Preparation And Properties Of Rare Earth-doped Nanoparticles（LaF₃:Tb,Ce）

In recent years,the rapid development of Time-Resolved Fluorescence detection（TRF）has attracted extensive attention.Based on long-life fluorescent probes,TRF makes use of the Time-gate to effectively overcome the low sensitivity and poor accuracy of the traditional fluorescence detection technology caused by the interference of scattered light background noise and bioluminescence,significantly improving the detection accuracy,specificity and reliability.Due to these great advantages,TRF has been widely applied in scientific research and medical tests.Due to the unique optical properties such as sharp f-f emission peak,long fluorescence lifetime and large Stokes shift,rare earth nanoparticles have good prospects in application of time-resolved fluorescence detection.However,most of the conventional rare earth based time-resolved fluorescent probes are faced with poor fluorescence stability,poor anti-interference ability and low fluorescence quantum yield,which limit the detection sensitivity and accuracy.In this paper,a rare-earth nanoparticle LaF₃:Tb,Ce with good water solubility,high fluorescence stability and high quantum yield was synthesized by hydrothermal method.By adjusting the synthesis conditions of nanoparticles,the morphologies were optimized,the formation mechanism of nanoparticles was explored,and hexagonal-like porous nanoparticles with a uniform size of 35-40 nm were obtained.Based on the wide absorption in the UV region（4f-5d）and the large absorption cross section of Ce³⁺,taking advantage of the resonance energy transfer between Ce³⁺and Tb³⁺,Ce³⁺and Tb³⁺co-doping strategy was used to greatly improve the luminous efficiency of Tb-based fluorescent nanomaterials.The effects of Ce³⁺doping ratio on the structure and fluorescence properties of nanomaterials were systematically investigated.It was found that the doping of Ce³⁺extends the fluorescence lifetime of nanoparticles from 4.8 ms(without Ce³⁺doping)to 6.0 ms(with 40%Ce³⁺doping).The fluorescence quantum yield of nanoparticles increased with the increase of Ce³⁺doping ratio,and reached a maximum of 42.6%with 40%Ce³⁺doping and tended to balance.Compared to undoped Ce³⁺nanoparticles（QY=0.6%）,there was a 70-fold increase.The nanoparticles were further functionalized with polyacrylic acid（PAA）or O-Phosphorylethanolamine（AEP）to improve their stability and to coat the surface with active carboxyl or amino groups for further targeting modification.It was found that the modification had no significant effect on the structure and fluorescence properties of the nanoparticles.Finally,NHS-FITC and NHS-Cy3 were used as model dyes to couple with the aminated LaF₃:Tb,Ce@AEP nanoparticles.The FRET effect were investigated,and the FRET efficiencies between FITC/Cy3 and nanoparticles were calculated as 64.2%and 47.7%,respectively,by fluorescence lifetime measurement,demonstrating the feasibility of this system for multi-component detection based on time-resolved fluorescence.