Synthesis Of NaYF₄:Yb,Er And Its Application In Fe³⁺ And Al³⁺ Ions Detection

Fluorides are ideal host selective materials for upconversion luminescence materials because of their very low phonon energies and high chemical stability,particularly Yb³⁺/Er³⁺or Yb³⁺/Tm³⁺ doped NaYF₄ is one of the most efficient upconversion luminescence material.Rare-earth doped upconversion luminescence materials can convert near-infrared excitation to UV or visible emission with great advantages,such as a large anti-Stokes shift,superior photostability,high penetration depth and no autofluorescence?noise?from biological specimens,so it is an ideal material for application of in vivo detection.Upconversion luminescence materials have great potential applications in bioimaging,bio-detection,drug delivery,photodynamic therapy and cell molecule interaction study.Various metal ions play a key role in environmental and biological processes,such as Fe³⁺ and Al³⁺ ions.Therefore development of effective detection method of Fe³⁺ and Al³⁺ ions in environment and biological samples is very important.This paper designed to prepare NaYF₄:Yb,Er UCNPs which have main red and green emission respectively by thermal decomposition and coprecipitation method.In order to detect ions this paper treated as-prepared UCNPs with hydrophilization to obtain nanoparticles of good water dispersibility and then combined them with two ion probes to detect Fe³⁺ and Al³⁺ ions.Firstly,this paper prepared upconversion luminescence material with strong red light emission using thermal decomposition through adjusting the molar proportion of the two ligands and coating shell.By using hydrochloric acid to remove surface ligand of UCNPs,this paper obtained ligand-free UCNPs with good water dispersibility and positive surface charge,which can adsorb 3,3?,5,5?-tetramethylbenzidine?TMB?to form TMB-UCNPs composite probe through electrostatic interaction to detect Fe³⁺ ion,the results show that fluorescence intensity of TMB-UCNPs decreased almost linearly with the amount of Fe³⁺ from 0 to 40 ?M,the detection limit is 0.22 ?M.At the same time,this composite probe has good selectivity for the detection of Fe³⁺ ion and the presence of other ions have almost no influence on Fe³⁺ ion detection.When using hydrophilic UCNPs with strong green light emission for Fe³⁺ ion detection,fluorescence intensity of TMB-UCNPs decreased almost linearly with the amount of Fe³⁺ from 0 to 70 ?M,the detection limit is 0.08 ?M.Then this paper synthesized NaYF₄:Yb,Er@NaYF₄ core-shell structure by coprecipitation method,the coating of inert shell improved luminescence intensity of upconversion materials in a large extent.This paper obtained mesoporous and hydrophilic UCNPs@mSiO₂ by three steps including the phase transfer of hydrophobic UCNPs,the coating of silica and the remove of template,then combined it with as-prepared dye Rhodamine B derivative to detect Al³⁺ ion.The results show that fluorescence intensity of UCNPs@mSiO₂-RBP decreased almost linearly with the amount of Al³⁺ from 0 to 50 ?M,the detection limit is 0.16 ?M.Cu²⁺ is interference ion for detection and responsiveness of Cu²⁺ is higher than Al³⁺.Therefore,this composite probe is applied to detect Cu²⁺,the results show that fluorescence intensity of UCNPs@mSiO₂-RBP decreased almost linearly with the amount of Cu²⁺ from 0 to 18 ?M for Cu²⁺ ion detection,the detection limit is 0.13 ?M and the detection has good selectivity.