Lanthanide (Ln)-doped nanoparticles have shown potential for applications in various fields. However, the weak and narrow absorption bands of the Ln ions (${\mathrm{Ln}}^{3+}$), hamper efficient optical pumping and severely limit the emission intensity. Dye sensitization is a promising way to boost the near-infrared (NIR) emission of ${\mathrm{Er}}^{3+}$, hence promoting possible application in optical amplification at 1.5 μm, a region that is much sought after for telecommunication technology. Herein, we introduce the fluorescein isothiocyanate (FITC) organic dye with large absorption cross section as energy donor of small-sized ($\sim 3.6\mathrm{nm}$) ${\mathrm{Er}}^{3+}$-doped ${\mathrm{CaF}}_2$ nanoparticles. FITC molecules on the surface of ${\mathrm{CaF}}_2$ work as antennas to efficiently absorb light, and provide the indirect sensitization of ${\mathrm{Er}}^{3+}$ boosting its emission. In this paper, we employ photoluminescence and transient absorption spectroscopy, as well as density functional theory calculations, to provide an in-depth investigation of the $\mathrm{FITC}\to {\mathrm{Er}}^{3+}$ energy transfer process. We show that an energy transfer efficiency of over 89% is achieved in ${\mathrm{CaF}}_2\text{:}{\mathrm{Er}}^{3+}@\mathrm{FITC}$ nanoparticles resulting in a 28 times enhancement of the ${\mathrm{Er}}^{3+}$ NIR emission with respect to bare ${\mathrm{CaF}}_2\text{:}{\mathrm{Er}}^{3+}$. Through the multidisciplinary approach used in our work, we are able to show that the reason for such high sensitization efficiency stems from the suitable size and geometry of the FITC dye with a localized transition dipole moment at a short distance from the surface of the nanoparticle.

中文翻译：

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染料敏化 Er3+ 掺杂的 CaF2 纳米粒子可增强 1.5 μm 的近红外发射

镧系元素 (Ln) 掺杂的纳米粒子已显示出在各个领域的应用潜力。然而，Ln 离子的弱吸收带和窄吸收带（${\mathrm{LN}}^{3+}$)，阻碍了有效的光泵浦并严重限制了发射强度。染料敏化是一种提高近红外 (NIR) 发射的有前途的方法${尔}^{3+}$，因此促进了 1.5 μm 光放大的可能应用，这是电信技术备受追捧的领域。在此，我们介绍了具有大吸收截面的异硫氰酸荧光素（FITC）有机染料作为小尺寸（$～3.6\mathrm{纳米}$) ${尔}^{3+}$-掺杂 ${\mathrm{氟化钙}}_2$纳米粒子。表面的 FITC 分子${\mathrm{氟化钙}}_2$ 作为天线有效地吸收光，并提供间接敏化 ${尔}^{3+}$提高其排放量。在本文中，我们采用光致发光和瞬态吸收光谱以及密度泛函理论计算，对$\mathrm{国际贸易委员会}\to {尔}^{3+}$能量转移过程。我们表明，在以下情况下实现了超过 89% 的能量传输效率${\mathrm{氟化钙}}_2\text{：}{尔}^{3+}@\mathrm{国际贸易委员会}$ 纳米粒子导致 28 倍的增强 ${尔}^{3+}$ 相对于裸露的 NIR 发射 ${\mathrm{氟化钙}}_2\text{：}{尔}^{3+}$. 通过我们工作中使用的多学科方法，我们能够证明如此高的敏化效率的原因源于 FITC 染料的合适尺寸和几何形状，在距纳米颗粒表面很短的距离处具有局部跃迁偶极矩。