Synthesis Of Strongly Luminescent And Highly Stable Cu(I) Metal Halides And Their Applications In Sensing

Copper（I）-based metal halides with formula of Cs₃Cu₂X₅（X=Cl,Br,I）have attracted substantial attention in the field of optoelectronics because of their excellent optoelectronic properties,abundant metal resources and low toxicity.They are considered as one of the promising candidates for next-generation solid-state lighting.However,poor stability of Cs₃Cu₂X₅ restricts their practical application due to the vulnerability of Cu（I）to oxidation.In addition,the main applications of Cs₃Cu₂X₅ are currently focused on optoelectronic devices,and few reports can be found in the literature on the application of Cs₃Cu₂X₅ in the construction of fluorescent sensor.Based on the above considerations,the highly stable and strongly luminescent Cs₃Cu₂X₅ was synthesized at room temperature and temperature（T）and dimethylamine（DMA）fluorescence sensor were successfully constructed in this work,broadening their application in the field of fluorescence sensing.The main research contents are as follows:（1）Highly stable and bright luminescent Cs₃Cu₂Cl₅ was synthesized using ascorbic acid（Vc）as organic ligand.Vc with antioxidant properties was firstly used as organic ligand to prepare Cs₃Cu₂Cl₅ by room temperature anti-solvent recrystallization method.Vc can accelerate the solubility of metal halides in the precursor solution and improve the reaction rate.The anti-oxidation property of Vc protected Cs₃Cu₂Cl₅ from being oxidised by oxygen in the environment.Meanwhile,Vc was coordinated to Cu⁺and passivated Cs₃Cu₂Cl₅ as organic ligand.Thus,using Vc could effectively improve the luminescence efficiency and stability of Cs₃Cu₂Cl₅.The experimental results showed that the obtained Cs₃Cu₂Cl₅ has～96.79%high photoluminescence quantum yields（PLQYs）and good air stability（Cs₃Cu₂Cl₅ maintained60.1%of photoluminescence emission efficiency after 12 days）,compared to the ligand-free Cs₃Cu₂Cl₅.This strategy effectively solved the problem of low PLQYs and poor air stability due to the easy oxidation of Cu⁺,and provided an idea for the preparation of highly stable and bright luminescent Cs₃Cu₂Cl₅.（2）A visual temperature sensor has been constructed based on the thermal quenching behavior of Cs Cu₂Cl₃ metal halide towards T.A two-phase mixture of Cs Cu₂Cl₃ and Cs₃Cu₂Cl₅ was synthesized via mechanical grinding method,which exhibited a high sensitivity to T due to thermal quenching phenomenon of Cs Cu₂Cl₃.In addition,due to Cs₃Cu₂Cl₅ exhibited fluorescence enhancement at high temperatures,the blue emission of Cs Cu₂Cl₃ was gradually quenching and showed the green emission of Cs₃Cu₂Cl₅ when T was increased,showing a colour change from blue to green under the 254 nm UV lamp.The experimental results showed that the fluorescence intensity of Cs Cu₂Cl₃ decreased as T increased under the optimal sensing conditions,and displayed a good linear relationship in the T range of 38-65°C.Hence,we have successfully constructed a sensitive,fast and visual temperature sensor that broadens the application of copper-based metal halides in the field of fluorescence sensing.（3）A ratiometric DMA fluorescence sensor was constructed based on the specific response of Cs₃Cu₂I₅ to DMA.The portable Cs₃Cu₂I₅ film was prepared by solvent evaporation crystallization method.When DMA gas was introduced,Cu I in Cs₃Cu₂I₅ reacted with DMA to form a new fluorescent substance[C₂H₇N]₄-Cu₄I₄,and a new fluorescence emission peak appeared at 598 nm.With increasing DMA concentration,the fluorescence intensity of the Cs₃Cu₂I₅ film at 443 nm gradually decreased,and the fluorescence intensity at598 nm gradually increased.The fluorescence colour of Cs₃Cu₂I₅ film changed from blue to orange-red,which enables ratiometric fluorescence sensing and visual detection of DMA.The results showed that the fluorescence intensity ratio I₅₉₈/I₄₄₃ exhibited good linearity in the DMA concentration range of 13-40 ppm under optimal sensing conditions.Furthermore,the excellent selectivity of the sensor for DMA provides a new strategy to achieve the detection of DMA in the atmosphere.