Construction And Analysis Of Cyanine Dyes Sensitized NaGdF₄:Yb,Er@NaGdF₄:Yb,Nd Upconversion Nanomaterial Luminescence System

Lanthanide-doped upconversion nanoparticles（UCNPs）can convert near infrared（NIR）light into ultraviolet and visible light.Because of their good chemical and optical stability,narrow emission peaks,low autofluorescence background,low toxicity,large anti-Stokes shift and longer fluorescence lifetime,they have attracted more and more researchers’attention.Because Nd-doped UCNPs have low absorption efficiency under 808nm laser,they emit weak light.The cyanine dyes can absorb the energy from the 808 nm laser and transfer it to UCNPs,thereby enhancing the luminescence of the UCNPs.Based on the sensitization efficiency of different dyes in water and their recognition groups,two cyanine dyes were designed and synthesized in this paper.At the same time,NaGdF₄:Yb,Er@NaGdF₄:Yb,Nd UCNPs with good dispersion and uniform particle size were synthesized by co-precipitation method.Three luminescent systems based on cyanine dye-sensitized UCNPs were established to achieve the detection of water content in organic solvents and quantitative detection of sulfide(S^2-)and hypochlorite（ClO^-）.（1）The core-shell Na GdF₄:Yb,Er@NaGdF₄:Yb,Nd UCNPs were successfully prepared by co-precipitation method,and the ligand exchange reaction between NOBF₄ and nanoparticles was used to improve water solubility of UCNPs.The dye IR-783 with negative charge and NOBF₄-UCNPs with positive charge are connected together by electrostatic action to sensitize UCNPs.However,Na₂S is in aqueous solution,S^2-is converted into H₂S and a highly selective reaction between IR-783 and H₂S blocked the sensitization process,which led to luminescence quenching.Based on this,a sensing system for S^2-detection is constructed.The detection linear range is 0.5～15μM,and the detection limit is 34.17 nM.（2）The sensitizer dye IR-808 was synthesized and used to sensitize NaGdF₄:Yb,Er@NaGdF₄:Yb,Nd UCNPs.Based on the fact that the energy transfer efficiency between dye IR-808 and UCNPs in water is much lower than that in organic phase.Therefore,when the dye-sensitized nanoprobe is added to organic solvent containing water（such as N,N-dimethylformamide（DMF）,dimethyl sulfoxide,methanol,acetone,acetonitrile and ethanol）,the luminescence intensity at 545 nm is significantly reduced.The experimental results show that the reduction of the luminescence intensity at 545 nm has a linear relationship with the ratio of the water content in the organic solvent.Based on this,the method for measuring the water content in several organic reagents has been established.This method can detect water content of 0.05%to 10%（volume%）,and the detection limit in DMF is 0.018%.（3）A sensitizer dye IR-806 was synthesized and used to sensitize the luminescence of NaGdF₄:Yb,Er@NaGdF₄:Yb,Nd UCNPs.In the presence of sodium hypochlorite（a ClO^-donor）,the thiol group of IR-806 was oxidized,which weakened the dye’s absorption ability and led to the luminescence quenching,which realized the detection of ClO^-.Based on this,a sensing system for detecting ClO^-was constructed.The linear range of this system for detecting ClO^-is 0.067 to 11.55μM,and the minimum detection limit is 0.046μM.