Enhancement mechanism of red up-conversion emission in single NaYbF₄:2%Er³⁺@NaYbF₄ micron core-shell structure

The construction of core-shell structure can effectively reduce the quenching effect on the surface of material and regulate ion-ion interaction, which has become one of the effective ways to enhance and regulate the spectral characteristics of rare-earth upconversion luminescent materials. In this paper, a variety of NaYbF4:2%Er3+ micron core-shell structures are constructed with the help of epitaxial growth technology, effectively improving the red up-conversion emission of Er3+ ions. The prepared microcrystals with core-shell structures are of hexagonal phase microdisks, and their sizes are relatively uniform. In order to better obtain the material spectral data, a confocal microscopic spectroscopy is used to study spectral properties. Under 980 nm near-infrared laser excitation, the red emission intensity of single NaYbF4:2%Er3+@NaYbF4@NaYF4 core-shell-shell microdisk is 4.6 times higher than that of NaYbF4:2%Er3+ micron disk, and the red-to-green ratio increases from 6.3 to 8.1. Meanwhile, Ho3+ ions are introduced into the NaYbF4:2%Er3+@NaYbF4: 2%Ho3+ @NaYF4 core-shell-shell microdisk, and the red emission intensity is nearly 6.7 times higher than that of single NaYbF4:2%Er3+ microdisk, and the red-to-green ratio increases from 6.3 to 9.4 through the interaction between ions. The microcrystal spectral characteristics and luminescence kinetics of different core-shell structures are studied, showing that the red emission enhancement of Er3+ ions is mainly derived from the construction of different core-shell structures, which can effectively enhance the cross-relaxation between Er3+ ions, the energy back transfer between Yb3+ and Er3+ ions, and the energy transfer from Ho3+ ions to Er3+ ions. The micron core-shell structures with efficient red emission in this study has great application prospects in the fields of luminescence, anti-counterfeiting and optoelectronic devices.