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Energy transfer has been proven to be an effective method to optimize optoelectronic conversion efficiency by improving light absorption and mitigating nonradiative losses. We prepared 2D/3D CsPbBr3 hybrid assemblies at different reaction temperatures using the hot injection method and found that the photoluminescence quantum yields (PLQYs) of these hybrids were greatly enhanced from 53.4% to 72.57% compared with 3D nanocrystals (NCs). Femtosecond transient absorption measurements were used to study the PLQY enhancement mechanisms, and it was found that the hot carrier lifetime improved from 0.36 to 1.88 ps for 2D/3D CsPbBr3 hybrid assemblies owing to the energy transfer from 2D nanoplates to 3D NCs. The energy transfer benefits the excited carrier accumulation and prolonged hot carrier lifetime in 3D NCs in hybrid assemblies, as well as PLQY enhancement in materials. [ABSTRACT FROM AUTHOR]

In semiconductor‐based microlasers, the generated excited carriers can affect both the optical absorption coefficient and refractive index, influencing the lasing behavior and device performance. In this study, the lasing behavior of individual MAPbBr3 microrods pumped by femtosecond laser pulses is investigated using an ultrafast optical Kerr gating technique. By analyzing the spectral and temporal evolution of the lasing behavior, it is found that the band‐filling (BF) effect can cause a significant change in the refractive index of the material, which results in an unfavorable red‐shift and broadening of the resonant modes, deteriorating the laser linewidth and quality factor. The hot carrier cooling process can provide a buffer for alteration of the energy level occupation state, resulting in a small transient refractive index change and slight red‐shift. These results offer insights into the lasing behavior driven by photogenerated carrier dynamics and provide an optimization strategy for semiconductor‐based microlasers. [ABSTRACT FROM AUTHOR]

Nonlinear optical limiting (OL) properties of carboxyl-functionalized Ti3C2 nanosheets (COOH-MXene) were studied using the nanosecond laser Z-scan technology. COOH-MXene showed excellent broadband OL properties with OL thresholds of 0.34 J/cm2 at 532 nm and 0.58 J/cm2 at 1064 nm, and the OL mechanism was mainly attributed to the reverse saturable absorption effect. Femtosecond time-resolved transient absorption measurements were used to clarify the ultrafast carrier dynamics in the OL process, and the results revealed that excited states absorption (ESA) in MXene was enhanced by introducing more carboxyl group terminations. When COOH-MXene was irradiated by laser pulses, excited electrons in the conduction band of MXene could transfer to the carboxyl groups and induce the ESA in the surface functional groups, resulting in the excellent OL property of COOH-MXene. [ABSTRACT FROM AUTHOR]

Two-dimensional molybdenum disulfide (MoS2) has been proved to be a good candidate in photodetectors, and MoS2/graphene (MoS2/G) heterostructure has been widely used to expand the optical response wavelength of MoS2. To clarify the carrier transfer dynamics in the MoS2/G heterostructure, time-resolved transient absorption and two-color pump–probe measurements are performed. By comparing the carrier dynamics in MoS2 and MoS2/G under different pump wavelengths, we find that interfacial excitons are formed in the heterostructure, and fast hot carriers transfer (<200 fs) from graphene to MoS2 are observed. The results indicate that the formed heterostructure with graphene can not only expand the optical response wavelength of MoS2 but also improve the response time of the device in the near-infrared region. [ABSTRACT FROM AUTHOR]

In this paper, we propose a demodulation method for refractive index (RI) sensing with tilted fiber Bragg gratings (TFBGs). It operates by monitoring the TFBG cladding mode resonance “cut-off wavelengths.” The idea of a “cut-off wavelength” and its determination method are introduced. The RI sensitivities of TFBGs are significantly enhanced in certain RI ranges by using our demodulation method. The temperature-induced cross sensitivity is eliminated. We also demonstrate a parallel-double-angle TFBG (PDTFBG), in which two individual TFBGs are inscribed in the fiber core in parallel using a femtosecond laser and a phase mask. The RI sensing range of the PDTFBG is significantly broader than that of a conventional single-angle TFBG. In addition, its RI sensitivity can reach 1023.1 nm/refractive index unit in the 1.4401–1.4570 RI range when our proposed demodulation method is used. [ABSTRACT FROM AUTHOR]

All‐inorganic lead halide perovskite nanocrystals (NCs) have been widely applied in optoelectronic devices owing to their excellent photoluminescence (PL) properties. However, poor stability upon exposure to water, UV light or heat strongly limits their practical application. Herein, CsPbBr3@Pb‐MOF composites with exceptional stability against water, UV light, and heat are synthesized by ultrasonic processing the precursors of lead‐based MOF (Pb‐MOF), oleylammonium bromide (OAmBr) and cesium oleate (Cs‐OA) solutions at room temperature. Pb‐MOF can not only provide the lead source for the in situ growth of CsPbBr3 NCs, but also the protective layer of perovskites NCs. The formed CsPbBr3@Pb‐MOF composites show a considerable PL quantum yield (PLQY) of 67.8%, and can maintain 90% of the initial PL intensity when immersed in water for 2 months. In addition, the outstanding PL stability against UV light and heat is demonstrated with CsPbBr3 NCs synthesized by the conventional method as a comparison. Finally, a green (light‐emitting diode) LED is fabricated using green‐emitting CsPbBr3@Pb‐MOF composites and exhibits excellent stability without packaging when immersed in water for 30 days. This study provides a practical approach to improve the stability in aqueous phase, which may pave the way for future applications for various optoelectronic devices. [ABSTRACT FROM AUTHOR]

