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A lightweight composite with outstanding damping effects and impact resistance is significant for the design of functional structures in advanced equipment, such as aircraft and space vehicles. In this paper, the mechanical properties of solution-blended graphene nanoplatelets (GNPs)/polyether-ether-ketone (PEEK) nanocomposites were characterized by both experimental and numerical methods. It can be found that the layer number and packing configuration of graphene layers are critical to the efficiency of energy dissipation in the composite, while a pack of six- layer graphene and the perpendicular arrangement to the shockwave direction provide the most outstanding energy dissipation ability. The reflection of shockwave caused by graphene reinforcements in the nanocomposite was found to be the dominating reason for the enhanced energy dissipation effect. Physical mechanisms of energy dissipation are investigated by a molecular modeling method to provide insights into the cross-scale design of graphene-reinforced nanocomposites as structural materials.

Aggregation-induced emission nanoparticles serve as promising fluorescence probes for multi-photon excitation microscopy due to the large absorption cross-section in the NIR-IIb region. Here we present organic AIE nanoparticles that feature a high absorption cross-section under three-photon excitation. We show that these enable ultra-deep NIR-IIa excited three-photon imaging in the in vivo mouse brain.

Photoluminescence (PL) of rare earth (RE) ions has been observed in RE ion-doped perovskite nanocrystals (PeNCs); however, the electroluminescence (EL) originating from the RE ions is still not ach...

Nanoparticle-assisted deep-tissue fluorescence imaging is of great significance to bioimaging and disease diagnosis. Through the combination of the electron donor triphenylamine and electron acceptor cyan, the compound 1,1-dicyano-2-phenyl-2-(4-diphenylamino)phenylethylene (DCPE-TPA, 1) was synthesized and exhibited an aggregation-induced emission (AIE) effect. Compound 1 can form three kinds of aggregation states: orange crystals (1OC, 578 nm, ΦF = 50.6%), red crystals (1RC, 613 nm, ΦF = 78.4%) and deep-red emissive amorphous solids (1Am, 667 nm, ΦF = 30.4%) with notable differences in their emission wavelengths and quantum yields. The DCPE-TPA molecules are encapsulated with a polymeric matrix of Pluronic F-127 to form nanoparticles (NPs) that exhibit intense three-photon fluorescence (3PF) in the deep-red region as well as high stability, good photostability and good biocompatibility. Under a 1560 nm fs laser, the DCPE-TPA NPs are further utilized for in vivo 3PF imaging of the vasculature in the brain of a mouse at various vertical depths, producing a penetration depth of 300 μm with a high spatial resolution of 1.8 μm and a high signal-to-background ratio (SBR) of 14. A high-resolution three-dimensional (3D) model of the vasculature beneath the skull could be reconstructed. It is worth mentioning that such a high quantum yield for the deep-red emission of a purely organic material has rarely been reported.

In vivo cortical optical imaging needs to overcome the scattering of skull. Compared to the traditional transcranial surgery-based open-skull glass window and thinned-skull preparation, chemical tissue optical clearing techniques can provide a skull-remained optical access to the brain while maintaining its original environment. However, previously demonstrated skull optical clearing windows could only maintain transparency for a couple of hours and hardly capable for high-resolution monitoring of awake animals. Here, we developed a convenient and easy-handling chronic skull optical clearing technique, named “Through-Intact-Skull (TIS) window”, which was compatible with long-term observation at high resolution, and yielded large imaging depth of 900 μm for cortical neurovascular visualization. In addition, our TIS window could monitor neuron activity in awake mice for a long term. Therefore, our bio-compatible and non-invasive TIS window is a new promising approach for intravital brain microscopy with great potential for basic research in neuroscience.

Laser speckle contrast imaging (LSCI) is a powerful tool to monitor blood flow distribution and has been widely used in studies of microcirculation, both for animal and clinical applications. Conventionally, LSCI usually works on reflective-detected mode. However, it could provide promising temporal and spatial resolution for in vivo applications only with the assistance of various tissue windows, otherwise, the overlarge superficial static speckle would extremely limit its contrast and resolution. Here, we systematically investigated the capability of transmissive-detected LSCI (TR-LSCI) for blood flow monitoring in thick tissue. Using Monte Carlo simulation, we theoretically compared the performance of transmissive and reflective detection. It was found that the reflective-detected mode was better when the target layer was at the very surface, but the imaging quality would rapidly decrease with imaging depth, while the transmissive-detected mode could obtain a much stronger signal-to-background ratio (SBR) for thick tissue. We further proved by tissue phantom, animal, and human experiments that in a certain thickness of tissue, TR-LSCI showed remarkably better performance for thick-tissue imaging, and the imaging quality would be further improved if the use of longer wavelengths of near-infrared light. Therefore, both theoretical and experimental results demonstrate that TR-LSCI is capable of obtaining thick-tissue blood flow information and holds great potential in the field of microcirculation research., The performance of novel transmissive-detected LSCI was systematically demonstrated through simulation and experiments. With such a simple system, individual vessel-resolution blood flow mapping and monitoring were realized on human hand.

