Synthesis Of Cs₃Cu₂X₅ NCs And Their Applications In Optical Fields

Cesium copper halides with the formula of Cs₃Cu₂X₅ NCs(X=Cl,Br,I)have recently received unparalleled attention in the field of optoelectronic and photovoltaic applications because of their superior properties,including high photoluminescence quantum yield(PLQYs),strong self-trapped exciton emission,and efficient Stokes shift.However,the Cs₃Cu₂X₅ NCs have crystal imperfections and poor stability,which affects their performance of optoelectronic devices,and limits their applications of fluorescence sensing,analysis and detection.Therefore,it is of great significance to prepare Cs₃Cu₂X₅ NCs with excellent performance and high stability.In this work,the Cs₃Cu₂X₅ NCs with high luminous efficiency,high PLQYs and high stability were prepared by the strategies of dual-passivation and using deep eutectic solvent(DES)as novel antisolvent.Moreover,we have successfully applied the Cs₃Cu₂X₅ NCs to the field of fluorescence sensing and analytical detection to achieve high-sensitivity detection of Fe³⁺,NH₃.The main research contents are shown below:(1)The dual-passivated Cs₃Cu₂X₅ NCs with high luminous efficiency,high PLQYs and high stability was prepared by using a novel double passivation.This double passivation was firstly established by using potassium oleate(K-OA)as passivator,K ion is used as ion-doping passivation and OA ion is used as the organic ligand,suppressing the intrinsic and surface defects of NCs.Compared to the free passivated NCs,the PLQYs of dual-passivated Cs₃Cu₂X₅(X=Cl,Br and I)NCs increase significantly from 2.87%,11.6%and 49.4%to 31%,69.9%,and 97.2%,respectively.Moreover,the stability of proposed NCs is greatly improved(Cs₃Cu₂Cl₅ NCs maintain 63%of PL efficiency after 100 hours,Cs₃Cu₂Br₅ and Cs₃Cu₂I₅ NCs maintain 65%and 97%of PL efficiency after 100 days,respectively)at 50-86%relative humidity and room temperature under ambient atmosphere.Furthermore,K-OA-passivated Cs₃Cu₂I₅ NCs was used as phosphors to fabricate blue-light LED,which emits high-quality blue emission.It shows great potential in the fields of blue light devices and lasers.(2)Cs₃Cu₂I₅ nanocrystals with high purity and high crystallinity were prepared by using hydrophobic DES with adjustable polarity as novel anti-solvent,and used as fluorescence probe to realize a high-sensitivity detection of Fe³⁺in environmental water samples.In this work,DES was prepared by using lauric acid(LA),capric acid(CA),tri-n-octylphosphorus(TOPO),and was firstly used to replace traditional antisolvents(toluene,methanol)to prepare Cs₃Cu₂I₅ NCs with high purity phase and high crystallinity,improving the problems of traditional antisolvents:such as toxicity and non-adjustable polarity.Compared with the NCs obtained by traditional anti-solvents,the NCs obtained by DES exhibited high PLQYs,long fluorescence lifetime,and shown excellent dispersion and stability.Moreover,benefited from the hydrophobicity of DES and the strong complexing ability between metal ions and DES,DES was used as extractant,Cs₃Cu₂I₅ NCs was used as fluorescent probe to construct Fe³⁺fluorescence sensor.With a certain concentration of Fe³⁺,fluorescence quenching of Cs₃Cu₂I₅ NCs was induced by the strong interaction between Fe³⁺and TOPO around Cs₃Cu₂I₅ NCs.Therefore,the relationship between Fe³⁺concentration and the fluorescence intensity of Cs₃Cu₂I₅ NCs was established to realize the detection of trace Fe³⁺in environmental water samples.The result shown that the proposed Fe³⁺fluorescent sensor obtained low detection limit(0.0034 ppm),and shown high sensitivity and selectivity.(3)An ammonia gas(NH₃)fluorescence sensor with high selectivity and high sensitivity was established based on Cs₃Cu₂I₅-DES film.The DES with abundant carboxyl functional groups and freezing point was prepared by using LA,CA,and was used as anti-solvent to synthesize Cs₃Cu₂I₅ NCs.Benefited from the solidifycation of DES at room temperature,the Cs₃Cu₂I₅-DES sensing film was made to realize the highly sensitive detection of NH₃ in the air.In the atmosphere of a certain NH₃ concentration,the carboxyl groups on the Cs₃Cu₂I₅-DES film react with NH₃ through proton exchange,and the fluorescence intensity of Cs₃Cu₂I₅ NCs decreases significantly.Therefore,the relationship between the concentration of NH₃ and the fluorescence intensity of Cs₃Cu₂I₅ NCs was established to achieve the highly sensitive detection of NH₃.The Cs₃Cu₂I₅ NCs are embedded and encapsulated on the surface and interior of the hydrophobic DES,enabling sensing film to exhibit good stability and water stability.Compared with the reported NH₃ fluorescence sensor,the sensor obtained short response time,low LOD(0.0012ppm),and showed excellent sensitivity and selectivity.This work greatly improves the phenomenon of poor selectivity and low sensitivity of traditional NH₃ fluorescence sensing,expanded the application of Cs₃Cu₂I₅ in the field of fluorescence sensing,provided a new idea for the detection of toxic gases by using copper-based halides.