The nonlinear optical response of gold nanoparticles/reduced graphene oxide (AuNPs/rGO) nanocomposites prepared by laser ablation method was studied using a femtosecond laser open-aperture (OA) Z-scan method, and an enhanced nonlinear absorption effect was observed. Using the femtosecond time-resolved pump-probe measurements, the nonlinear response mechanism in the hybrid was studied. When graphene was excited by an ultrashort laser pulse, the bleaching of valence band (VB) and the filling of conduction band (CB) took place, causing a saturable absorption (SA) effect. When decorated with gold nanoparticles, the excited carriers from the CB of graphene could transfer to the sp band of the metal before returning to the VB of graphene. This process would take place in a much longer time scale (∼50 ps) than the direct relaxation in pure graphene, causing the enhancement of the SA effect. The excited carrier dynamics were further demonstrated using femtosecond time-resolved transient absorption spectroscopy, and the interband relaxation of the excited electrons from the sp band of AuNPs to the CB of graphene was observed, resulting in the further filling of the CB of graphene and enhancement of the SA effect. [ABSTRACT FROM AUTHOR]

Single‐crystal halide perovskites are among the most promising semiconductor candidates for highly efficient optoelectronic devices due to their higher stability against moisture and light radiation and lower trap density than their polycrystalline counterparts. In this work, single‐crystal MAPbBr3 microcavities with controllable geometries and sizes are fabricated using a template‐limited method combined with an anti‐solvent diffusion growth method. The single‐crystal microcavities emit lasers around 550 nm under femtosecond laser excitation, with a lasing threshold of ≈35 µJ cm−2 and a quality factor of 1135, as well as excellent long‐term operation stability. The temporal‐spatial evolution of the lasing process in an individual microcavity is achieved by the microscopic optical Kerr‐gating technique. The temporal behaviors including pulse duration and build‐up time, emission spectra shift, and lasing mode evolution as a function of pump fluence are unveiled, and the complex relationship between the light‐induced carrier dynamics and lasing properties is clarified. Spatial heterogeneous lasing dynamics are also observed in an individual microdisk, which is attributed to the non‐uniform optical losses and carrier densities driven by structural imperfections. This study can provide a fabrication strategy for perovskite on‐chip optoelectronic devices, as well as a deeper understanding of the carrier‐density‐driven lasing dynamics in microcavities. [ABSTRACT FROM AUTHOR]

The nonlinear optical limiting (OL) property of tin phthalocyanine porous organic frameworks (Sn-Pc-POFs) dispersion in the nanosecond regime was studied, which showed excellent dispersibility and stability as well as a low OL threshold. To clarify the nonlinear optical response mechanisms in the material, the energy level structure of Sn-Pc-POFs was simulated using the density functional theory calculation, and the photoinduced carrier dynamics was studied using femtosecond time-resolved transient absorption spectroscopy. The results indicated that the large absorption cross section and long lifetime of the excited state were responsible for the excellent OL property of the material. [ABSTRACT FROM AUTHOR]

Transient energy transfer effect might occur in femtosecond pump-probe optical Kerr gate (OKG) measurements. Using time- and frequency-resolved two-dimensional pump-probe imaging spectroscopy, we are able to obtain the OKG spectra as a function of the delay time between pump and probe pulses. By analyzing the pump power dependence of the OKG spectra at different delay time, we find that due to the effect of transient energy transfer, the short-wavelength components of the OKG spectra are enhanced when the delay of the probe to pump pulse is positive, while the long-wavelength components increase when the delay is negative. [ABSTRACT FROM AUTHOR]

Carbon nanodots (C-dots) are promising substitutes for the present fluorescent nanomaterials of various applications due to their unique combination properties of intense photoluminescence (PL), low toxicity, and high aqueous solubility. However, the origin of the fascinating PL in C-dots is still a matter of current debate. Due to their complex and uncontrollable structures, the contributions of surface chemicals and carbogenic-core to their PL are poorly understood. Here, a facile two-step method combining laser ablation and UV light irradiation has been developed, in which non-fluorescent C-dots are prepared by ablating graphite powders in water using nanosecond laser, and the PL intensities are enhanced by UV light irradiation in oxygen atmosphere. Using this strategy, we are able to control the size and the surface functional groups of C-dots independently. By detailed characterization and comparison of different C-dots, we find that the intense PL in C-dots is originated from abundant surface functional groups on its surface rather than its carbogenic-core. One kind of surface functional group forms a single surface state energy level and becomes an isolated emission center with specific carrier dynamics on the surface site of C-dots. The energy gap of each surface state exhibits carbogenic-core size independent and is characterized by distinct central energies, such as C O group at 335 nm, and C O group at 430 nm. [ABSTRACT FROM AUTHOR]

Feedback-based wavefront shaping for focusing light through scattering media is an established method. In conventional feedback-based wavefront shaping, the incident light is divided into N input modes that are modulated by a spatial light modulator (SLM) using N segments, each of which has the same number and size of pixels. Here we propose light intensity-dependent feedback-based wavefront shaping using a genetic algorithm to achieve the desired wavefront shaping in less time and with fewer iterations than the conventional method. In our method, a phase mask is divided into several regions, each being allocated different phase modulation units according to the distribution of light intensity, with the pixels of the SLM being grouped non-uniformly to modulate the incident light. Compared with the conventional method, the experimental response time of our method using four subregions decreased by 15.6% and the enhancement factor increased by 30.4%. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) periodic structures were fabricated on silicon surfaces by femtosecond laser irradiation in air and water, with the assistance of a microlens array (MLA) placed in the beam's path. By scanning the laser beam along the silicon surface, multiple grooves were simultaneously fabricated in parallel along with smaller laser-induced ripples. The 2D periodic structures contained long-periodic grooves and perpendicular short-periodic laser-induced ripples, which had periods of several microns and several hundred nanometers, respectively. We investigated the influence of laser power and scanning velocity on the morphological evolution of the 2D periodic structures in air and water. Large-area grid-like structures with ripples were fabricated by successively scanning once along each direction of the silicon's surface, which showed enhanced optical absorption. Hydrofluoric acid was then used to remove any oxygen and laser-induced defects for all-silicon structures. [ABSTRACT FROM AUTHOR]

