Synthesis of Multicolor Core/Shell NaLuF 4 :Yb 3+ /Ln 3+ @CaF 2 Upconversion Nanocrystals

摘要

The ability to synthesize high-quality hierarchical core/shell nanocrystals from an efficient host lattice is important to realize efficacious photon upconversion for applications ranging from bioimaging to solar cells. Here, we describe a strategy to fabricate multicolor core @ shell α-NaLuF 4 :Yb 3+ /Ln 3+ @CaF 2 (Ln = Er, Ho, Tm) upconversion nanocrystals (UCNCs) based on the newly established host lattice of sodium lutetium fluoride (NaLuF 4 ). We exploited the liquid-solid-solution method to synthesize the NaLuF 4 core of pure cubic phase and the thermal decomposition approach to expitaxially grow the calcium fluoride (CaF 2 ) shell onto the core UCNCs, yielding cubic core/shell nanocrystals with a size of 15.6 ± 1.2 nm (the core ~9 ± 0.9 nm, the shell ~3.3 ± 0.3 nm). We showed that those core/shell UCNCs could emit activator-defined multicolor emissions up to about 772 times more efficient than the core nanocrystals due to effective suppression of surface-related quenching effects. Our results provide a new paradigm on heterogeneous core/shell structure for enhanced multicolor upconversion photoluminescence from colloidal nanocrystals.