Recently, various lanthanide ions (Ln3+) have been successfully doped into perovskite quantum dots (PQDs), and the quantum-cutting emission of 2F5/2-2F7/2 for Yb3+with a measurable inner efficiency of more than 100% has been discovered and applied as the luminescent converter of solar cells, which has opened a new branch for the application of PQDs. In this work, to further improve the quantum-cutting efficiency of Yb3+, the codoping and tridoping methods were used to improve the quantum-cutting emission of PQDs. The Yb3+-Ln3+ (Ln = Nd, Dy, Tb, Pr, Ce) pair-doped CsPbClxBryI3-x-y PQDs were fabricated, with all displaying excitonic emission, narrow-band emission of Ln3+ ions, and quantum-cutting emission of Yb3+ ions. It was interesting that Yb3+-Pr3+ as well as Yb3+-Ce3+ pairs could effectively sensitize the emission of Yb3+, owing to Pr3+ and Ce3+ ions offering intermediate energy states close to the exciton transition energy of the PQDs. After host composition optimization and tridoping investigation, overall emissions with a 173% photoluminescence quantum yield (PLQY) were obtained in the Yb3+-Pr3+-Ce3+-tridoped CsPbClBr2 PQDs. Then, the tridoped PQDs were designed as the down-converter for CuIn1-xGaxSe2 (CIGS) as well as the silicon solar cells, which leads to an enhancement of the power conversion efficiency (PCE) of as high as ∼20%. The modified CIGS was further employed to charge the smart mobile phone, which could largely shorten the charging time from 180 to 150 min. This finding is of great significant for expanding the application fields of the impurity-doped PQDs.

Employing lanthanide doped upconversion nanoparticles (UCNPs) as near-infrared absorbing photoactive materials is a feasible conception for constructing high efficient and stable narrowband wavelength-selective photodetectors, but limited by its upconversion luminescence efficiency. Herein, we experimentally and theoretically demonstrate upconversion luminescence (UCL) enhancement in monolayer UCNPs using plasmon semiconductor NPs (CsxWO3) and further explore its narrowband near-infrared photodetection application. The UCL improvement of 144 folds in CsxWO3/NaYF4/NaYF4:Yb3+, Er3+ hybrid was realized with the optimized spacer thickness (15 nm) and monolayer UCL. More than three orders enhancement was obtained via the semiconductor plasmon combined with core-shell UCNPs in both CsxWO3/NaYF4/monolayer-NaYF4:Yb3+, Er3+@NaYF4:Yb3+, Tm3+ and CsxWO3/NaYF4 /monolayer-NaYF4:Yb3+, Tm3+@NaYF4:Yb3+, Er3+. Interestingly, the higher enhancement of core's emissions was recorded in core-shell UCNPs by coupling with CsxWO3 NPs. The excitation field amplification dominates the high UCL enhancement, revealed by the UCL dynamics and the calculated electric field intensity. Finally, the high performance narrow photodetectors for 980 nm is constructed employing MAPbI3/CsxWO3/NaYF4/NaYF4:Yb3+, Er3+@NaYF4:Yb3+, Tm3+ hybrids, with narrow line width of 20 nm, high responsivity of 0.33 A/W, detectivity of 4.5 × 1010 Jones, and short response time of 180 ms, which is much better than the previous photodetectors. This finding provides keen approach for developing high efficient/performance UCNPs and narrowband photodetectors.

Due to the ultrathin structure, functional groups and excellent physical-chemical properties, Two-dimensional (2D) MXenes shows great potential for biomedical applications. Here, we prepared TiO2 inverse opal photonic crystals (IOPCs)/Ti3C2 quantum dots (QDs) composite film through the self-assembly method. Because of the widen absorption band of Ti3C2 QDs, TiO2 IOPCs/Ti3C2 composite film could have photocurrent effect from 280 to 900 nm, and the internal power conversion efficiency could reach to 26% at 350 nm. Owing to favourable energy levels, Ti3C2 QDs were formed the Type-II Heterojunction with TiO2, thus enabling directional transport charge for efficient charge separation. The Type-II Heterojunction photoelectrochemical (PEC) sensor consisting of TiO2/Ti3C2/Nafion electrode exhibited high stability, sensitivity, and selectivity for the detection of glutathione in buffered solution and cell extracts. Thus, the TiO2/Ti3C2/Nafion composite film provides a promising green electrode for sensitive PEC detection, which could realize some potential applications for disease early precaution and diagnose.

Pollution triggered by highly toxic heavy metal ions has become of worldwide critical concern; thus, it is urgent to develop an eco-friendly and nontoxic fluorescence probe for metal ions sensing. ...

NaLuF4: Yb3+/Er3+ phosphors are synthesized via a hydrothermal method. The photoluminescence properties of the phosphors are researched at a temperature range from 296 to 461 K under 1064 nm excitation. Fluorescence intensity ratio I/I0 shows a linear relationship with increasing the temperature from 296 to 420 K. The maximum sensitivity is obtained to be 0.0194 K-1 using non-contact ratiometric thermometer through multi-phonon assisted excitation.

Summary Advanced optical methods combined with various probes pave the way toward molecular imaging within living cells. However, major challenges are associated with the need to enhance the imaging resolution even further to the subcellular level for the imaging of larger tissues, as well as for in vivo studies. High scattering and absorption of opaque tissues limit the penetration of light into deep tissues and thus the optical imaging depth. Tissue optical clearing technique provides an innovative way to perform deep-tissue imaging. Recently, various optical clearing methods have been developed, which provide tissue clearing based on similar physical principles via different chemical approaches. Here, we introduce the mechanisms of the current clearing methods from fundamental physical and chemical perspectives, including the main physical principle, refractive index matching via various chemical approaches, such as dissociation of collagen, delipidation, decalcification, dehydration, and hyperhydration, to reduce scattering, as well as decolorization to reduce absorption., Graphical abstract, Subject areas: Optical Imaging; Biological Sciences; Research Methodologies; Biological Sciences Tools

Tissue optical clearing technique provides a prospective solution for the application of advanced optical methods in life sciences. This chapter firstly gives a brief introduction to mechanisms of tissue optical clearing techniques, from the physical mechanism to chemical mechanism, which is the most important foundation to develop tissue optical clearing methods. During the past years, in vitro and in vivo tissue optical clearing methods were developed. In vitro tissue optical clearing techniques, including the solvent-based clearing methods and the hydrophilic reagents-based clearing methods, combined with labeling technique and advanced microscopy, can be applied to image 3D microstructure of tissue blocks or whole organs such as brain and spinal cord with high resolution. In vivo skin or skull optical clearing, promise various optical imaging techniques to detect cutaneous or cortical cell and vascular structure and function without surgical window.

