Preparation Of NaYF₄:Yb³⁺/Er³⁺/Zn²⁺ And Single Particle Fluorescent Probe The Study

Rare-earth ions are one of the research hotspots in the field of luminescence because they have many unique optical properties such as sharp emission line and long fluorescence lifetime.Rare earth doped up-conversion materials can convert two or more low energy photons into one high energy photon.Because low photon energy infrared light penetrates deep into biological tissues and has low background fluorescence,rare earth doped up-conversion materials excited by infrared light are often used in the fields of in vivo imaging,photothermal therapy,and biochemical detection.However,the rare earth-doped nanoparticles have a relatively low luminescence efficiency,which limits their application,especially in the detection of trace elements and the development and utilization of single-particle fluorescence probe.Therefore,preparation of rare earth doped nanoparticles with high quantum yield is of great significance for enhancing their practical applications.In this paper,luminescence enhanced NaYF4:Yb3+/Er3+/Zn2+ up-conversion nanoparticles were prepared by incorporating Zn2+ ions in combination with a hydrothermal method.Surface modification of the nanoparticle was carried out with branched polyethyleneimine and a kind of high sensitivity single-particle fluorescence probe for the copper ions detection was developed.The specific research work is as follows:1.The NaYF4:Yb3+/Er3+ hexagonal disc microparticles with uniform morphology and uniform size were prepared by hydrothermal method.By introducing Zn2+ ions,the size of NaYF4:Yb3+/Er3+ microparticles is reduced from 1.02 ?m to 320 nm.The single NaYF4:Yb3+/Er3+ microparticle and NaYF4:Yb3+/Er3+/Zn2+ nanoparticle were observed and studied.It was found that the overall luminescence intensity of the single NaYF4:Yb3+/Er3+/Zn2+ nanoparticle was significantly stronger than that of NaYF4:Yb3+/Er3+,the blue and green emission were enhanced 176 and 45 times,respectively.2.The single-particle fluorescence probe for high-sensitivity detection of copper ions were successfully prepared by surface modification of the NaYF4:Yb3+/Er3+/Zn2+nanoparticle with branched polyethyleneimine(PEI).The results showed that the rare earth doped nanoparticle with higher luminescence efficiency was beneficial to improve the linear response range of the fluorescent probe to copper ions.The smaller size of rare earth doped nanoparticle facilitates the single-particle fluorescence probe to achieve lower detection limits of copper ions.By linear fitting,the detection limit for this single-particle fluorescent probe was found to be around 11 nM and the linear range was 20 nM-60 nM.3.Combined with the rare-earth ion luminescence resonance energy transfer,the mechanism of the single-particle fluorescence probe luminescence quenching caused by copper ions was studied.The approach to obtain lower detection limit for the single-particle fluorescence probe and the possibility of applying high-sensitivity detection of more heavy metal ions ware explored.