Since their discovery, carbon nanodots (C-dots) have attracted great interest due to their strong photoluminescence (PL). Yet a full understanding of the mechanisms for PL from C-dots is still under debate. In this work, we analyzed the evolution of the time-resolved PL spectra of C-dots using picosecond time-resolved spectroscopy to explore the carrier dynamics in C-dots. Our results suggest two different pathways of electron–hole radiative recombination, each with distinct relaxation time scales: a relaxation of carriers from carbogenic core onto the surface states with a slow decay (>14 ns) and direct radiative recombination of carriers on the surface states with a fast decay (∼1.3 ns). The slow decay at short-wavelength emissions is dominant due to the effective relaxation from the carbogenic core onto the surface states, while the fast decay is dominant at long-wavelength emissions. An explanation for the excitation-dependent and independent PL properties of C-dots is also presented here using this carrier dynamic model. [ABSTRACT FROM AUTHOR]

We demonstrated the time-gated ballistic imaging technique using a femtosecond optical Kerr gate (OKG) of bismuth–plumbum oxide glass, the nonlinear optical properties of which were also investigated. The third-order nonlinear refractive-indexn2of the bismuth–plumbum oxide glass was measured to be 2.19?×?10?15?cm2/W, and the nonlinear response time was estimated to be shorter than 180?fs. For the time-gated ballistic imaging, the maximum measurable optical density of turbid media using the OKG of bismuth–plumbum oxide glass was 9.3, while only 7.0 for the OKG of quartz glass. And the intensities of the images for the bismuth–plumbum oxide glass were approximately two orders of magnitude higher than that for the quartz glass. The experimental results indicated that the bismuth–plumbum oxide glass was an excellent optical material for nonlinear optical applications. [ABSTRACT FROM AUTHOR]

A femtosecond pulse laser was used to fabricate carbon nanodots (CDs), of which the particle size and photoluminescence (PL) properties could be effectively controlled by adjusting ambient pressure. By increasing the reaction pressure, the particle size of CDs gradually decreased and finally reached less than 1 nm at 4 MPa. Simultaneously, the fluorescence intensity of the CDs first increased and then decreased by further increasing the pressure. By examining the PL dynamics and the chemical structure of the CDs, we found that the PL change of products was attributed to the quantity change of functional groups attached to the CDs due to the surface area change of the carbonic core. [ABSTRACT FROM AUTHOR]

The electromagnetic induced transparency (EIT) effect originates from the destructive interference in an atomic system, which contributes to the transparency window in its response spectrum. The implementation of EIT requires highly demanding laboratory conditions, which greatly limits its acceptance and application. In this paper, an improved harmonic spring oscillation (HSO) model with four oscillators is proposed as a classical analog for the tunable triple-band EIT effect. A more general HSO model including more oscillators is also given, and the analyses of the power absorption in the HSO model conclude a formula, which is more innovative and useful for the study of the multiple-band EIT effect. To further inspect the analogizing ability of the HSO model, a hybrid unit cell containing an electric dipole and toroidal dipoles in the metamaterials is proposed. The highly comparable transmission spectra based on the HSO model and metamaterials indicate the validity of the classical analog in illustrating the formation process of the multiple-band EIT effect in metamaterials. Hence, the HSO model, as a classical analog, is a valid and powerful theoretical tool that can mimic the multiple-band EIT effect in metamaterials. [ABSTRACT FROM AUTHOR]

In order to diagnose the high-speed compressible turbulent flow field, a two-dimensional (2-D) multi-parameters measurement method based on multi-beam interferometric Rayleigh scattering (IRS) technique was proposed. Under the beam splitting of etalon, the Rayleigh scattering signals generated by the interaction between multi-beam laser probes and the flow field gas molecules formed 2-D interference measurement lattice. Each measurement point contained the thermodynamic and velocity information of the flow field corresponding to a specific spatial location. By calibrating the effective finesse and transmittance of the etalon at different incident angles, the measurement accuracy of temperature and density of high-order interferometric points was improved. A 2-D IRS measurement system was established by combining multi-beam laser probes, amplification imaging system and solid quartz etalon. A high speed jet was used to verify the technology. The distributions of temperature, density and velocity at different positions along the radial direction and axial direction of the nozzle were obtained. The results shown that the technique could be used to simultaneously measure the 2-D multi-parameter information of the flow field. [ABSTRACT FROM AUTHOR]

Germanium diselenide (GeSe2) has recently emerged as a promising material for high‐performance optoelectronic devices due to its high absorption coefficient, wide direct bandgap, and anisotropic electronic properties. For the future applications, it is necessary to understand the dynamic evolution of carriers with ultrafast response. In this work, the transient absorption spectroscopy measurements are performed to study the anisotropic dynamic evolution of GeSe2 under the polarized photoexcitation. It is find that the dynamics exhibit linear dichroism and show a significant Auger recombination process when the photoexcitation is perpendicular to the b‐axis of GeSe2. Using first‐principle and transition dipole moment calculations, it is confirmed that the more carrier localization at Γ point along the Γ‐X (perpendicular to the b‐axis) and increase the Auger recombination. In addition, the Auger recombination coefficient ≈ 1.1×10−31 cm6 s−1 is determined and demonstrated that the defect‐assisted indirect Auger recombination plays a key role in the carrier relaxation process. Through time‐resolved transient absorption spectra, it is further revealed that the ultrafast dynamical evolution of excited state absorption peaks under polarized photoexcitation. These results have implications for improving the quantum efficiency of high‐field polarization‐sensitive optoelectronics. [ABSTRACT FROM AUTHOR]

We demonstrate an environmentally stable femtosecond laser for industrial application based on all polarization‐maintaining Yb‐doped laser and experimentally explore the effect of the net cavity dispersion (NCD) on output characteristics. The oscillator emits pulses with 5.1 ps and a 23 nm spectral bandwidth, then the pulse is compressed to 88 fs. The instabilities over 120 h gives 0.32% relative root mean square noise, indicating high stability of the pulse laser. With effective regulation of NCD, we obtained the maximum spectral bandwidth of 27 nm. Such broadband oscillator with compact all‐fiber configurations provide extremely high stability should be very attractive for long‐term industrial application. [ABSTRACT FROM AUTHOR]