Aggregation-induced emission nanoparticles serve as promising fluorescence probes for multi-photon excitation microscopy due to the large absorption cross-section at NIR-IIb region. Here we present organic AIE nanoparticles that feature high aborption cross-section under three-photon excitation. We show that these enable ultra-deep NIR-IIa excited three-photon imaging in the in-vivo mouse brain.

International audience; In order to implement radiotherapy based on a laser accelerator, it is necessary to precisely control the spatial distribution and energy spectrum of the proton beams to meet the requirements of the radiation dose distribution in the three-dimensional biological target. A compact laser plasma accelerator has been built at Peking University, which can reliably generate and transport MeV-energy protons with a specified energy onto the irradiation platform. In this paper, we discuss several technologies for the accurate control of a laser-accelerated proton beam with large divergence angle and broad energy spread, including the determination of the beam source position with micron accuracy, a tuning algorithm for the transport line which we refer to as “matching-image-point two-dimensional energy analysis” to realize accurate energy selection, and the control of beam distribution uniformity. In the prototype experiment with low energy protons and 0.5-Hz irradiation rate, a tailored energy deposition is demonstrated, which shows the potential feasibility of future irradiation based on laser-accelerated proton beams.

Electromagnetic pulses (EMPs) produced by the interaction of a TW femtosecond laser with solid targets at the Compact Laser Plasma Accelerator (CLAPA) are measured and interpreted. The statistical results confirm that the intensities of the EMPs are closely related to both target material and thickness. The signal of the titanium target is more abundant than that of the copper target with the same thickness, and the intensity of EMP is positively correlated with the target thickness for aluminium foil. With the boosted EMP radiations, the energy of accelerated protons is also simultaneously enhanced. In addition, EMPs emitted from the front of the target exceed those from the rear, which are also pertinent to the specific target position. The resonant waveforms in the target chamber are analyzed using the fast Fourier transform, and the local resonance and the attenuation lead to changes of the frequency spectra of EMPs with variation of detecting positions, which is well supported by the modeling results. The findings are beneficial to gaining insight into the mechanism of EMP propagation in a typical target chamber and providing more information for EMP shielding design.

Quantum dots with narrow emission line width have persistently received attention for their applications in biological imaging, lasers and next-generation displays. We herein report a cation exchange assisted shelling approach changing the starting CdSe emitting cores into new ZnCdSe alloy emitting cores and finally ZnCdSe/ZnSe core/shell QDs. The resulting ZnCdSe/ZnSe QDs exhibit an emission line width as narrow as 17.1 nm with a near-unity photoluminescence quantum yield and a single emission channel. We anticipate that our study on a cation exchange assisted synthetic route for controlling the emission line widths of the QDs could be extended to high-quality green and blue ones beyond currently achieved.

Skull optical clearing window permits us to perform in vivo cortical imaging without craniotomy, but mainly limits to visible (vis)-near infrared (NIR)-I light imaging. If the skull optical clearing window is available for NIR-II, the imaging depth will be further enhanced. Herein, we developed a vis-NIR-II skull optical clearing agents with deuterium oxide instead of water, which could make the skull transparent in the range of visible to NIR-II. Using a NIR-II excited third harmonic generation microscope, the cortical vasculature of mice could be clearly distinguished even at the depth of 650 μm through the vis-NIR-II skull clearing window. The imaging depth after clearing is close to that without skull, and increases by three times through turbid skull. Furthermore, the new skull optical clearing window promises to realize NIR-II laser-induced targeted injury of cortical single vessel. This work enhances the ability of NIR-II excited nonlinear imaging techniques for accessing to cortical neurovasculature in deep tissue.

Stimulated emission depletion (STED) nanoscopy is a typical super-resolution imaging technique that has become a powerful tool for visualizing intracellular structures on the nanometer scale. Aggregation-induced emission luminogens (AIEgens) are ideal fluorescent agents for bioimaging and have been widely used for organelle targeting, cellular mapping and tracing. Since AIEgens generally have a large Stokes’ shift, which is beneficial for restraining the fluorescence background induced by the STED light, as well as high photobleaching resistance in their nanoaggregate states, which provides the potential for long-term imaging under a STED beam with high power density, they are ideal fluorescent agents for STED nanoscopy. The STED efficiency of aggregated TPA-T-CyP could reach more than 80%, and the dynamic mitochondrial visualization was achieved on the nanometer scale. Their moving, fission and fussion of mitochondria was clearly observed with a lateral spatial resolution of 74 nm.

Fabrication of nanoscale materials with desirable morphology and surface properties becomes more urgent when constructing hybrid nanocrystals with multiple functionalities. Here, we report a facile measure to control the outer layer growth direction combining with coprecipitation and thermal decomposition method for constructing a series of heterogeneous core/shell structured NaLnF4 nanocrystals, involving NaYF4 and NaNdF4 material. Our investigations suggest that it is feasible to control over the outer layer growth orientation by combining the two traditional methods.

We propose a broadband and high-efficiency four-wave-mixing wavelength converter based on parallel-cascaded micro-ring resonators (PCMRRs). By optimizing the distance between the mutually uncoupled ring resonators, we demonstrate that the PCMRR has a transmission spectrum with interleaved narrow and broad passbands. Broadband and high-efficiency wavelength conversion can be achieved by placing the pump and the signal in the narrow and broad passbands, respectively. We experimentally demonstrate a 25-GHz bandwidth wavelength converter based on optimally designed 3-ring PCMRR. Compared with the conventional single-ring-resonator-based wavelength converter with the same bandwidth, there is a 15-dB enhancement of conversion efficiency for the 3-ring PCMRR when the input pump power is 10 dBm.

The influence of nanocrystalline CoNiFeAl0.4Ti0.6Cr0.5 high-entropy alloy (HEA) particles addition on the microstructure and mechanical properties of SiCp/7075Al composites was investigated systematically. The CoNiFeAl0.4Ti0.6Cr0.5 high-entropy alloy was prepared by mechanical alloying, and the (5 vol% HEAp + 40 vol% SiCp)/7075Al (HEA-7075Al) and 45 vol% SiCp/7075Al (SiC-7075Al) composites were subsequently fabricated by squeeze casting. The HEA particles were well retained in the Al matrix and remained nanocrystalline following the squeeze casting and heat treatment process, which indicated that the CoNiFeAl0.4Ti0.6Cr0.5 high-entropy alloy has the advantage of sluggish diffusion behavior and thermal stability. The time for the HEA-7075Al composite reaching the aged-peak period (19.5 h) was slightly longer than that of the SiC-7075Al composite (15 h), indicating that the HEA particles addition has postponed the aging process, which can be ascribed to the decrease of dislocation density in the Al matrix, evaluated from XRD. Additionally, in contrast to the SiC-7075Al composite, the HEA-7075Al composite exhibits higher strength, better plasticity and higher modulus with the average values of 712 MPa, 0.82% and 171 GPa, respectively, which is the results of the good interface between HEA particles and Al matrix, high strength nanocrystalline HEA particles and proper dislocation density present in Al matrix.

Monoclinic phase Gd2(MoO4)3: Yb3+/Er3+ phosphor is synthesized via a simple sol-gel method. The XRD result reveals that the phosphor possesses monoclinic structure with space group C2/c(15). Under the excitation of a 980 nm laser, its emission spectra shows remarkably intense green and negligible red emissions, which are all two-photon process. By investigating effect of temperature on green emission of the sample, the competition between the thermal agitation and non-radiative relaxation of 2H11/2 level can be found, which is verified by the measurement of lifetime. In addition, the sensitivity of optical thermometry is studied based on the fluorescence intensity ratio technique through infrared excited green upconversion. The maximum sensitivity is found to be about 0.02574 K−1 at 510.2 K, suggesting that the phosphor can be used as an excellent material for optical temperature sensing.

CsPbX3 (X = Cl, Br or I) perovskite quantum dots (PQDs) have attracted tremendous attention due to their extraordinarily excellent optical properties. However, there is still an obstacle for their bio-application, which is limited by their water-instability. In this work, we have designed a novel visible light triggered photoelectrochemical (PEC) sensor for dopamine (DA) based on CsPbBr1.5I1.5 PQD immobilized three-dimensional (3D) TiO2 inverse opal photonic crystals (IOPCs). Supported by the TiO2 IOPCs, the water-stability of the PQDs as well as that of the PEC sensor was considerably improved. Furthermore, employed as a photoactive material in PEC sensor, CsPbBr1.5I1.5 PQDs can expand the photocurrent response of the PEC sensor to the whole visible region. In addition, the modulation of the photonic stop band effect of TiO2 IOPCs on the incident light and the emission of PQDs could further enhance the photocurrent response. Such a PEC sensor demonstrates sensitive detection of DA in phosphate buffer saline solution and serum, with a good linear range from 0.1 μM to 250 μM and a low detection limit of approximately 0.012 μM. Our strategy opens an alternative horizon for PQD based PEC sensing, which could be more sensitive, convenient and inexpensive for clinical and biological analysis.

Luminescence concentration quenching, mainly due to a cross relaxation (CR) process between lanthanide ions (Ln3+), widely occurs in Ln3+ doped luminescent materials, setting a limit in the dopant content of Ln3+ emitters to withhold the brightness. Here, we introduced Na+ ions into the CaF2 host lattice codoped with Nd3+ emitters that alleviates concentration quenching greatly. And we show that the optimal dopant concentration of Nd3+ in colloidal CaF2:Nd nanoparticles increased from 10 to 30 mol%, resulting in an ∼32 times near-infrared (NIR) (1052 nm) brightness under 800 nm laser irradiation. Our mechanistic investigation suggests that the enhancement of NIR photo-luminescence (PL) could be attributed to not only the increasing crystallinity of nanoparticles but also the reducing concentration quenching of Nd3+ by improving the dopant distribution of Nd3+ ions in the CaF2 lattice, as evidenced by the high angle annular dark field images. These result in the optimal concentration increase to produce brightness enhancement greatly. This strategy can be utilized for other Ln3+ doped CaF2 based nanomaterials for bio-imaging.

