Graphical The upconversion luminescence intensity of LiErF 4 was enhanced by a suitable Gd 3+ content which is too low for LiGdF 4 synthesis. Considering the enhanced upconversion emission of LiErF 4 and synthesis of pure tetragonal phase LiGdF 4 , a core–shell structure of LiErF 4 @LiGdF 4 :Yb,Er was designed and a series of relevant derivatives with red-to-green tunable upconversion luminescence were obtained. In this study, LiErF 4 and related LiGdF 4 core-shell nanocrystals were synthesized via thermal decomposition, and the upconversion luminescence under an excitation of 980 nm was investigated. The phase of LiErF 4 was not changed by a low content of Gd 3+ dopant, whereas orthorhombic GdF 3 formed as an impurity when the amount of Gd 3+ was increased. The upconversion luminescence intensity of LiErF 4 was enhanced by a suitable Gd 3+ content. Considering the enhanced upconversion emission of LiErF 4 and synthesis of pure tetragonal phase LiGdF 4 , a core–shell structure of LiErF 4 @LiGdF 4 :Yb,Er was designed, characterized, and compared to LiYF 4 @LiGdF 4 :Yb,Er. LiErF 4 @LiGdF 4 :Yb,Er had a yellow upconversion emission output, which was attributed to the combination of the upconversions in the core and shell. Additionally, a series of relevant derivatives of LiErF 4 @LiGdF 4 :Yb,Er were prepared for further investigation of their luminescence performance, and red-to-green tunable upconversion luminescence was obtained for these core–shell nanocrystals.
Multimodal imaging can compensate for the deficiencies and incorporate the advantages of individual imaging modalities . In this paper, we demonstrated the synthesis of core–shell nanocomposites LiLuF 4 @LiGdF 4 :Yb,Er/Tm constituted of tetragonal LiLuF 4 nanoparticles as core and Yb,Er/Tm-codoped LiGdF 4 as shell. LiLuF 4 @LiGdF 4 :Yb,Er/Tm nanoparticles display brighter upconversion luminescence (UCL) than NaGdF 4 :Yb,Er/Tm nanoparticles with the same size under continuous-wave excitation at 980 nm. The active shell layer of LiGdF 4 :Yb,Er/Tm not only provide the UCL center, but also serve as magnetic resonance (MR) imaging contrast agent. To further improve the UCL intensity, the inert LiGdF 4 shell was coated on the LiLuF 4 @LiGdF 4 :Yb,Er/Tm nanoparticles. Furthermore, LiLuF 4 @LiGdF 4 :Yb,Tm@LiGdF 4 nanoparticles have been successfully applied to UCL/X-ray computed tomography (CT)/MR tri-modal imaging on the modal of tumor-bearing mice.
LiGdF4 nanoparticles (NPs) with different Ca2+ contents were synthesized by a thermal decomposition method. The as-prepared NPs were able to emit green and strong red light when excited by a 980 nm laser through a two-photon process and they were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectroscopy. Rietveld refinement was performed to explore the structure and phase composition of the product. It was found that Ca2+ ions were vital to the successful synthesis of LiGdF4 NPs and an appropriate Ca2+ content (ca. 19%) yielded the product with highest purity. The purity of the obtained product was highly correlated with the PL intensity and red/green light intensity ratio.
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