Controlled sequential crystallization of donors and acceptors is a critical factor for achieving enhanced phase separation and efficient charge transfer performance in polymer solar cells (PSCs). In this study, a comprehensive investigation of a structurally simple solvent additive, 1‐fluoro‐2‐iodobenzene (OFIB) is conducted, which efficiently controls the morphology of the active layer, resulting in fibrous assembly and significantly enhancing the power conversion efficiency from 16.34% to 18.38% based on the PM6:L8‐BO system. Density functional theory, molecular dynamics simulations, and grazing incidence small‐ and wide‐angle X‐ray scattering techniques reveal that the addition of OFIB to the processed blend aligns the orientation of the acceptor molecules, thereby enhancing the overall π–π stacking in the active layer. OFIB establishes nearly equal‐strength π–π interactions with the conjugated frameworks of both the donor and acceptor materials, benefiting from the multiple electron conjugation between its iodine atom and the conjugated framework in the active layer. Femtosecond‐timescale photophysical studies demonstrate that the OFIB‐optimized active layer shows reduced exciton losses at the donor–acceptor interface. This study offers a new perspective on the mechanism underlying the function of solvent additives and presents a comprehensive research methodology that will guide the development of next‐generation non‐fullerene acceptors for efficient PSCs. [ABSTRACT FROM AUTHOR]

With the wide application of intense lasers, the protection of human eyes and detectors from laser damage is becoming more and more strict. In this paper, we study the nonlinear optical limiting (OL) properties of porous carbon with a super large specific surface area (2.9 × 103 m2/g) using the nanosecond Z-scan technique. Compared to the traditional OL material C60, the porous carbon material shows an excellent broadband limiting effect, and the limiting thresholds correspond to 0.11 J/cm2 for 532 nm and 0.25 J/cm2 for 1064 nm pulses, respectively. The nonlinear scattering experiments showed that the OL behavior was mainly attributed to the nonlinear scattering effect, which is caused by the rapid growth and expansion of bubbles in the dispersion induced by laser irradiation, and the scattered light distribution is consistent with the results of Mie's scattering. These results suggest that porous carbon materials are expected to be applied to the field of laser protection in the future to further protect the human eye and precision optical instruments. [ABSTRACT FROM AUTHOR]

The advancement of carbon‐based electronics is reliant on the development of semiconducting carbon nanotubes with high purity and yield. We developed a new extraction strategy to efficiently sort SWCNTs with superior yields and purity. The approach uses two polymers, poly[N‐(1‐octylnonyl)‐9H‐carbazol‐2,7‐diyl](PCz) and poly(9,9‐n‐dihexyl‐2,7‐fluorene‐alt‐9‐phenyl‐3,6‐carbazole)(PDFP), and two sonication processes to eliminate surface polymer contamination. PCz selectively wraps large‐diameter s‐SWCNTs, with PDFP added as an enhancing molecule to increase sorting efficiency at 4‐fold compared to the efficiency of only PCz alone sorting. The purity of the sorted s‐SWCNTs was confirmed to be above 99 % using absorption and Raman spectra. Field‐effect transistors and photodetectors made from the sorted s‐SWCNTs exhibited excellent semiconductor properties and broad‐spectrum detection, with good long‐term stability. Furthermore, a photodetector using large‐tube diameter s‐SWCNTs achieved broad‐spectrum detection, which the photoresponsivity is 0.35 mA/W and the detectivity is 4.7×106 Jones. The s‐SWCNTs/graphene heterojunction photodetector achieved a photoresponsivity of 3 mA/W and a detectivity of 6.3×106 Jones. This new strategy provides a promising approach to obtain high‐purity and high‐yield s‐SWCNTs for carbon‐based photodetectors. [ABSTRACT FROM AUTHOR]

Recently, molybdenum disulfide (MoS 2) nanosheets have been used in passively mode-locked laser due to excellent saturable absorption (SA) property. To enhance their optical nonlinearity, some heterostructures such as MoS 2 /Graphene (MoS 2 /G) have been designed, but the carrier dynamics in the materials have rarely been reported. Here, the nonlinear response of MoS 2 and MoS 2 /G heterostructures nanosheets with different thickness are studied via nanosecond laser Z-scan and femtosecond time-resolved transient absorption (TA) technique. The results reveal that the ground state bleaching take place under intense laser excitation, which would block the further absorption of incident light, causing a strong SA effect of the materials. With increasing the thickness of MoS 2 , electron diffusion take place between adjacent layers, resulting in a slow recombination of excited carriers and the enhancement of SA effect in MoS 2. In MoS 2 /G, excited electrons could transfer from MoS 2 to graphene and the interlayer carrier diffusion in MoS 2 could be enhanced, prolonging the decay time of ground state bleaching effect. The slower carrier relaxation time in MoS 2 would lead a stronger SA effect for nanosecond laser pulse. This work could provide an effective strategy for designing saturable absorbers in mode-locked lasers using MoS 2 heterostructures. Image 1 [ABSTRACT FROM AUTHOR]

We demonstrated a linear-cavity fiber laser using a fiber Bragg grating (FBG) fabricated by femtosecond laser and a Sagnac loop as cavity mirrors. The temperature sensing response of the fiber laser was characterized by placing the FBG in a high-temperature environment. The stability of the fiber laser at high temperature was improved after the FBG was annealed at 1100 °C. The fiber laser can work stably as a temperature sensor at 1000 °C and its temperature sensing sensitivity is approximately 15.9 pm/°C from 300 °C to 1000 °C. • A fiber laser based on an FBG fabricated by femtosecond laser and a Sagnac loop as cavity mirrors is demonstrated. • The fiber laser can work stably as a temperature sensor at 1000 °C after the FBG was annealed at 1100 °C. • The wavelength of the fiber laser had a quadratic dependence on temperature from room temperature to 1000 °C. • The temperature–wavelength had a good linear relationship from 300 °C to 1000 °C. Its sensing sensitivity was about 15.9 pm/°C. [ABSTRACT FROM AUTHOR]