Fluorescent carbon dots (FCDs) have attracted tremendous attention in biological applications. The short-wave infrared (SWIR, 900–1700 nm) spectral range is considered as a novel optical tissue window due to low photon scattering. In this work, we investigated the fluorescence characteristics of FCDs based on the SWIR spectral range. SWIR emissions were observed from FCDs for the first time, when long-wavelength excitation (e.g. longer than 731 nm) was adopted. Wavelength-tunable two-photon fluorescence could also be obtained from the FCDs, under 1000–1560 nm SWIR femtosecond (fs) excitation. Interestingly, when an fs excitation wavelength as long as 1560 nm was adopted, two typical nonlinear optical signals, namely two-photon fluorescence and third harmonic generation (THG), could be observed. Based on the one-photon SWIR fluorescence, FCDs were successfully utilized for in vivo sentinel node mapping and tumour imaging. Under SWIR fs excitation, FCD-assisted two-photon fluorescence microscopy realized deep-tissue imaging of zebrafish embryos and the brain neuron networks of mice. SWIR excited and emitting FCDs have potential as fluorescent probes for deep-tissue and high-contrast functional bioimaging and related applications in the future.

With the advantages of high resolution and deep penetration depth, two-photon excited NIR-II (900–1880 nm) fluorescence (2PF) microscopic bioimaging is promising. However, due to the lack of imaging systems and suitable probes, few such works, to our best knowledge, were demonstrated utilizing NIR-II excitation and NIR-II fluorescence simultaneously. Herein, we used aqueously dispersible PbS/CdS quantum dots with bright NIR-II fluorescence as the contrast agents. Under the excitation of a 1550 nm femtosecond (fs) laser, they emitted bright 2PF in the NIR-II region. Moreover, a 2PF lifetime imaging microscopic (2PFLIM) system was implemented, and in vivo 2PFLIM images of mouse brain blood vessels were obtained for the first time to our best knowledge. To improve imaging speed, an in vivo two-photon fluorescence microscopy (2PFM) system based on an InGaAs camera was implemented, and in vivo 2PFM images of QDs-stained mouse brain blood vessels were obtained.

We propose a monolithic distributed Bragg reflector (DBR) integrated photodiode using a tapered waveguide with InP and polymer cladding layers for achieving a high efficiency bandwidth product. In the proposed photodiode, a DBR mirror is formed at the end of the waveguide, thereby increasing the effective absorption length of the device. Furthermore, to reduce the coupling loss, the InP and polymer cladding layers are formed under and on top of the core layer, respectively. Consequently, the mutual tradeoff between the bandwidth and quantum efficiency of the photodetector could be alleviated.

Quantum dots with single PL decay dynamics were promising for their applications in QD-based light-emitting devices. We here report an approach to synthesize high quality green emitting quaternary alloyed CdSeZnS quantum dots (QDs) with a hot-injection method. The quantum yield (QY) of as-synthesized ZnCdSSe QD cores is up to 84% with single-exponential PL decay dynamics. After overcoating 4 mono-layers (MLs) ZnS on the ZnCdSSe cores, the resultant ZnCdSSe/ZnS QDs reaches a PL QY as high as 96% at 520 nm and narrow emission spectra (full width at half maximum, FWHM

Laser-accelerated ion beams (LIBs) have been increasingly applied in the field of material irradiation in recent years due to the unique properties of ultra-short beam duration, extremely high beam current, etc. Here we explore an application of using laser-accelerated ion beams to prepare graphene. The pulsed LIBs produced a great instantaneous beam current and thermal effect on the SiC samples with a shooting frequency of 1 Hz. In the experiment, we controlled the deposition dose by adjusting the number of shootings and the irradiating current by adjusting the distance between the sample and the ion source. During annealing at 1100 °C, we found that the 190 shots ion beams allowed more carbon atoms to self-assemble into graphene than the 10 shots case. By comparing with the controlled experiment based on ion beams from a traditional ion accelerator, we found that the laser-accelerated ion beams could cause greater damage in a very short time. Significant thermal effect was induced when the irradiation distance was reduced to less than 1 cm, which could make partial SiC self-annealing to prepare graphene dots directly. The special effects of LIBs indicate their vital role to change the structure of the irradiation sample.

Herein, we propose a monolithic reflector-integrated waveguide photodetector with optical isolation between photosensitive mesa and N-contact mesa for achieving a high efficiency bandwidth product. In the proposed photodetector, the photosensitive mesa is optically isolated but electrically connected with the N-contact mesa; this is achieved by etching a portion of the core layer to form a groove on each side of the photosensitive mesa, enhancing the binding of the waveguide to optical power. Furthermore, a mesa is formed separate from the N-contact mesa at the end of the waveguide, and the metal film is deposited to act as a mirror, thereby increasing the effective absorption length of the device. Consequently, the mutual tradeoff between the bandwidth and quantum efficiency of the photodetector could be alleviated.

The ability to modulate the intensity of electromagnetic field by semiconductor plasmon nanoparticles is becoming attractive due to its unique doping-induced local surface plasmon resonance (LSPR) effect that is different from metals. Herein, we synthesized mCu2–xS@SiO2@Y2O3:Yb3+/Er3+ core–shell composites and experimentally and theoretically studied the semiconductor plasmon induced up-conversion enhancement and obtained 30-fold up-conversion enhancement compared with that of SiO2@Y2O3:Yb3+/Er3+ composites. The up-conversion enhancement was induced by the synthetic effect: the amplification of the excitation field and the increase of resonance energy transfer (ET) rate from Yb3+ ions to Er3+ ions. The experimental results were analyzed in the light of finite-difference time-domain (FDTD) calculations, confirming the effect of the amplification of the excitation field. In addition, up-conversion luminescence (UCL) spectra, up-conversion enhancement, and dynamics dependent on concentration (Yb3+ and Er3+ i...

