Photoluminescence Control And Fluorescence Sensing Application Of CsPbX₃（X=Cl，Br） Quantum Dots

All-inorganic perovskite Cs Pb X₃（X=Cl,Br,I）quantum dots（QDs） have attracted attention due to their excellent photoelectric properties.For example,high photoluminescence quantum efficiency（PLQY）,adjustable emission wavelength,high color purity,strong light absorption,etc.Compared with inorganic/organic hybrid perovskite QDs,Cs Pb X₃ QDs have higher stability.Therefore,they have shown a wide range of applications in the fields of lighting and display,solar cells,and fluorescent sensing,etc.However,Cs Pb X₃ QDs have still some urgent problems to be solved,such as poor stability,lead toxicity,and low PLQY of blue Cs Pb Cl₃QDs.Based on the excellent optical properties of Cs Pb X₃ QDs,this paper designed a method based on Cs Pb Br₃（CPB）QDs as fluorescent probes for detecting Cu²⁺in aqueous solutions.In addition,the performance of Cs Pb X₃ QDs is improved by doping with alkali metal ions.In this work,Cs Pb X₃ QDs doped with alkali metal ions were successfully prepared and their physical and chemical properties were studied.For the purpose of improving the PLQY of blue light Cs Pb Cl₃,Sr²⁺single-doped and K⁺/Sr²⁺co-doped Cs Pb（Br/Cl）₃ perovskite QDs were prepared in this work..The research results show that the doping engineering strategy effectively improves the PLQY of perovskite QDs.The main research contents this paper include:An ingenious way to detect Cu²⁺in aqueous solution based on the CPB QDs is reported.By adding OAm with strong coordination ability,Cu²⁺ions can be selectively transferred from water to cyclohexane,thereby quenching the fluorescence of CPB in the organic phase.Typically,both freshly prepared CPB QDs and OAm are firstly dissolved in cyclohexane and then the CPB（OAm）solution is mixed with Cu²⁺aqueous solution.With mixing for 1 min on a vortex mixer,OAm in cyclohexane can capture Cu²⁺from water to form Cu²⁺-OAm complexes at the interfaces of cyclohexane/water,since the amine-rich ligands have strong coordination with metal ions.These Cu²⁺complexes can rapidly diffuse into cyclohexane and finally quench PL of the CPB QDs.This method avoids the direct application of perovskite QDs,which are unstable to water,in aqueous environments through the Cu²⁺phase transfer strategy.In addition,CPB as a fluorescent probe shows a wide linear range(10^-6 M-10^-2 M),short response time（1 min）and good selectivity to Cu²⁺.Through cation and anion exchange reaction at room temperature Sr and Cl co-doping of CPB QDs is realized.The effects of Sr²⁺doping on the structure,composition and optical properties of QDs were studied by XRD,TEM and spectroscopy techniques.The results showed that the Sr²⁺doping rate was 0.36%by EDS quantitative analysis.The introduction of Sr²⁺has almost no effect on the emission and absorption spectra of QDs.At the same time,Sr²⁺doping can increase its PLQY.This may be due to the fact that Sr²⁺replaces Pb²⁺with a similar radius,reducing Pb vacancies,thereby reducing surface defects,resulting in an increase in the PLQY of QDs.In addition,the blue shift of both emission and absorption spectra is mainly due to the substitution of smaller radius Cl^-for larger radius Br^-.A multi-cation synergistic doping strategy is proposed.The K⁺/Sr²⁺co-doped blue Cs Pb（Br/Cl）₃ QDs（460 nm-470 nm）were successfully prepared using an improved thermal injection method.The presence of K⁺/Sr²⁺in QDs was confirmed by TEM,EDS,XRD and XPS.Among them,Sr²⁺are incorporated into the perovskite lattice to partially replace Pb²⁺,causing slight lattice shrinkage.In addition,part of K⁺forms a potassium halide passivation layer on the surface of the QDs,which can effectively passivate the surface defects of the QDs,thereby improving their PLQY and prolonging the life of the PL.