Ultrafast Response and Threshold Adjustable Intelligent Thermoelectric Systems for Next‑Generation Self‑Powered Remote IoT Fire Warning

Fire warning is vital to human life,economy and ecology.However,the development of effective warning systems faces great challenges of fast response,adjustable threshold and remote detecting.Here,we propose an intelligent self-powered remote IoT fire warning system,by employing single-walled carbon nanotube/titanium carbide thermoelectric composite films.The flexible films,prepared by a convenient solution mixing,display p-type characteristic with excellent high-temperature stability,flame retardancy and TE(power factor of 239.7±15.8μW m^(-1) K^(-2))performances.The comprehensive morphology and structural analyses shed light on the underlying mechanisms.And the assembled TE devices(TEDs)exhibit fast fire warning with adjustable warning threshold voltages(1–10 mV).Excitingly,an ultrafast fire warning response time of~0.1 s at 1 mV threshold voltage is achieved,rivaling many state-of-the-art systems.Furthermore,TE fire warning systems reveal outstanding stability after 50 repeated cycles and desired durability even undergoing 180 days of air exposure.Finally,a TED-based wireless intelligent fire warning system has been developed by coupling an amplifier,analogto-digital converter and Bluetooth module.By combining TE characteristics,high-temperature stability and flame retardancy with wireless IoT signal transmission,TE-based hybrid system developed here is promising for next-generation self-powered remote IoT fire warning applications.

Two-Photon Fluorescence Properties and Ultrafast Responses of a Hyperbranched Diketo-Pyrrolo-Pyrrole Polymer with Triphenylamine as the Core

The two-photon fluorescence properties and ultrafast responses of a hyperbranched polyyne （hb-DPP-J2） with triphenylamine as the central core, Diketo-Pyrrolo-Pyrrole as the connecting unit and electron acceptor are studied. The polymer has a D-π-A-π-D conjugated structure along the extended polyyne w-bridge systems, and the effective condugated unit repeats itself in the whole hyperbranehed polymer chain. The polymer exhibits a large two-photon absorption cross section and high fluorescence quantum yields. The ultrafast dynamic results give a deep understanding of the excited energy transfer processes under excitation, and reveal a long relaxation lifetime of the intramolecular charge transfer （ICT） state.

Alloying-engineered high-performance broadband polarized Bi_(1.3)In_(0.7)Se_(3)photodetector with ultrafast response

Topological insulators have important potential for applications in the field of nano/micro-optoelectronic devices.However,the large dark current seriously hinders the improvement of device performance.Alloying is an important means to control the physical properties of topological insulators.In this work,we have designed and prepared Bi_(1.3)In_(0.7)Se_(3)crystals.The optoelectronic properties of the individual Bi_(1.3)In_(0.7)Se_(3)nanowire-based photodetector are systematically investigated.The photodetector is very sensitive to broadband wavelength from solar-blind ultraviolet C(254 nm)to near-infrared(1,064 nm),showing superior optoelectrical properties with photoresponsivity of 241.3 A·W^(–1)and detectivity of 1.18×10^(12)Jones at 638 nm.Furthermore,the photodetector demonstrates ultrafast photoresponse characteristics with a photoresponse time of about 770 ns,which is 3 to 6 orders of magnitude lower than other compound semiconductors based on Bi or In reported so far.In addition,it also exhibits good polarization sensitivity in a broadband range from ultraviolet C(266 nm)to near-infrared(1,064 nm)and obtained the maximum dichroic ratio is 1.73 at 1,064 nm.Our results suggest that this platform creates new opportunities for the development of low-cost,high-sensitivity,high-speed,and broadband angle-sensitive photodetectors.

CO_2-responsive Polymeric Fluorescent Sensor with Ultrafast Response

Response speed is one of the most important evaluation criteria for CO2 sensors. In this work, we report an ultrafast CO2 fluorescent sensor based on poly[oligo（ethylene glycol） methyl ether methacrylate]-b-poly[N,N-diethylaminoethyl methacrylate-r-4-（2- methylacryloyloxyethylamino）-7-nitro-2,1,3-benzoxadiazole] [POEGMA-b-P（DEAEMA-r-NBDMA）], in which DEAEMA units act as the CO2-responsive segment and 4-nitrobenzo-2-oxa-l,3-diazole （NBD） is the chromophore. The micelles composed of this copolymer could disassemble in 2 s upon CO2 bubbling, accompanying with enhanced fluorescence emission with bathochromic shift. Furthermore, the quantum yield of the NBD chromophore increases with both the CO2 aeration time and the NBD content. Thus we attribute the fluorescent enhancement to the inhibition of the photo-induced electron transfer between unprotonated tertiary amine groups and NBD fluorophores. The sensor is durable although it is based on ＂soft＂ materials. These micellar sensors could be facilely recycled by alternative CO2/Ar purging for at least 5 times, indicating good reversibility.

