Li Anming, Xu Dekang, Lin Hao, Yao Lu, Yang Shenghong, Shao Yuanzhi, Zhang Yueli, Chen Zhenqiang
State Key Laboratory of Optoelectronic Materials and Technologies, School of Materials Science and Engineering/School of Physics, Sun Yat-sen University, Guangzhou 510275, China.
Phys Chem Chem Phys. 2017 Jun 21;19(24):15693-15700. doi: 10.1039/c7cp00855d.
We propose a novel and efficient F anion doping strategy for enhancing upconversion luminescence in upconversion nanophosphors. NaGd(MoO):Yb/Er nanophosphors doped with different F contents are synthesized hydrothermally. Rietveld refinement results obtained from X-ray diffraction data indicate that the Gd-O bond length decreases and the O-Gd-O bond angle varies with increasing F content, resulting in augmented local crystal field strength and distorted local site symmetry of the dopant lanthanide sites. Judd-Ofelt analysis suggests that the calculated radiative quantum efficiency of the S level and the radiative branching ratio of S → I transition in F-doped NaGd(MoO):Yb/Er nanophosphors are much greater than those in F anion-free samples. It is inferred that F anion doping helps to reduce the nonradiative transition probabilities based on the luminescence dynamics. Rietveld refinement results and Judd-Ofelt analysis confirm jointly that doping of interstitial F anions could enhance local crystal field strength with odd parity and modify site symmetry of the lanthanide activator ions, leading to enhanced radiative transitions and inhibited nonradiative transitions. A maximum of 17-fold enhancement of total emission intensity is found in NaGd(MoO):Yb/Er/F nanophosphors compared with F anion-free counterparts. The proposed F anion doping strategy provides an alternative approach for enhancing upconversion luminescence efficiency and could be extended to other inorganic upconversion nanomaterials.
我们提出了一种新颖且高效的氟阴离子掺杂策略，用于增强上转换纳米磷光体的上转换发光。通过水热法合成了掺杂不同氟含量的NaGd(MoO)：Yb/Er纳米磷光体。从X射线衍射数据获得的Rietveld精修结果表明，随着氟含量的增加，Gd-O键长减小，O-Gd-O键角发生变化，导致掺杂镧系元素位点的局部晶体场强度增强，局部位点对称性畸变。Judd-Ofelt分析表明，在氟掺杂的NaGd(MoO)：Yb/Er纳米磷光体中，S能级的计算辐射量子效率和S→I跃迁的辐射分支比远大于无氟阴离子样品中的值。基于发光动力学推断，氟阴离子掺杂有助于降低非辐射跃迁概率。Rietveld精修结果和Judd-Ofelt分析共同证实，间隙氟阴离子的掺杂可以增强具有奇宇称的局部晶体场强度，并改变镧系激活离子的位点对称性，从而导致辐射跃迁增强和非辐射跃迁受到抑制。与无氟阴离子的对应物相比，在NaGd(MoO)：Yb/Er/F纳米磷光体中发现总发射强度最大增强了17倍。所提出的氟阴离子掺杂策略为提高上转换发光效率提供了一种替代方法，并且可以扩展到其他无机上转换纳米材料。
