Easy-to-perform organic-solvent-free synthesis of carbon dots with strong green photoluminescence

Carbon dots(CDs)have been extensively studied owing to their fascinating optical properties and wide potential applications.Here,we report an easy-to-perform and organic-solvent-free synthesis strategy for green-emissive CDs(G-CDs)possessing high photoluminescence(PL)quantum yield(QY).The G-CDs are synthesized by heating the homogeneous precursors of citric acid and cyanamide in an open vessel,circumventing the use of organic solvents,complex operations,high-pressure reactors,and expensive instruments in the synthesis process.The effect of various reaction variables on the formation and the optical properties of G-CDs are systematically investigated.The resultant G-CDs show bright PL emission at 521 nm with PL QY up to 73%.Then a white light-emitting diode(LED)with Commission Internationable de L'Eclairage(CIE)coordinates of(0.33,0.34)and color rendering index(CRI)of 92 is constructed based on G-CDs/thermoplastic polyurethane(TPU)composite.Moreover,a visual microfluidic detection platform is designed by using G-CDs as fluorescent probes for rapid quantitative detection of Fe^(3+),Cu^(2+),and Mn^(2+)metal ions,which can realize synchronized testing of multiple samples.This study might promote the development and preparation methods of high-performance CDs with various optical applications.

The functional significance of residual yolk in lizards

Residual yolk is assumed to be an important source of energy and nutrients during early life in nonmammalian amniotes.Available data show that the mean size of residual yolk is far smaller in lizards than in turtles,snakes,crocodiles,and birds,raising a question of whether residual yolk is of functional significance in lizards.Here,we compared data from 26 lizard species with those from other nonmammalian amniotes to test the hypothesis that residual yolk is functionally less significant in species producing more fully developed offspring.In our sample,species mean offspring water contents ranged from 73%to 84%of body wet mass;species mean proportions of carcass dry mass,fat-body dry mass,and residual yolk dry mass to offspring dry mass ranged from 84%to 99%,0%to 5.0%,and 0%to 14.4%,respectively.Lizards are,on average,more fully developed at hatching or birth than snakes,as revealed by the fact that the mean proportion of carcass dry mass to body dry mass and offspring water contents were both higher in lizards than in snakes.We conclude that the functional significance of residual yolk during early life is generally less evident in lizards.Even in the lizards where residual yolk is of potential functional significance,this portion of yolk contributes little,if any,to postembryonic growth.Future work could usefully collect data across a wider spectrum of reptile taxa to establish a precocial-altricial continuum and test the hypothesis that species with a smaller amount of residual yolk are closer to the precocial end of the continuum.

In-situ synthesis of stable perovskite quantum dots in core-shell nanofibers via microfluidic electrospinning

Perovskite quantum dots(PQDs) possess remarkable optical properties, such as tunable photoluminescence(PL) emission spectra, narrow full width at half maximum(FWHM) and high PL quantum yield(QY), endowing the PQDs great application prospects. However, the inherent structural instability of PQDs has seriously hindered the application of PQDs in various photoelectric devices. In this work, a microfluidic electrospinning method was used to fabricate color-tunable fluorescent formamidinium lead halogen(FAPbX_(3), X = Cl, Br, I) PQDs/polymer core-shell nanofiber films. The core-shell spinning nanofiber not only supplies the interspace for the in-situ formation of PQDs, but also significantly reduces the permeability of moisture and oxygen in the air, which greatly improves the stability of PQDs. After adjusting the composition of precursors, the blue-emissive polystyrene(core) and polymethyl methacrylate(shell) coated FAPbCl_(3) QDs(abbreviated as PS/FAPbCl_(3)/PMMA, hereinafter), green-emissive PS/FAPbBr_(3)/PMMA and redemissive PS/FAPbI_(3)/PMMA nanofiber films were fabricated with the highest PL QY of 82.3%. Moreover,the PS/FAPbBr_(3)/PMMA nanofiber film exhibits great PL stability under blue light irradiation, long-term storage in the air and water resistance test. Finally, the green-and red-emissive nanofiber films were directly applied as light conversion films to fabricate wide-color-gamut display with the color gamut of 125%, indicating their tremendous potentials in optoelectronic applications.

