Lanthanide (Ln³⁺)-doped oxysulfide nanocrystals (NCs) are interesting for different fields of research due to their useful optical properties. However, it can be challenging to synthesize monodisperse lanthanide oxysulfide NCs with high luminescence efficiency. This is due to the volatility of sulfur and a surface quenching effect, and it limits the application of lanthanide oxysulfide NCs.

Wei Zheng, Ping Huang, Xueyuan Chen, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, China, and colleagues have prepared a new sandwich-type luminescent heterostructure based on Ln³⁺-doped Gd₂O₂S@NaYF₄ core/shell NCs with tunable sulfur content in the sandwich layer. The desired structures were prepared via epitaxial growth of α-NaYF₄ on Ln³⁺-doped Gd₂O₂S NCs (Ln Eu, Tb, Dy, Sm, Yb, Er, Tm, Ho). The researchers found that varying the ratio of the ligands oleylamine and oleic acid during the synthesis allowed them to tailor the S^2– deficiency in the sandwich layer.

Using different dopants, the team achieved multicolor upconversion and downshifting luminescence under single-wavelength excitation at 980 and 254 nm, respectively, with remarkably improved intensities compared with those of the doped Gd₂O₂S core. Thus, the work provides a general approach for boosting the luminescence efficiency of lanthanide oxysulfide NCs via heterostructured core/shell engineering and could open up new opportunities for the design of advanced materials for applications such as multimodal bioimaging, nanoscintillators, and photocatalysis.

• A sandwiched luminescent heterostructure based on lanthanide‐doped Gd₂O₂S@NaYF₄ core/shell nanocrystals,
  Dengfeng Yang, Wei Zheng, Ping Huang, Meiran Zhang, Wei Zhang, Zhiqing Shao, Wen Zhang, Xiaodong Yi, Xueyuan Chen,
  Aggregate 2023.
  https://doi.org/10.1002/agt2.387