A novel one-pot strategy to rapidly synthesize bright red emitting upconversion nanocrystals with core–shell–shell structure
β-NaErF4:0.005Tm upconversion nanocrystals (UCNCs) with core–shell structure are quite popular due to efficient red upconversion luminescence. However, the traditional seed-mediated growth method is not continuous and quite time consuming, while the successive layer-by-layer strategy is unfriendly because of the usage of toxic sodium trifluoroacetate (Na-TFA). In this work, we utilized a novel one-pot strategy to synthesize β-NaErF4:0.005Tm with core–shell–shell structure. The morphology of the core could be significantly regulated. NaYbF4 and NaYF4 shells could be epitaxially grown on the core by simply adding fresh raw materials and heating to 300 °C, successively. Thanks to the suppression of surface quenching and energy back transfer from Yb3+ to Er3+, the population density of excited states of Er3+ (4I13/2, 4I11/2 and 4I9/2) was much improved, resulting in the tremendously enhanced upconversion intensity of β-NaErF4:0.005Tm@NaYbF4@NaYF4. This one-pot protocol could supply core–shell–shell red UCNCs with regular morphology, enhanced intensity and long-lasting decay lifetime, offering promising opportunities for applications such as bioprobing, anti-counterfeiting, photodynamic therapy, etc.
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