The feedback-based wavefront shaping method can be used to focus light behind or inside strongly scattering media. In this study, we investigated several characteristics of the focus after optimization to evaluate the enhancement effect of the wavefront shaping method, including the spot size, the intensity, and two types of enhancement factor. In addition, we studied the influences of various experimental parameters on these characteristics, including the number of controlled segments N, diameter of the irradiated area at the front of the scattering medium D, and distance between the expected focusing spot and scattering medium Z. A larger N and smaller Z provided a smaller focus spot. For a brighter focus spot, a larger N and smaller D and Z were required, while for a high-resolution focus spot, larger N, D, and Z were required. [ABSTRACT FROM AUTHOR]

Gold nanorod (GNR) and reduced graphene oxide (rGO) hybrids are synthesized using photochemical method based on femtosecond laser ablation without the usage of strong chemical reducing agents. The products are characterized by absorption spectra, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The formed GNR are well located on the surface of rGO sheets. By adjusting the laser ablation time, the aspect ratio and optical properties of GNR can be well controlled. The produced nanocomposites exhibited an excellent near-infrared (NIR) photothermal performance with a photothermal conversion efficiency of 77.8%, suggesting that the hybrids have large potential as agents in photothermal therapy. • Gold nanorod and graphene hybrids are synthesized using femtosecond laser. • The aspect ratio of gold nanorod can be well controlled by adjusting laser ablation time. • The produced hybrids exhibited an excellent photothermal performance at 808 nm. [ABSTRACT FROM AUTHOR]

Lead halide perovskites (LHPs) have excellent semiconductor properties. They have been used in many applications such as solar cells. Recently, the hot carrier dynamics in this type of material have received much attention as they are useful for enhancing the performance of optoelectrical devices fabricated from it. Here, we study the ultrafast hot carrier dynamics of a single CsPbBr3 microplate using femtosecond Kerr-gated wide-field fluorescence spectroscopy. The transient photoluminescence spectra have been measured under a variety of excitation fluences. The temporal evolution of bandgap renormalization and the competition between hot carrier cooling and the recovery of the renormalized bandgap are clearly revealed. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) nanoparticles (NPs) are synthesized by one-step femtosecond laser ablation of zinc powders in n-methyl pyrrolidone (NMP) at room temperature. The as-prepared ZnO NPs are fairly stable, water-soluble and have abundant surface functional groups resulting in a strong fluorescence in the visible region. By further annealing the ZnO NPs in the reacting solvent up to 120∘C, the photoluminescence (PL) intensity of material can be significantly enhanced. Besides, the PL of ZnO NPs can change from blue to green by controlling the annealing temperature. The products exhibit excellent temperature sensing with high temperature sensitivity and a 1.3% change per ∘C response over a linear temperature sensing range (6–84 ∘ C) in aqueous buffer, which matches well with the physiologically relevant temperatures. Hence, the ZnO nanoparticle system can serve as a promising candidate for practical fluorescent temperatures nanosensors which can be used for accurate temperature monitoring within biological systems. Water-soluble and photoluminescent ZnO NPs are synthesized by femtosecond laser ablation of zinc powders at room temperature. By further annealing, the photoluminescence intensity of the products can be significantly enhanced. The ZnO NPs exhibit excellent temperature sensing with a high sensitivity of 1.3% change per ∘C over a linear range of 6–84∘C in aqueous buffer, which can serve as a promising candidate for fluorescent temperature nanosensors to be used for accurate temperature monitoring within biological systems. [ABSTRACT FROM AUTHOR]

All-inorganic lead halide perovskites nanocrystals (NCs) have been demonstrated to be promising candidates for optoelectronic devices, but preparing perovskite NCs with high photoluminescence quantum yields (PLQYs) and excellent stability has been a challenge. In this work, CsPbBr 3 /Cs 4 PbBr 6 core/shell NCs with a PLQYs of 87.23% and long-term stability in ambient environments was prepared by room temperature inverse microemulsion method. The excellent stability of the sample was attributed to the protection of Cs 4 PbBr 6 , and higher PLQYs could be owing to the passivation effect of the core/shell structure. To illustrate the distribution of photogenerated carrier in the core/shell structure, a confined excitons model was proposed based on time-resolved PL and temperature dependent PL measurements. Femtosecond time-resolved transient absorption spectra measurements were performed upon different excitation wavelength to unveil the photogenerated carrier dynamics in core/shell NCs. Upon 300 nm excitation, a carrier transfer process with the time of 3.18 ps from shell to core layer was observed. Furthermore, both two- and three-photon absorption PL was discovered in core/shell NCs, further verifying the carrier transfer process. [Display omitted] • Fabrication of strongly luminescent and highly stable CsPbBr 3 /Cs 4 PbBr 6 core/shell NCs. • A confined excitons model proposed for illustrating the higher PLQY in core/shell NCs. • A carrier transfer process from shell to core layer was observed in core/shell NCs. • Multi-photon absorption PL was observed further verifying the carrier transfer process. [ABSTRACT FROM AUTHOR]

Argon dielectric barrier discharge driven by the dual frequency at atmospheric pressure has been investigated by a 1D fluid model. Temporal evolutions of voltage and charge density on dielectric surface, fluxes of electrons and ions on the surface, the spatiotemporal distribution of electron generation rate, and the spatial distribution of electron density are studied with various low-frequency (LF) voltages. Minimum sustained discharge amplitude of high frequency (HF) voltage and spatiotemporal mean electron density over one LF period varying with sheath voltage (α → γ) are also discussed. Results show that in α mode, the electron flux on the dielectric surface decreases significantly when the LF voltage amplitude is lower while the ion flux is less affected. The positive charge density on the surface increases, causing the surface voltage waveform to shift upward. When the LF voltage amplitude is 40 V and that of HF voltage is 87 V, the positive and negative values of voltage amplitude of dielectric surface are 182 and 32 V. As the LF voltage amplitude increases further, the sheath formation time is significantly delayed and the discharge terminates, and the rate of electron generation decreases significantly. The discharge is extinguished when the amplitude of LF voltage is 68 V while it regains when the amplitude reaches up to 750 V. In γ mode, when the amplitude of HF voltage reaches or exceeds its minimum sustained discharge value, the generation and distribution of electrons are almost unaffected by the amplitude of LF voltage. [ABSTRACT FROM AUTHOR]