Although lanthanide doped luminescent materials have been extensively investigated, a quantitative analysis of how temperature affects upconversion luminescence is still incomplete. The Gd2(MoO4)3:Er3+/Yb3+ phosphor is synthetized by sol-gel method. Based on the absorption spectra of Er3+ ions, J-O intensity parameters and radiative transition probabilities are computed to estimate the optical properties. In view of ion-phonon interaction, the phonon-assisted energy transfer and multiphonon relaxation are responsible for the temperature dependent luminescence. Additionally, cross relaxation probability for 4I11/2+4I11/2→4I15/2+4F7/2 is determined to be 240 s−1 through quantitative simulation of ion-ion interaction. These meaningful results are of vital values for the field of laser crystal and optical temperature sensing.

We developed a wideband transverse magnetic (TM) −reflected polarizer composed of BK7 prism and Ag/Cr/TiO2 film. Based on the polarization-dependent loss of coupled plasmon-waveguide resonance (CPWR), BK7 prism/Ag/Cr/TiO2/air layered structure can reflect the TM-components of lightwave and severely attenuate the transverse electric (TE) −components in a wavelength range from 600 nm to 900 nm at incident angles greater than the critical angle of total reflection. In terms of its practical application, a compact, low cost surface plasmon resonance (SPR) configuration with an integrated polarizer for wavelength modulation is presented and experimentally demonstrated.

The authors describe a new phosphor of the composition Gd2(WO4)3:0.3%Ho/0.5%Tm/15%Yb that displays distinctly improved sensitivity to temperature (T) due to non-thermally coupled energy levels of Ho(III) and Tm(III) ions. Under 980 nm excitation, the upconverted blue (peaking at 473 nm), green (540 nm) and red (655 and 700 nm) fluorescences exhibit T-dependent luminescence in the 295 to 595 K range. The T sensing capability was investigated by using a ratiometric (2-wavelength) technique. The maximum sensitivity to T is found to be 26.14 × 10−3 K−1 at 595 K based on the red [Tm(III)] and green [Ho(III)] emissions. The colors of the phosphor are located in the white region of the CIE diagram in the whole T-range which also makes it suitable for use in white displays.

Photon upconversion (UC) is an attractive strategy to substantially enhance the power conversion efficiency (PCE) of solar cells via upconverting unavailable near-infrared sunlight to available visible light. However, to date, it is almost infeasible to achieve effective PCE improvement of solar cells with the assistance of UC materials, limited by their poor UC efficiency and extremely weak and narrowband near-infrared absorption. Here, we demonstrate the efficient photon energy UC in semiconductor plasmon mCu2−xS@SiO2@Er2O3 (mCSE) nanocomposites, where the broadband semiconductor plasmon (800–1600 nm) of mCu2−xS serves as an antenna to sensitize UC of Er2O3 nanoparticles. The overall upconversion luminescence (UCL) of the composites was dramatically enhanced by a factor of ∼1000, with a maximal inner quantum efficiency of 14.3%. The excitation range was expanded, ranging from 800 to 1600 nm. As a proof-of-concept, the highly efficient mCSE nanocomposites were utilized to improve the PCE of perovskite solar cells (PSCs). The expansion of the near-infrared response (800–1000 nm) and considerable improvement of the PCE were obtained, with an optimum PCE of 17.8%. The mCSE composites in PSCs enhanced the photocurrent via electron transfer from oxygen defects to the conduction band of TiO2 under irradiation of one sunlight. Under irradiation of 15 suns, the electron transfer and reabsorption of UCL both contributed to the enhancement of PCE. Our work can provide an insightful thought on boosting UC efficiency as well as broadening the PCE of PSCs.

In this paper, we have synthesized erbium and ytterbium codoped sodium gadolinium fluoride (NaGdF4:Yb/Er) nanophosphors (NPs), aiming to extend the solar light harvest of PTB7 from visible into near-infrared. Evidence shows that Yb concentration plays an important role in upconversion, because it can inhibit the back energy transfer process and absorb considerable low-energy photons. Subsequently, NaGdF4:Yb/Er NPs have been incorporated into the photocatalytic titania (TiO $_2$ ) nanoparticle layer to probe into electron transfer dynamics, and the photovoltaic performance of the assembled solar cells has been explored. The results show that NaGdF4:Yb/Er NPs excited at 976 nm present green and red emissions. After interfacing with bare or NP-doped electron donor TiO $_2$ , the lifetime of the emerged electron transfer has been shortened from 840 to 466 ps, and correspondingly, the electron transfer rate outstrips that of the bare TiO $_2$ by a factor of 2.6. Consequently, an efficiency enhancement has been obtained with power conversion efficiency increasing to 3.61% from 2.81% of pure TiO $_2$ /PTB7. This work provides an efficient and facile approach to enhance the device performance by the codoping of robust rare-earth ions to widen the harvesting range of solar spectrum, boost electron transfer rate, and eventually strengthen the device performance.

