Core-mediated synthesis, growth mechanism and near-infrared luminescence enhancement of α-NaGdF4@β-NaLuF4:Nd3+ core–shell nanocrystals

Abstract

Lanthanide doped hexagonal phase (β) rare earth fluoride (NaREF₄) nanocrystals have considerable potential in laser and, especially, biological applications. However, their large size and extreme synthetic conditions have become unavoidable obstacles in their path to various applications. Herein, a core-mediated hetero-shell growth method was adopted to synthesize α-NaGdF₄@β-NaLuF₄:Nd³⁺ nanocrystals, in which cubic phase (α) NaGdF₄ was used as the core to induce the subsequent growth of a β-NaLuF₄:Nd³⁺ shell via a two-step solvothermal reaction. The resulting α-NaGdF₄@β-NaLuF₄:Nd³⁺ core–shell nanocrystals were characterized by structural analysis, photoluminescence spectroscopy and decay lifetime. Besides, a persuasive lattice-disordered heterointerface-induced mechanism was proposed to understand the core-mediated hetero-shell growth. Meanwhile, the influence of the heterointerface on the dynamic growth of the shell nanocrystals was also investigated in detail. Most importantly, the near-infrared luminescence intensity at 1.06 μm was enhanced by over two times via coating the lattice-matched homogeneous NaLuF₄ shell on the surface of α-NaGdF₄@β-NaLuF₄:Nd³⁺ nanocrystals. The high-performance α-NaGdF₄@β-NaLuF₄:Nd³⁺ nanocrystals thus obtained are expected to be used for laser output and depth detection of biological tissues.