A sandwiched luminescent heterostructure based on lanthanide‐doped Gd₂O₂S@NaYF₄ core/shell nanocrystals

Lanthanide (Ln 3+ ) oxysulfide nanocrystals (NCs) have great prospect in many advanced technologies; however, they suffer from a low photoluminescence efficiency due to the volatility of sulfur and deleterious surface quenching effect. Herein, we report a novel sandwiched luminescent heterostructure based on Ln 3+ ