Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang, Liaoning 110819, China.
Dalton Trans. 2018 Jul 3;47(26):8646-8655. doi: 10.1039/c8dt00792f.
Submicron sized, monodispersed spheres of Mn2+, Yb3+/Er3+ and Mn2+/Yb3+/Er3+ doped α-NaYF4 were easily autoclaved from mixed solutions of the component nitrates and ammonium fluoride (NH4F), in the presence of EDTA-2Na. Detailed characterizations of the resultant phosphors were obtained using XRD, Raman spectroscopy, FE-SEM, HR-TEM, STEM, PLE/PL spectroscopy, and fluorescence decay analysis. Finer structure and better crystal perfection was observed at a higher calcination temperature, and the spherical shape and excellent dispersion of the original particles was retained at temperatures up to 600 °C. Under the 980 nm infrared excitation, the Yb3+/Er3+-doped sample (calcined at 400 °C) exhibits a stronger green emission centered at ∼524 nm (2H11/2 → 4I15/2 transition of Er3+) and a weaker red emission centered at ∼657 nm (4F9/2 → 4I15/2 transition of Er3+). A 200 °C increase in the temperature from 400 °C to 600 °C resulted in the dominant red emission originating from the 4F9/2 → 4I15/2 transition of Er3+, instead of the previously dominant green one. Mn2+ doping induced a remarkable more enhanced intensity at ∼657 nm and ∼667 nm (red emission area) than that at ∼524 nm and ∼546 nm (green emission area), because of the non-radiative energy transfer between Mn2+ and Er3+. However, a poor thermal stability was induced by Mn2+ doping. The observed upconversion luminescence of the samples calcined at 400 °C and 600 °C followed the two photon process and the four photon process, respectively.
采用 EDTA-2Na 作为螯合剂，从混合的各组分硝酸盐和氟化铵（NH4F）溶液中，很容易水热釜合成出亚微米级、单分散的 Mn2+、Yb3+/Er3+和 Mn2+/Yb3+/Er3+掺杂的α-NaYF4 纳米球。采用 XRD、拉曼光谱、FE-SEM、HR-TEM、STEM、PLE/PL 光谱和荧光衰减分析对所得荧光粉进行了详细的表征。在较高的煅烧温度下，观察到更精细的结构和更好的晶体完整性，而在高达 600°C 的温度下，原始颗粒的球形形状和优异的分散性得以保留。在 980nm 红外激发下，Yb3+/Er3+掺杂的样品（在 400°C 下煅烧）在 ∼524nm 处（Er3+的 2H11/2→4I15/2 跃迁）显示出更强的绿光发射，在 ∼657nm 处（Er3+的 4F9/2→4I15/2 跃迁）显示出较弱的红光发射。从 400°C 到 600°C，温度升高 200°C，导致主要的红光发射源于 Er3+的 4F9/2→4I15/2 跃迁，而不是之前主要的绿光发射。由于 Mn2+和 Er3+之间的非辐射能量转移，Mn2+掺杂导致在 ∼657nm 和 ∼667nm（红光发射区域）处的强度比在 ∼524nm 和 ∼546nm（绿光发射区域）处显著增强。然而，Mn2+掺杂导致较差的热稳定性。在 400°C 和 600°C 下煅烧的样品的上转换发光分别遵循双光子过程和四光子过程。