Two-photon excited fluorescence microscopy and nanoparticle-assisted photodynamic therapy (PDT) are two important areas in biomedical research, and their combination can be more beneficial. A type of red emissive photosensitizer (PS) with aggregation-induced emission (AIE) features, which is called tetraphenylethylene (TPE-red), was synthesized and further encapsulated with poly(styrene-co-maleic anhydride) (PSMA) to form nanoparticles. Two-photon fluorescence, as well as two-photon excited reactive oxygen species (ROS) generation by TPE-red–PSMA nanoparticles, was characterized. A large two-photon absorption cross-section was observed at 1040 nm with a femtosecond (fs) laser. PDT via two-photon excitation was well realized on tumor cells, using TPE-red–PSMA nanoparticles as PSs under 1040 nm fs laser excitation. Based on our study, we believe that two-photon excited PDT with AIE-active PSs has great potential applications in deep tissue imaging-guided therapy.

Compared with visible light, near-infrared (NIR) light has deeper penetration in biological tissues. Three-photon fluorescence microscopy (3PFM) can effectively utilize the NIR excitation to obtain high-contrast images in the deep tissue. However, the weak three-photon fluorescence signals may be not well presented in the traditional fluorescence intensity imaging mode. Fluorescence lifetime of certain probes is insensitive to the intensity of the excitation laser. Moreover, fluorescence lifetime imaging microscopy (FLIM) can detect weak signals by utilizing time-correlated single photon counting (TCSPC) technique. Thus, it would be an improved strategy to combine the 3PFM imaging with the FLIM together. Herein, DCDPP-2TPA, a novel aggregation-induced emission luminogen (AIEgen), was adopted as the fluorescent probes. The three-photon absorption cross-section of the AIEgen, which has a deep-red fluorescence emission, was proved to be large. DCDPP-2TPA nanoparticles were synthesized, and the three-photon fluorescence lifetime of which was measured in water. Moreover, in vivo three-photon fluorescence lifetime microscopic imaging of a craniotomy mouse was conducted via a home-made optical system. High contrast cerebrovascular images of different vertical depths were obtained and the maximum depth was about 600 [Formula: see text]m. Even reaching the depth of 600 [Formula: see text]m, tiny capillary vessels as small as 1.9 [Formula: see text]m could still be distinguished. The three-photon fluorescence lifetimes of the capillaries in some representative images were in accord with that of DCDPP-2TPA nanoparticles in water. A vivid 3D reconstruction was further organized to present a wealth of lifetime information. In the future, the combination strategy of 3PFM and FLIM could be further applied in the brain functional imaging.

Nonlinear optical microscopy has become a powerful tool in bioimaging research due to its unique capabilities of deep optical sectioning, high-spatial-resolution imaging, and 3D reconstruction of biological specimens. Developing organic fluorescent probes with strong nonlinear optical effects, in particular third-harmonic generation (THG), is promising for exploiting nonlinear microscopic imaging for biomedical applications. Herein, a simple method for preparing organic nanocrystals based on an aggregation-induced emission (AIE) luminogen (DCCN) with bright near-infrared emission is successfully demonstrated. Aggregation-induced nonlinear optical effects, including two-photon fluorescence (2PF), three-photon fluorescence (3PF), and THG, of DCCN are observed in nanoparticles, especially for crystalline nanoparticles. The nanocrystals of DCCN are successfully applied for 2PF microscopy at 1040 nm NIR-II excitation and THG microscopy at 1560 nm NIR-II excitation, respectively, to reconstruct the 3D vasculature of the mouse cerebral vasculature. Impressively, the THG microscopy provides much higher spatial resolution and brightness than the 2PF microscopy and can visualize small vessels with diameters of ≈2.7 µm at the deepest depth of 800 µm in a mouse brain. Thus, this is expected to inspire new insights into the development of advanced AIE materials with multiple nonlinearity, in particular THG, for multimodal nonlinear optical microscopy.

Nonlinear optical microscopy has become a powerful tool in bioimaging research due to its unique capabilities of deep optical sectioning, high spatial resolution imaging and three-dimensional reconstruction of biological specimens. Developing organic fluorescent probes with strong nonlinear optical effects, in particular third-harmonic generation (THG), is promising for exploiting nonlinear microscopic imaging for biomedical applications. Herein, we succesfully demonstrate a simple method for preparing organic nanocrystals based on an aggregation-induced emission (AIE) luminogen (DCCN) with bright near-infrared emission. Under femtosecond laser excitation, the high-order nonlinear optical effects of DCCN were studied in three distinct systems, including monomolecules in solution, amorphous nanopaticles, and crystaline nanopaticles. Results revealed aggregation-induced nonlinear optical (AINLO) effects, including two-photon fluorescence (2PF), three-photon fluorescence (3PF) and THG, of DCCN in nanopaticles, especially for the crystaline nanopaticles. Taking advantage of the strong 2PF and THG properties, the nanocrystals of DCCN have been successfully applied for 2PF microscopy at 1040 nm NIR-II excitation and THG microscopy at 1560 nm NIR-II excitation, respectively, to reconstruct the 3D vasculature of the mouse cerebral vasculature. Impressively, the THG microscopy could provide much higher spatial resolution and brightness than the 2PF microscopy and could visualize small vessels with diameters of ~2.7 μm at deepest depth of 800 μm in mouse brain, which is among the largest penetration depth and best spatial resolution of in vivo THG vasculature imaging. Thus, this is expected to inspire new insights into development of advanced AIE materials with multiple nonlinearity, in particular THG, for multimodal nonlinear optical microscopy.

