Study On The Upconversion Luminescence Mechanism And Color Tuning Of Er³⁺ And Tm³⁺ Under Different Excitation Wavelengths

Color-tunable rare earth nanocrystals have broad application prospects in the fields of ultra-high resolution display,multi-dimensional security design,and multi-channel bioluminescence detection.This article focuses on the hot spot of"realizing tunable three-primary color fluorescence at the single particle level",and strives to solve the problem that color tuning requires a highly complex excitation system and operation.Based on the rare-earth-doped NaYF₄ upconversion luminescence materials,under different excitation wavelengths,the up-conversion luminescence mechanism and color tuning performance of Er³⁺and Tm³⁺have been studied.The main research contents are as follows:Hexagonal NaYF₄（β-NaYF₄）samples doped with different concentrations of Er³⁺were synthesized by hydrothermal method,and a five-level model suitable for 980 nm excitation and an eight-level model suitable for 1530 nm excitation were constructed to calculate the theoretical slope of Er³⁺upconversion luminescence power relationship.The up-conversion luminescence mechanisms of Er³⁺under 980 and 1530 nm excitation were revealed.A new energy cycle mechanism was designed to improve the upconversion luminescence intensity of lanthanide ion by introducing Yb³⁺as an energy reservoir,and the effectiveness of the energy cycle mechanism was analyzed through the theory of rate equation model.A³⁺(A³⁺=Tm³⁺,Er³⁺)single-doped and A³⁺/Yb³⁺co-dopedβ-NaYF₄ nanocrystals were prepared by an improved thermal decomposition method.The effect of Yb³⁺on the upconversion fluorescence efficiency of Er³⁺and Tm³⁺was investigated through spectral testing.The effectiveness of the designed energy cycle mechanism was verified experimentally.Nanocrystals with multi-layer core-shell structure were designed to emit green and red light under the excitation of 980 nm laser with different power,and blue light under the excitation of 800 nm laser,respectively.The seed crystal nucleus were prepared by thermal decomposition method,and then the subsequent multilayer core-shell structure upconversion nanocrystals were prepared by the one-pot method.The three-primary color tuning performance of the nanocrystals of Er³⁺and Tm³⁺excited by dual wavelength was studied,and the feasibility and specific luminescence mechanism of the three-primary color nanocrystals were verified by experiments.