Stochastic Volatility Modeling based on Doubly Truncated Cauchy Distribution and Bayesian Estimation for Chinese Stock Market

In order to measure the uncertainty of financial asset returns in the stock market, this paper presents a new model, called SV-dt C model, a stochastic volatility(SV) model assuming that the stock return has a doubly truncated Cauchy distribution, which takes into account the high peak and fat tail of the empirical distribution simultaneously. Under the Bayesian framework, a prior and posterior analysis for the parameters is made and Markov Chain Monte Carlo(MCMC) is used for computing the posterior estimates of the model parameters and forecasting in the empirical application of Shanghai Stock Exchange Composite Index(SSECI) with respect to the proposed SV-dt C model and two classic SV-N(SV model with Normal distribution)and SV-T(SV model with Student-t distribution) models. The empirical analysis shows that the proposed SV-dt C model has better performance by model checking, including independence test(Projection correlation test), Kolmogorov-Smirnov test(K-S test) and Q-Q plot. Additionally, deviance information criterion(DIC) also shows that the proposed model has a significant improvement in model fit over the others.

Facile synthesis,high fluorescence and flame retardancy of carbon dots

Facile strategy enabling the fabrication of carbon dots(CDs)with favorable performance useful for various applications is highly desirable.Here,we report the fabrication of highly fluorescent carbon dots(CDs)towards sensitive metal ion detection,brightly fluorescent printing pattern,as well as green flame retardants for synthetic polymeric materials.CDs are synthesized by solvothermal treatment of polypropylene carbonate(PPC)with ethylenediamine,and the quantum yield of CDs could increase from 30%to 86%by further adding trace of citric acid.The abundant functional groups on the surface of CDs allow CDs well incorporated into polymers to form CD-loaded polystyrene(PS)microspheres,which are employed to construct fluorescent supraballs via triphase microfluidic technique and used as“inks”for uniform fluorescent patterns.Interestingly,the resultant CDs show good flame retardancy for highly flammable polymeric foams and fibers.The CDs surpass previously reported flame-retardant additives,to show excellent combustion resistance that the addition of 20 wt%CDs causes 75%decrease in the peak of heat release rate(P-HRR)for polyurethane(PU)foams.Significantly,a molecular dynamics simulation process for PU/CDs combustion is constructed.This work may spur the preparation and application of highperformance carbon-based nanomaterials.

Carbon dots embedded nanofiber films:Large-scale fabrication and enhanced mechanical properties

Valuable application prospects and large-scale production technologies are powerful driving forces for the development of materials science.Carbon dots(CDs)are a kind of promising carbon-based fluorescent nanomaterials,which possess wide application prospects based and even beyond the fluorescence properties.Herein,we report the fast and high-yield synthesis of CDs and the large-scale preparation of fluorescent nanofiber films with enhanced mechanical properties.CDs were prepared from magnetic hyperthermia treatment of citric acid and carbamide,with the output of 25.37 g in a single batch.The asprepared CDs exhibit a high absolute photoluminescence(PL)quantum yield(QY)of 67%and wonderful dispersibility in polar solvents.Then,solution blow spinning of CDs and polymer matrixes of alcohol soluble polyurethane(APU)and polyacrylonitrile(PAN)led to large-area fluorescent CDs-embedded nanofiber films,APU/CDs(size:120 cm×18 cm)and PAN/CDs(size:120 cm×22 cm),respectively.The resultant large-area APU/CDs and PAN/CDs nanofiber films have dramatically enhanced mechanical properties,to show integrated improvement of tensile strength and elongation.