Microchannel plates (MCPs) are widely utilized as key device components in various photomultipliers; however, the performance of MCPs cannot be further improved by traditional processing. Atomic layer deposition (ALD) is a promising route to prepare a composite conductive layer and secondary electron emission (SEE) layer structure on the inner wall of the MCP. Moreover, ZnO is an essential component of a composite conductive layer, which is located at the bottom of the SEE layer and significantly influences the SEE coefficient, which, in turn, affects the gain performance of MCPs. Herein, ALD is used to deposit different thicknesses of ZnO films (1–50 nm) on an Si substrate, resulting in an ZnO/Si double-layer film structure. The relationship between the SEE coefficient and the primary electron energy of ZnO films with different thicknesses was established. The maximum secondary electron yield value of 2.04 is achieved at a film thickness of 30 nm. Moreover, Dionne's SEE model and theory of semiconductors are used to simulate and verify the experimental results. These results provide useful guidelines for the development of ALD-MCPs. [ABSTRACT FROM AUTHOR]

The separation of highly pure single-chirality single-walled carbon nanotubes (SWCNTs) is challenging and also in demand due to their intrinsic physical, optical, and electronic properties. The use of single-chirality and their performance characteristics makes them a selective candidate for multifunctional applications and opens a new front in nanotube development. It has previously been reported that SWCNTs can be separated in various ways by employing direct control and post-synthesis approaches. Herein, we review the separation of single-chiralities of SWCNTs on account of simplicity and time/cost effectiveness by using gel chromatography. The most recent progress in the controlled synthesis of SWCNTs is comprehensively reviewed in terms of selective-diameter, single-chirality, and specific geometric shape. The method to achieve the single-chirality of SWCNTs is also highlighted. Besides addressing COVID-19 characteristics, epidemiology, and pathology, we also review the most recent developments in nano-biosensors for the rapid and early detection of COVID-19. Furthermore, the photothermal/bioimaging response of single-chirality is reviewed in order to enhance the cytotoxicity of drugs against cancer cells over simple carbon nanotubes (CNTs). The single-chirality allows for precise imaging (due to efficient absorption and emission) of tumors/blood vessels up to ∼10-fold higher by injecting a low dose. We hope this review stimulates further study on single-chirality controlled SWCNTs for practical applications. [ABSTRACT FROM AUTHOR]

The excellent performance of InP/ZnSe/ZnS core/shell/shell quantum dots (CSS-QDs) in light-emitting diodes benefits from the introduction of a ZnSe midshell. Understanding the changes of ultrafast carrier dynamics caused by the ZnSe midshell is important for their optoelectronic applications. Herein, we have compared the ultrafast carrier dynamics in CSS-QDs and InP/ZnS core/shell QDs (CS-QDs) using femtosecond transient absorption spectroscopy. The results show that the ZnSe midshell intensifies the electron delocalization and prolongs the in-band relaxation time of electrons from 238 fs to 350 fs, and that of holes from hundreds of femtoseconds to 1.6 ps. We also found that the trapping time caused by deep defects increased from 25.6 ps to 76 ps, and there were significantly reduced defect emissions in CSS-QDs. Moreover, the ZnSe midshell leads to a significantly increased density of higher-energy hole states above the valence band-edge, which may reduce the probability of Auger recombination caused by the positive trion. This work enhances our understanding of the excellent performance of the CSS-QDs applied to light-emitting diodes, and is likely to be helpful for the further optimization and design of optoelectronic devices based on the CSS-QDs. [ABSTRACT FROM AUTHOR]

The influence of the size parameter of the scatterers on ultrafast optical Kerr gate (OKG) imaging is investigated in highly scattering poly-disperse turbid media. The results show that in a poly-disperse turbid medium, which in our case, is a suspension of two different sized mono-disperse microspheres, the temporal and spatial behaviors of the light pulses transmitted through it are dominated by the smaller microspheres. The contrasts of the OKG images for the poly-disperse microsphere sample are closer to the contrasts of the OKG images for the smaller sized mono-disperse microsphere sample. [ABSTRACT FROM PUBLISHER]

Two-mode interference effects in slot waveguides have been predicted and investigated through plane wave expansion and finite-difference time-domain methods. A broadband 1×2 power splitter (PS) based on this effect is presented, and its transmission characteristics are investigated by using finite-difference time-domain method. Calculated results indicate that, for the 1×2 PS whose interaction length is as short as 0.509 µm, the high transmission (≥95%) is observed within a wavelength range of 1.389–1.747 µm, corresponding to a relative bandwidth of 22.87%. Combining three 1×2 PS, we construct a 1×4 PS with excellent transmission characteristics. Those simple PS are expected to be applied to highly dense photonic integrated circuits. [ABSTRACT FROM AUTHOR]

A compact plasmonic structure is proposed to actualize the subwavelength beam focusing, through a metal slit array arranged along a triangular or trapezium surface profile. The incident light passes through the metal slits in the form of surface plasmon polaritons (SPPs) and then scattered into radiation fields. The constructive interference of radiation fields from individual slits with different depths and widths gives rise to beam focusing. The advantages of the proposed plasmonic lens are having a much smaller lateral dimension and broad working wavelength range. This is of importance for realizing densely integrated photonic circuits. The finite-difference time-domain (FDTD) method is employed to verify the proposed design. The simulation results indicate that the focal spot is beyond the diffraction limit. [ABSTRACT FROM AUTHOR]

We study the optical limiting (OL) property of a newly emerged MXene material, niobium carbide (Nb2CTx) nanosheets, using nanosecond laser Z-scan measurement. The nanosheets exhibited excellent OL property, and the OL thresholds are estimated to be about 0.35 and 0.44 J / cm2 for 532 and 1064 nm, respectively. Compared with the traditional OL material, reduced graphene oxide, Nb2CTx nanosheets show a better OL property. The nonlinear scattering (NLS) measurements indicate that the excellent OL behavior of the nanosheets originates mainly from the strong NLS effect due to the good photothermal property of the material. [ABSTRACT FROM AUTHOR]

