Enhancement mechanism of red upconversion emission in a single NaYbF₄:2%Er³⁺@NaYbF₄micron core-shell structure

Abstract

The construction of core-shell structure can effectively reduce the quenching effect on the surface of materials and realize the regulation of 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 were constructed with the help of epitaxial growth technology, which effectively enhanced the red upconversion emission of Er³⁺ions. The prepared microcrystals with core-shell structures are all hexagonal phase microdisks, and their sizes are relatively uniform. In order to better obtain the material spectral data, a confocal microscopic spectroscopy testing system was used to study spectral properties. Under 980 nm near-infrared laser excitation, the red emission intensity of single NaYbF₄:2%Er³⁺@NaYbF₄@NaYF₄core-shell-shell microdisk is 4.6 times higher than that of NaYbF₄:2%Er³⁺ micron disk, and the red-to-green ratio is increased from 6.3 to 8.1. Meanwhile, Ho³⁺ ions were introduced into the NaYbF₄:2%Er³⁺@NaYbF₄: 2%Ho³⁺@NaYF₄ core-shell-shell microdisk, and the red emission intensity was nearly 6.7 times higher than that of single NaYbF₄: 2%Er³⁺ microdisk, and the red-to-green ratio increased from 6.3 to 9.4 by means of ion-to-ion interaction. Through the study of microcrystal spectral characteristics and luminescence kinetics of different core-shell structures, 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 between Ho³⁺ ions to Er³⁺ ions. The micron core-shell structures with efficient red emission in this paper has great application prospects in the fields of luminescence, anti-counterfeiting and optoelectronic devices.