Upconversion luminescence characteristics of Ho<sup>3+</sup> ion doped single-particle fluoride micron core-chell structure
Acta Physica Sinica(2022)
Abstract
Constructing core-shell structures can effectively reduce the surface quenching effect of luminescent materials, which becomes an effective method to enhance upconversion luminescence. In this work, a series of NaLnF4@NaLnF4 (Ln = Y3+, Yb3+, Ho3+) core-shell microcrystals is successfully synthesized based on epitaxial growth technology, thereby enhancing and regulating the upconversion emission of Ho3+ ions. The results of the XRD and SEM indicate that the NaLnF4@NaLnF4 core-shell microcrystal possesses a pure hexagonal-phase crystal structure with a rod-like shape. Meanwhile, it is found that the epitaxial growth direction of the micro-shell is not affected by the crystal characteristics in the core, but determined by the crystal characteristics of the shell. Under 980 nm near-infrared laser excitation, the upconversion luminescence properties of single microrods with different core-shell structures are investigated via a confocal microscope spectroscopy. It is found that in the NaLnF4 micro-crystal, the coated NaYF4 inert shell can also effectively reduce the quenching effect on the surface of the micro-crystal for enhancing upconversion emission. When the Yb3+ ions are introduced into NaYF4 or NaYbF4 active shell that is coated, the Yb3+ ions in the shell can effectively transfer excitation energy to Yb3+ in the core through energy migration, and then establish new energy transfer channels, thereby realizing the Ho3+ ion luminescence enhancement. For NaHoF4@NaYbF4 core-shell microrods, the Yb3+ in the shell can transfer more excitation energy to Ho3+ ions at the adjacent interface for enhancing the overall luminescence intensity, and its higher red-green ratio is mainly due to the cross-relaxation process occurring between the Ho3+ ions at high doping concentration of Ho3+ in the NaHoF4 core. Meanwhile, the luminescence process of the micron core-shell system is further confirmed based on the luminescence characteristics of different structures and the dynamic luminescence process. It can be seen that constructing different micron core-shell structures and introducing sensitizing ions, can not only effectively enhance the luminous intensity of the micron materials, but also adjust the output color. Therefore, this research is an important experimental reference for enhancing the luminous intensity of the micron system and the precise adjustment of luminescence, and can effectively expand the applications of micron crystals in the fields of displays, micron lasers and anti-counterfeiting.
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Key words
upconversion luminescence,micron core-shell structure,luminescence regulation,energy transfer,single particle
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