A compact laser plasma accelerator (CLAPA) that can stably produce and transport proton ions with different energies less than 10 MeV, $l1%$ energy spread, several to tens of pC charge, is demonstrated. The high current proton beam with continuous energy spectrum and a large divergence angle is generated by using a high contrast laser and micron thickness targets, which later is collected, analyzed and refocused by an image-relaying beam line using a combination of quadrupole and bending electromagnets. It eliminates the inherent defects of the laser-driven beams, realizes precise manipulation of the proton beams with reliability, availability, maintainability and inspectability (RAMI), and takes the first step towards applications of this new generation of accelerator. With the development of high-rep rate Petawatt (PW) laser technology, we can now envision a new generation of accelerator for many applications in the near future soon.

The development of blue quantum dot light-emitting diodes (QLEDs) lags far behind that of the red and green ones, which hinders the practical commercialization of QLEDs. Balancing the charge transfer still remains a challenging task, because blue QD emitters have a deeper valence band (VB) that creates a great injection barrier impeding the hole transfer. Herein, we demonstrate that the charge transfer balance can be improved by using a tert-butyldimethylsilyl chloride-modified poly(p-phenylene benzobisoxazole) (TBS-PBO) blocking layer. The TBS-PBO acts well in blocking excess electron injection and preserving the emission efficiency of the QD emitter. Compared to the insulating blocking layers, TBS-PBO has good conductivity, thus keeping the current density at a high level. Our device delivers a notable luminance of 4635 cd m-2 at an external quantum efficiency (EQE) maximum of 17.4%. To the best of our knowledge, the luminance with EQE > 17% is the highest one to be reported for blue QLEDs.

Quantum dots (QDs) have become promising light sources for next-generation lightings and displays. Realizing their applications in optoelectronic devices requires that QDs should retain their superior optical performances in condense QD films. However, most QD systems suffer intense photoluminescence (PL) quenching after film formation. Here, we report device-grade thick-shell CdZnSe/ZnSe/ZnS QDs with near-unity PL quantum yield (QY) in QD solution and 82% PL QY in QD film. We demonstrate that the thick shell functions well in restraining undesired inter-dot energy transfer by separating the emitting cores in condense QD film, and therefore preserving their superior emission properties. White light-emitting diodes (WLEDs) integrated with 5 different CdZnSe/ZnSe/ZnS QDs cover the visible spectrum, delivering a color rendering index (CRI) Ra as high as 91.4, a luminous efficiency (LE) of 68.5 lm/W and a warm bright sun light with correlated color temperature (CCT) of 4138 K. In particular, the champion CdZnSe/ZnSe/ZnS based WLED exhibits a special color index R9 as high as 93.1.

Aromatic polyamide fiber becomes the most important material for ballistic protection purposes because of the high modulus and strength from the 1960s. To obtain an insightful understanding of the mechanical deformation of Kevlar, a detailed multiscale model is developed in this paper based on the structures of Kevlar from molecular scale to macroscopic scale. By analyzing the molecular structures of Kevlar, the high modulus of Kevlar fibers can be attributed to the high stiffness of aromatic polyamide chains and the massively distributed hydrogen bonds in the material. The damage initiation and evolution in Kevlar fiber can be captured at the microfibril scale. It can be found that the material strength in the grain boundary regions is only 1.9 GPa, resulting in much lower strength of the whole Kevlar fiber (2.5–3.3 GPa), compared to the theoretical strength of the aromatic polyamide crystals (>30 GPa). The structural parameters of Kevlar fiber (pleated width, misorientation angle and skin thickness) are also studied to understand the contribution of these parameters to the stretching behavior of a Kevlar Bundle, which is significant to the future improvement of aromatic polyamide fibers for reinforcement purposes in advanced equipment.

Filterless narrowband near-infrared photodetectors (NIRPDs) offer significantly reducing cost and the system volume for various applications, but limited by the poor photosensitivity. Herein, we theoretically and experimentally demonstrate a novel class of sensitive filterless NIRPDs in CsPbF3: Zn2+-Yb3+- Tm3+ (or Er3+) perovskite nanocrystals (PeNCs)/Au nanorods (NRs) array hybrid via direct photon-electric upconverion (UC) from ground state of Yb3+- Tm3+ (or Er3+) to conduction band of PeNCs. It shows the selectively spectral photodetection at 980-nm NIR region with all full-width at half-maximum of 20 nm, high responsivity of 106 A/W, detectivity of 1.52 × 1012 Jones, and external quantum efficiency of 135%. The excellent performance can be mainly ascribed to (1) direct photon-electric UC mechanism; (2) the reduced trapping-center density, high carrier mobility, and increased extraction and separation efficient of election-hole pairs of PeNCs; (3) localized surface plasmon enhancement. Our findings open the exciting potential for developing the next-generation narrow NIRPDs.

Hexagonal phase NaLuF4:Yb3+/Er3+ nanorods were synthesized hydrothermally. An analysis of the intense green upconversion emissions at 525 nm and 550 nm in hexagonal phase NaLuF4:Yb3/+Er3+ nanorods under excitation power density of 4.2 W/cm2 available from a diode laser emitting at 976 nm, have been undertaken. Fluorescence intensity ratio (FIR) variation of temperature-sensitive green upconversion emissions at 525 nm and 550 nm in this material was recorded in the physiological range from 295 to 343 K. The maximum sensitivity derived from the FIR technique of the green upconversion emissions is approximately 0.0044 K−1. Experimental results implied that hexagonal phase NaLuF4:Yb3/+Er3+ nanorods was a potential candidate for optical temperature sensor.