Synthesis of LiErF4 and LiGdF4 Core-Shell Nanocrystals and Tunable Upconversion Emission from Red to Green

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.