Energy transfer characteristics of single-particle NaYF₄ core-shell structure

Abstract

The construction of rare-earth doped micro/nano core-shell structure is not only beneficial to enhance the upconversion emission intensity, but also can realize the fine control of luminescence color through the spatial separation of ions. In this work, a series of NaYF<sub>4</sub>@NaYF<sub>4</sub> core-shell (CS) microcrystals doped with different ion concentrations were constructed by means of epitaxial growth technology. The structure and morphology of the prepared microcrystals were characterized by X-ray diffractometer (XRD) and scanning electron microscope (SEM). The experimental results show that the prepared CS structures had a pure hexagonal-phase crystal structure, and exhibited a disk-like shape. Under the excitation of 980 nm laser, the energy transfer characteristics of doped ions in single CS microcrystals were carefully studied by using a confocal microscope spectroscopy test system and changing the excitation position. The study shows that the ions doped in different regions of the CS microdisks exhibit different spectral characteristics when the excitation position is changed, which is mainly due to the different directions of excitation energy transfer in the CS structure. Based on the emission spectra of different positions and power variation spectra, it is proved that the excitation energy of the micron CS is mainly transmitted from outside to inside. Meanwhile, the colorful emission pattern of the CS microdisk is revealed by the corresponding optical waveguide model, which is mainly due to the Optical waveguide effect. Therefore, by constructing different micron core-shell structures, the luminescence characteristics of microcrystals can be controlled and adjusted, and the application of microcrystals in optoelectronic devices, optical coding and multicolor display can be provided with important experimental reference.