Design Of Rare Earth Doped NaREF 4 (RE=Y/Gd) Nanocrystalline Core-shell Structure And Its Upconversion Luminescence Properties

In recent years,rare earth have been widely used because of their abundant energy levels and special 4f electronic layer structure.The rare earth doped upconversion luminescent nanomaterials have attracted much attention from researchers because of their potential applications in biological imaging,optical display and fluorescent probe.Due to its low phonon energy,good light permeability and high chemical stability,rare earth fluoride has become the most efficient substrate material.The rare earth doped fluoride nanocrystals have become the research focus,which is beneficial from their excellent upconversion luminescence efficiency and small size.In this paper,the synthesis of rare earth doped fluoride nanocrystals and the construction of the core shell structure have been studied.The main contents of this paper are as follows:First of all,the cubic phase NaYF4 nanocrystals have been synthesized by simple and convenient hydrothermal method,and the upconversion luminescence has been achieved by the incorporation of Yb3+ and Ho3+.Five samples have been obtained by changing the reaction time and the enhancement of luminescence has been observed by the phase analysis,TEM analysis and upconversion luminescence spectra analysis.The preparation of the hexagonal NaYF4 by coprecipitation method with controlling the reaction conditions(reaction time and temperature)is benefitial to increase the luminesect efficiency.The best activator and sensitizer doping concentration have been obtained and the upconversion mechanism has been explored by changing the Yb3+ and Ho3+ concentration.The structure analysis indicates the ?-NaYF4 nanocrystals possesed the more efficiency upconversion emission.By coprecipitation method,the hexagonal NaYF4 with uniform size and good dispersion were successfully synthesized.The quenching effect of the luminescence centers is easy to occur,due to the small size of the nanoparticles.The core-shell structure is beneficial to weaken the surface quenching effect,and then improves the upconversion efficiency.The luminescence efficiency has been improved by preparing core-shell structure.And the heterogeneous nuclear shell structure NaYF4@SiO2 has been obtained,which can acieve the hydrophilic property of nanoparticles.It is more conducive to the application of in vivo.The final synthesis is more suitable for ultra small NaGdF4:Yb3+/Er3+ nanoparticles used in fluorescent probes,based on core-shell structure constructed nanoparticles with double shell,NaGdF4:Yb3+Er3+@NaGdF4:Yb3+@NaGdF4:Nd3+ samples by 980nm and 808nm double excitation.The middle layer can effectively prevent the back energy transfer process between the activator ion Er3+ and sensitizer ion Nd3+ by the middle shell.Meanwhile,as a bridge the Yb3+ions can enhance the upconversion luminescence,and explore the luminescence mechanism of Nd3+-Yb3+-Er3+ through the experiment.Thus,in this paper,the efficiency upconversion nanoparticles have been obtained,which are more favorable to biomedical applications.