Yb³⁺/Er³⁺ Co-doped NaYF₄ Nanocrystalline Core-shell Structure And Its Fluorescence Properties

With the continuous development of rare earth resources and the development of the back-end industrial chain,rare earth up-converting luminescence materials have received extensive attention.At present,rare earth luminescence materials have broad application prospects in medical imaging fields such as photodynamic therapy,biological monitoring,and biological imaging.However,currently low luminescence efficiency is still one of the main factors restricting its application.Fluoride has become a popular host material for rare earth doping due to its extremely low phonon energy and excellent chemical stability.In this paper,NaYF₄,which is widely recognized as having a high luminescence efficiency,is selected as the matrix to prepare two crystal phases of NaYF₄: Yb/Er nanocrystals and small-sized α-phase nanocrystals were used for shell coating.While achieving the purpose of luminescence enhancement,the effect of the core-shell structure on the temperature measurement characteristics and fluorescence lifetime of the material was explored.This article mainly includes the following contents:First,NaYF₄: Yb/Er nanocrystals were prepared using two methods of hydrothermal and solvothermal.And the optimal doping ratio of Yb/Er is explored to avoid the concentration quenching effect on the light intensity of the material.NaYF₄: Yb/Er nanocrystals with different crystal phases were prepared by adjusting the reaction temperature.α-NaYF₄ was prepared at a reaction temperature of 310 ℃ and below.The energy barrier was broken at 315 ℃,and the α phase was converted to Phase,β-NaYF₄ was prepared.Through spectral characterization,it was found that the green light of β-NaYF₄ nanocrystals is 402 times stronger than that of α-NaYF₄ nanocrystals.The red light is enhanced by 60 times.Then,NaYF₄: Yb/Er @ NaGdF₄ core-shell structure was designed and prepared by solvothermal method.During the experiment,the experimental procedure has been optimized to improve the success rate of the experiment.The light is enhanced by 2.8 times,and the green light is enhanced by 12.5 times.Based on the enhancement of the luminescence intensity of the core-shell structure,the influence of the core-shell structure on the fluorescence lifetime of the material was explored.Through the analysis of the fluorescence lifetime of the core NaYF₄: Yb/Er and the core-shell structure NaYF₄: Yb/Er @ NaGdF₄,the analysis found that The core-shell structure shows an enhanced effect on the fluorescence lifetime of red light and green light,and the enhancement ratio is 20%.The main reason is that the passivation effect of the growth of the shell layer on the surface defects of the core nanocrystals optimizes the way of energy transfer and reduces The occurrence of surface quenching occurred.Finally,the core-shell structure NaYF₄: Yb/Er @ NaGdF₄ of the inert shell and the core-shell structure NaYF₄: Yb/Er @ NaGdF₄: Yb of the active shell were prepared separately,The concentration of Yb³⁺ ions in the active shell was adjusted It was found that the excessively high concentration of Yb³⁺ ions in the shell layer resulted in a decrease in luminescence intensity.Next,the effect of shell thickness on the optical performance of the core-shell structure was explored,and it was found that the luminescence enhancement effect showed a trend of increasing first and then decreasing as the thickness of the shell increased.Through the thermal coupling level temperature measurement performance of the prepared core-shell structure,it was found that the core-shell structure has a significant improvement in the temperature measurement sensitivity of the material.