A comparative analysis of sorted semiconducting (sc‐) single‐walled carbon nanotubes (SWCNTs) films, metallic (m‐) SWCNTs films, pristine SWCNTs films, and graphene‐based simple two‐terminal sensors for the applications of ammonia gas sensing is presented. The comparison of the sensing response of different devices by separately measuring the SWCNTs film resistance and the contact resistance between SWCNTs and the electrodes reveals that the performance mainly relies on the modification of tube conductivity under exposure to gas. Moreover, the measurements show that the highest sensitivity of the devices is achieved by use of sc‐SWCNTs as the conducting channels. Sensor coated with surfactant‐free sc‐SWCNTs shows a sensitivity of 0.78% ppm at 5–100 ppm ammonia (NH3) concentrations that happened to be ≈28, ≈22, and ≈173 times more sensitive than pristine‐SWCNTs, m‐SWCNTs, and graphene‐based sensors, respectively, at 50 ppm and ≈4.5 times the previously reported sc‐SWCNTs‐based sensor at 5 ppm. Notably, all the experiments values are achieved at room temperature without any extra heating treatment for the recovery process. These results show that surfactant‐free sc‐SWCNTs provide a promising way of creating sensors with improved selectivity and sensitivity, which predicts the auspicious prospects in the development of future applications. [ABSTRACT FROM AUTHOR]

• A theoretical model of optical Kerr gate with a double gate pulses (D-OKG) was proposed. • The dependence of the D-OKG performance on the relative intensity and the relative delay time of the two gate pulses was investigated with our theoretical model. We demonstrated an improved optical Kerr gate with double gate pulses (D-OKG) to realize an ultrashort switching time even with a slow-response optical Kerr medium. A theoretical model of D-OKG was established and the dependence of the D-OKG performance on the relative intensity and the relative delay time of the two gate pulses was investigated. An integrated optimal condition was predicted. The D-OKG was experimentally built and optimized according to the simulation. The dependence of the D-OKG performance on the two gate pulses was confirmed. In our experiment, the achieved values for transmittance and switching time were 45 % and 150 fs, respectively. Compared to the conventional OKG, the D-OKG owns an integrated optimal performance in the femtosecond regime, and has the potential for a wide range of ultrafast optical switch applications. [ABSTRACT FROM AUTHOR]

We studied the structural and elemental evolutions during the femtosecond laser percussion drilling of high-aspect-ratio diamond microholes. Microholes 225-μm-deep having an aspect ratio of 15 were drilled with an exposure time of 100 s and a laser power of 60 mW. It is found that when the specimen was machined by femtosecond laser at low power and short exposure time, the laser-affected zone (LAZ) may be still solid in the interior rather being void, even it reached the bottom of the diamond. A clear crack appeared between the solid portion and pristine diamond. Elemental analysis revealed that oxygen was incorporated into the solid portion of the LAZs, and its atomic percentage reached 6.5% for a laser power of 10 mW at initial position and decreased as the depth increased in the solid portion. The wall of the void contained nearly no oxygen. Furthermore, nanoripples were observed on the sidewall surface of the hole. [ABSTRACT FROM AUTHOR]

Asymmetric molecule strategy is considered an effective method to achieve high power conversion efficiency (PCE) of polymer solar cells (PSCs). In this paper, nine oligomers are designed by combining three new electron-deficient units (unitA)—n1, n2, and n3—and three electron-donating units (unitD)—D, E, and F—with their π-conjugation area extended. The relationships between symmetric/asymmetric molecule structure and the performance of the oligomers are investigated using the density functional theory (DFT) and time-dependent density functional theory (TD–DFT) calculations. The results indicate that asymmetry molecule PEn2 has the minimum dihedral angle in the angle between two planes of unitD and unitA among all the molecules, which exhibited the advantages of asymmetric structures in molecular stacking. The relationship of the values of ionization potentials (IP) and electron affinities (EA) along with the unitD/unitA π-extend are revealed. The calculated reorganization energy results also demonstrate that the asymmetric molecules PDn2 and PEn2 could better charge the extraction of the PSCs than other molecules for their lower reorganization energy of 0.180 eV and 0.181 eV, respectively. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) are biophilic quantum dots with excellent luminescent properties, however, the aggregation-caused quenching (ACQ) effect is a serious limitation for their application in solid-state devices. In this manuscript, a solid-state luminescent blue CDs (B-CDs) with a high fluorescence quantum yield of 52% was prepared by a microwave-assisted method. The B-CDs showed weak fluorescence and with a photoluminescence fluorescence quantum yield (PLQY) of only 0.63% in aqueous solution, but exhibited an aggregation-induced emission in the solid state. The AIE phenomenon of B-CDs was shown to result from the inhibition of surface chromophore motion during aggregation by characterizing the PL intensity under different ratios of DCM (poor solvent). Furthermore, the fluorescence kinetic mechanism associated with the B-CDs was investigated by the time-resolved PL. Finally, a blue LED with CIE coordinates of (0.15, 18) was fabricated using B-CDs as the phosphor, showing a promising potential application in solid-state optoelectronic devices. • Green and safe fabrication of CDs with efficient solid-state blue light emission. • A discovery and demonstration of CDs' aggregation-induced emission effect. • A carrier kinetic model abort CDs' AIE effect was proposed based on time-resolved PL. [ABSTRACT FROM AUTHOR]

A compact 51.6-W, 26- μ J all-fiber integrated Yb-doped femtosecond laser source with pulse durations of 692 fs despite ∼ 18 π nonlinear phase shift accumulation in the main amplifier is demonstrated by using fiber quasi-rectangular pulse pre-shaping. The numerical results are in good agreement with the experiment. Due to the advantages of an all-fiber spliced structure and a minimal pulse stretching ratio (from 26.3 ps to ∼ 70 ps), just a small size of gratings and a short separation distance between the two gratings in the compressor is required. Therefore, the laser source is exceedingly compact, robust, cost-effective, and easy to assemble. This technique is anticipated to accelerate the use of fiber femtosecond lasers in industrial applications. • All-fiber spliced structure with ∼ 18 π nonlinear phase shift in the main amplifier. • High peak power and density as much as 0.4 MW and 80 GW/cm 2 respectively in the main amplifier • Compact structure with small compressor makes the laser robust, reliable, and cost-effective. • Near-diffraction-limit beam quality suitable for micro-machining and related applications. [ABSTRACT FROM AUTHOR]

