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

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.