Hydrophobic ionic liquid-in-polymer composites for ultrafast,linear response and highly sensitive humidity sensing

Traditional ionic liquids are sensitive to humidity but with long response time and nonlinear response.Pure liquid-state ionic liquids are usually hard for dehydration which have ultralong response time for humidity sensing.The immobilization of ionic liquids provide a possible way for high performance humidity sensing.Hydrophobic materials and structures also promised faster response in humidity sensing,because of easier desorption of water.In this work,we prepared flexible humidity sensitive composites based on hydrophobic ionic liquid and polymer.The combination of hydrophobic ionic liquid with hydrophobic polymer realized linear response,high sensitivity with low hysteresis to humidity.By adjusting the ratio of ionic liquid,not only the impedance but also the hydrophobicity of composite could be modulated,which had a significant influence on the humidity sensing performance.The morphology and microstructure of the material also affected its interaction with water molecules.Due to the diverse processing methods of polymer,highly transparent film fabricated by spinning-coating and nanofibrous membrane fabricated by electrospinning could be prepared and exhibited different response time,which could be used for different application scenarios.Especially,the fibrous membrane made with electrospinning method showed an ultrafast response and could distinguish up to 120 Hz humidity change,due to its fibrous structure with high specific surface area.The humidity sensors with ultrafast,linear response and high sensitivity showed potential applications in human respiratory monitoring and flexible non-contact switch.To better show the multifunction of ionic liquid-polymer composite,as a proof of concept,we fabricated an integrated humidity sensitive color change device by utilizing lower ionic liquid content composite for sensing in the humidity sensing module and higher ionic liquid content composite as the electrolyte in the electrochromic module.

Ultrafast Nonlinear Optical Response of Two-dimensional MoS_(2)/Bi_(2)Te_(3) Heterostructure

Controlled stacking of different two-dimensional(2D)atomic layers hold great promise for significantly optimizing the optical properties of 2D materials and broadening their applications.Here,vertical 2DMoS_(2)/Bi_(2)Te_(3) heterostructures with high crystallinity and optical quality have been successfully constructed,through drop-casting 2D Bi_(2)Te_(3) flakes on chemical vapor deposition(CVD)-grown MoS_(2) flakes.Based on our homebuilt micro Z-scan and pump-probe measurement,we precisely investigated and compared the nonlinear optical(NLO)performance of an individual micro-sized MoS_(2) flake before and after stacking 2D Bi_(2)Te_(3) nanoplates.Moreover,layer-dependent ultrafast carrier dynamics of CVD-grown MoS_(2) flakes were also explored.Owing to the efficient charge transfer from the monolayer(1 L)MoS_(2) to 2D Bi_(2)Te_(3),the 1L MoS_(2)/Bi_(2)Te_(3) heterostructure demonstrated excellent NLO performance with superior nonlinear saturable absorption coefficient and ultrashort carrier lifetime.Our work greatly enriches our understanding of 2D heterostructure and paves the way for designing new type of tunable 2D photonics materials by combining the optical advantages of different 2D materials.

Broadband ultrafast nonlinear optical response of few-layers graphene: toward the mid-infrared regime

Gapless linear energy dispersion of graphene endows it with unique nonlinear optical properties, including broadband nonlinear absorption and giant nonlinear refractive index. Herein, we experimentally observed that fewlayers graphene has obvious nonlinear absorption and large nonlinear refraction, as investigated by the Z-scan technique in the mid-infrared（mid-IR） regime. Our study may not only, for the first time to our knowledge, verify the giant nonlinear refractive index of graphene(～10-7cm2∕W) at the mid-IR, which is 7 orders of magnitude larger than other conventional bulk materials, but also provide some new insights for graphene-based mid-IR photonics,potentially leading to the emergence of several new conceptual mid-IR optoelectronics devices.

Dependence of Quantum Yields on Size of Ag Nano-particle Embedded in BaO Thin Film

Theoretical dependence of the quantum yields on the size of Agnano-particle distribution from 0.8 nm to 37 nm embedded in BaOsemiconductor is discussed. The calculation results show that theincrease in Ag nano-particle diameter leads to the increase of thequantum yield threshold and the emergence of the rough Gaussian form,the results also shown that the greater increase in Ag nano-particlediameter causes the emergence of the exact Gaussian form and makesthe peaks rise up.