For most cancers, multimodal cancer synergistic therapy is far more effective than monotherapy. Herein, a multifunctional nanocarrier based on lentinan (LTN) in situ functionalized molybdenum disulfide nanoflowers (MoS2@LTN NFs) is developed by a simple hydrothermal method together with the in situ surface modification strategy. We utilized them to load chemotherapeutic drug gemcitabine (GEM) for in vitro and in vivo chemo-photothermal (Chemo-PTT) therapy. The results show that MoS2@LTN NFs have the following characteristics: (1) the in situ encapsulated LTN can affect the crystal structure of MoS2, and the light absorption capacity of MoS2@LTN is 1.26 times higher than that of pure MoS2; (2) it could achieve different drug release behaviors by dual stimulation with acidic pH and NIR laser irradiation; (3) in vivo experiments demonstrated that synergistic Chemo-PTT therapy achieved by using MoS2@LTN-GEM has a more favorable therapeutic effect than monotherapy. Accordingly, MoS2@LTN NFs could be developed as promising nanocarriers for synergistic therapy. [ABSTRACT FROM AUTHOR]

We demonstrate the control of femtosecond single-filament formation via feedback-based wavefront shaping. It is observed that the optimal phase profile forms a single-filament with closed-loop genetic algorithm. Using this method, the position stability of the filament can be significantly improved, and the position of the single filament can be flexibly adjusted. Additionally, a two-step approach combining the premodulation of pinhole with wavefront shaping is presented for forming a bright single filament rapidly. • Succeeded in getting a stable and bright single filament. • Optimization processes from multiple filaments to single filament are displayed. • A two-step strategy is an effective technique to fast control single filament. [ABSTRACT FROM AUTHOR]

Phthalocyanines with an 18 π-electron conjugated structure have intrinsic nonlinear optical response, but their agglomeration in solution and films is a bottleneck toward their optical limiting device processing. Herein, we develop three sp3-hybridized carbon bridge polyphthalocyanine porous organic frameworks (Pc-POFs) with an enhanced nonlinear absorption effect and optical limiting properties. The strong covalent bond linked porous structures in Pc-POFs could improve their optical limiting properties by inhibiting the relaxation of the molecule and increasing their excited state absorption. Moreover, the Sn-Pc-POF which introduces a Sn metal ion in the phthalocyanine center, exhibited an optical limiting threshold of 0.37 J cm−2 at 532 nm nanosecond laser, which is highly competitive in comparison with the state-of-the-art 2D optical limiting materials such as graphene and layered transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

Carbon nanodots have been demonstrated to be an effective reducing agent in fabricating silver nanoparticles. In this study, the dependence of reduction efficiency of the CDs on the irradiation wavelength and their photoluminescence property is investigated. We find that the CDs excited by short wavelength light shows much higher photoreducibility than those excited by longer wavelength irradiation, although their PL intensity might be about the same. By analyzing the PL and the time-resolved PL property of the formed CDs-Ag NPs composites we find that, when the CDs are excited, there are two kinds of recombination path ways of the carriers contributing to their photoluminescence: the direct excitation of surface states, and the excited electrons from carbonic-core transferred to the surface states; only the electrons originates from the intrinsic carbonic-core excited by short wavelength can reduce the Ag ions, while those originates from the direct excitation of the surface states by long wavelength light are ineffective. The proposed reduction kinetics of Ag ions is significant to understand the photoreduction property of the CDs. • Ag NPs were prepared using CDs excited by UV light as the reductant. • The influence of irradiation wavelength on the reduction efficiency was studied. • A hypothesis was proposed to explain the reduction mechanism of silver ions. • Only electrons excited from the carbonic-core of CDs could reduce Ag ions. [ABSTRACT FROM AUTHOR]

It is a challenging and application‐oriented goal to achieve the metal/semiconductor separation of large diameter single‐walled carbon nanotubes (SWCNTs) using a dextran‐based gel chromatograph. Herein, a study of the temperature effect on the metal/semiconductor separation of plasma torch SWCNTs through dextran‐based gel chromatograph is conducted. The temperature governs the interaction between SWCNTs and hydrogel, thus enabling the sorting of SWCNTs by electronic type. In addition, the temperature effect enables the metallic (m‐) and semiconducting (sc‐) fraction to be resolved and eluted using a single cosurfactant system, so that the process can be iterated easily. The fractions containing up to 99% of sc‐SWCNTs and 95% of m‐SWCNTs have been obtained after three times of iteration. The iteration process is not only applicable to sc‐SWCNTs and m‐SWCNTs, but also practicable for the cosurfactant system and circumvents additional preparation steps. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) is utilized to prepare thin MgO coatings 1–50 nm on Si substrate. In addition, secondary electron emission (SEE) coefficient of MgO/Si double-layered structure is evaluated as a function of coating thickness and primary electron (PE) energy. After neutralizing the surface of test specimen, we have accurately analyzed the relationship between secondary electron yield (SEY) of MgO coating and PE energy. Meanwhile, SEE characteristics of MgO/Si double-layered structure have been systematically analyzed. A maximum SEY value of 6.15 has been achieved at coating thickness of 30 nm and PE energy of 550 eV. Furthermore, theoretical model is established by using Dionne's SEE model to analyze experimentally measured SEY data, demonstrating consistency between experimentally measured and theoretically calculated results. This work demonstrates that SEE level of MgO coating can be optimized by tuning coating thickness and presents novel insights into SEE characteristics of composite materials. Those results can serve as a baseline for further design and fabrication of a wide array of electronic devices. [ABSTRACT FROM AUTHOR]