Rare-earth doped upconversion nanoparticles (UCNPs) have attracted wide-ranging interest due to their potential applications in bioimaging and biolabeling, where a high emission intensity and small particle size are needed. However, common synthesis processes can be somewhat complex or require additional reactants, and the use of small-size NPs is limited by their weak luminescence intensity. In this work, uniform, monodisperse ∼5 nm β-NaGdF₄:20% Yb/2% Er NPs were synthesized via a simple one-pot synthesis method in the high boiling-point solvents 1-octadecene (ODE) and oleic acid (OA) using a single dose of NaF at an ultralow NaF concentration of NaF/RE = 4. The effects of NaF/RE, the reaction temperature, and the reaction time on the size and phase of the particles were investigated. High-quality β-NaGdF₄:20% Yb/2% Er@β-NaGdF₄:20% Yb/10% Nd core–shell NPs with a size of ∼13 nm, enhanced UC luminescence, long UC lifetimes (τ) for green (τ ≈ 150 μs) and red (τ ≈ 105 μs) emission under 980 and 808 nm excitation, revealed via lifetime imaging, and obvious emission in the near-infrared (NIR) II region were synthesized. The synthesized core–shell NPs may result in a decrease in the overheating effect and allow for a deep penetration depth when further used for bioimaging applications. This work could inspire the synthesis of other high-quality RE-doped UCNPs via adding a single dose of a small amount of NaF and could lay the foundation for the use of Gd-based UCNPs in biomedical applications.

中文翻译：

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具有NIR-II发射和5 nm核的双模激发β-NaGdF4：Yb / Er @β-NaGdF4：Yb / Nd核-壳纳米粒子：通过NaF / RE调控和生长机理的受控合成

稀土掺杂上转换纳米粒子（UCNPs）由于其在生物成像和生物标记中的潜在应用而引起了广泛的关注，其中需要高发射强度和小粒径。然而，普通的合成过程可能有些复杂或需要其他反应物，而小尺寸NP的使用受到其弱发光强度的限制。在这项工作中，均匀，单分散纳米〜5β-NaGdF ₄：20％的Yb / 2％的NP尔合成通过高沸点溶剂1-十八碳烯（ODE）和油酸（OA）中的简单一锅合成方法，使用单剂量NaF，NaF / RE = 4的超低NaF浓度。NaF/ RE的作用考察了反应温度，反应时间对颗粒尺寸和相的影响。高品质的β-NaGdF ₄：20％的Yb / 2％二@β-NaGdF ₄：20％的Yb / 10％的Nd的芯-壳纳米粒子的大小为〜13纳米，增强UC发光，长寿命UC（τ）通过980和808 nm激发下的绿色（τ≈150μs）和红色（τ≈105μs）发射，通过寿命成像，并合成了近红外（NIR）II区域中的明显发射。当进一步用于生物成像应用时，合成的核壳NP可能会导致过热效果降低，并允许较深的穿透深度。这项工作可以通过添加单剂量的少量NaF来激发其他高质量的RE掺杂UCNP的合成，并且可以为基于Gd的UCNP在生物医学应用中的使用奠定基础。