal field by an external magnetic field. Meanwhile, we observed continuously spectra broadening with growing the magnetic field intensity, which is ascribed to the “mixing” effect induced by magnetic field and the difference of g factor of sub-bands. This bi-functional material with controllable optical-magnetic interactions has various potential applications, such as optical detection of magnetic field, etc.

The morphology of hexagonal phase NaYF4:Er3+ nanorods synthesized by hydrothermal method changed greatly after a continuing calcination, along with a phase transformation to cubic phase. Photoluminescence (PL) spectra indicated that mid-infrared (MIR) emission was obtained in both hexagonal and cubic phase NaYF4:Er3+ nanocrystals for the first time. And the MIR emission of NaYF4:Er3+ nanocrystals enhanced remarkably at higher calcination temperature. To prevent uncontrollable morphology from phase transformation, the cubic phase NaYF4:Er3+ nanospheres with an average size of ~100 nm were prepared via a co-precipitation method directly. In contrast, the results showed better morphology and size of cubic phase NaYF4:Er3+ nanocrystals have realized when calcined at different temperatures. And PL spectra demonstrated a more intense MIR emission in the cubic phase NaYF4:Er3+ nanocrystals with an increasing temperature. Besides, the MIR emission peak of Er3+ ions had an obvious splitting in cubic phase NaYF4. Therefore, cubic phase NaYF4:Er3+ nanospheres with more excellent MIR luminescent properties seems to provide a new material for nanocrystal-glass composites, which is expected to open a broad new field for the realization of MIR lasers gain medium.

Millimeter-scale 3D superlattice arrays composed of dense, regular, and vertically aligned gold nanorods are fabricated by evaporative self-assembly. The regular organization of the gold nanorods into a macroscopic superlattice enables the production of a plasmonic substrate with excellent sensitivity and reproducibility, as well as reliability in surface-enhanced Raman scattering. The work bridges the gap between nanoscale materials and macroscopic applications.

We have fabricated high quality NaNbO3:Eu3+ nano-crystals based on the Pechini sol-gel method and realized its magneto-optical effect under external pulsed magnetic field. Our results show that magnetic field can induce the suppression of luminescence, the splitting of peaks, and shifting of peak locations due to the expansion of electric dipole emission in Europium ions, and further demonstrate that the magnetic dipole emission plays an insignificant role in effect on the magnetic dipole emission for Eu3+:5 D 0 → 7 F 1, 5 D 0 → 7 F 3 transitions in NaNbO3:Eu3+ nano-crystals. These magnetic-optical interactions are attributed to the results of the Zeeman effect by high magnetic field that could result in the change of the symmetry of Eu3+ ions, and there is different sensitivity to changes of symmetry for Eu3+:5 D 0 → 7 F J (J = 1–4) transitions in NaNbO3 nano-crystals. This work might provide a viable magneto-optical approach in tuning the optical properties (luminescence intensity, peak location, profile, etc) of the rare-earth ions doped nano-particles.

2D black phosphorus (BP) nanomaterials are presented as a delivery platform. The endocytosis pathways and biological activities of PEGylated BP nanosheets in cancer cells are revealed for the first time. Finally, a triple-response combined therapy strategy is achieved by PEGylated BP nanosheets, showing a promising and enhanced antitumor effect.

High-yielded ultrathin MoS2 nanosheets (UMS) with thickness below 4 nm were successfully synthesized by a simple, cost-effective and reproducible solid-state reaction method. Significant reverse saturable absorption and nonlinear refraction responses of the UMS were measured by the z-scan experiment under femtosecond pulses at 800 nm. The figure of merit is calculated to be ~2.52 × 10−15 esu cm. Furthermore, optical limiting (OL) effects of the UMS were observed with low threshold FOL ~44 mJ/cm2. These results reveal that solid-state reaction is a feasible method for the fabrication of optical nanomaterials used in nanophotonic devices including optical limiter, which can be expanded to prepare other two-dimensional nanomaterials.

TiO2-based micro/nano fibres with secondary hierarchical structure have been extensively studied concerning a wide range of applications. However, simultaneous optimization of the flexibility and thermal stability of these materials still remains a big challenge. In this investigation, the successful fabrication and characterization of TiO2–SiO2 composite micron fibers with both high flexibility and excellent thermal stability are reported. Electrospun flexible SiO2 fibers were used as the scaffold for supporting TiO2 nanostructures. Three distinguished layers of porous SiO2, anatase TiO2 nanoparticle and rutile TiO2 nanorods were muffled over the SiO2 fibers stepwise, forming a unique core@multi-shell architecture with hierarchical structure. Such elaborately designed core@multi-shell TiO2–SiO2 fibers present high flexibility, excellent thermal stability, large specific surface area and high porosity. Moreover, they are easy to be patterned into nonwoven film with hierarchically porous structure, which is promising for many applications. We evaluate the water purification performance of the TiO2–SiO2 nonwoven film with Rhodamine B as a model organic pollutant. Efficient removal of Rhodamine B from water was implemented via simple filtration under UV irradiation, and regeneration of the photocatalytic functionality of the film from organic contamination was conveniently realized merely through calcination.