Pure hexagonal β-NaGdF4 and Eu3+ or Pr3+-doped β-NaGdF4 nanocrystals in shape of nanorods of ∼140 nm of length have been synthesized using a simple and rapid coprecipitation method. XRD analysis evidenced pure single phases exhibiting characteristic luminescence of Eu3+ or Pr3+ ions when excited under UV or blue radiations. Samples gave rise to intense orange-red emission and quite white emission in the case of respectively Eu3+ or Pr3+ doped samples. Optical properties are discussed in the frame of Judd-Ofelt theory and considering that an energy transfer occurs between active ions. Notably it was found that the quantum-cutting by a two-step energy transfer from Gd3+ to Eu3+ can improve the red emission of Eu3+ ions under near-VUV excitation. Such quantum-cutting mechanism has been also considered in the case of Pr3+ doped β-NaGdF4. However, the efficiency of both processes in comparison with literature suggest that only one part of the energy in the excited states within Gd3+ can be transferred to Eu3+ for its red emission. In the case of Pr3+ ions, the energy is more probably released through the self-trapped exciton emission certainly due to the lack of resonant VUV excitation.

中文翻译：

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通过快速共沉淀法获得的 Eu3+ 或 Pr3+ 掺杂的 β-NaGdF4 纳米棒的 Judd-Ofelt 和量子切割分析

使用简单快速的共沉淀方法合成了长度约为 140 nm 的纳米棒形状的纯六方 β-NaGdF4 和 Eu3+ 或 Pr3+ 掺杂的 β-NaGdF4 纳米晶体。XRD 分析证明纯单相在紫外线或蓝色辐射下激发时表现出 Eu3+ 或 Pr3+ 离子的特征发光。在分别掺杂 Eu3+ 或 Pr3+ 的样品的情况下，样品产生强烈的橙红色发射和相当白的发射。在 Judd-Ofelt 理论的框架内讨论了光学特性，并考虑了活性离子之间发生的能量转移。值得注意的是，发现通过从 Gd3+ 到 Eu3+ 的两步能量转移进行的量子切割可以改善近 VUV 激发下 Eu3+ 离子的红色发射。在 Pr3+ 掺杂的 β-NaGdF4 的情况下也考虑了这种量子切割机制。然而，与文献相比，这两种过程的效率表明，在 Gd3+ 中，只有一部分处于激发态的能量可以转移到 Eu3+ 以进行红色发射。在 Pr3+ 离子的情况下，由于缺乏共振 VUV 激发，能量更有可能通过自陷激子发射释放。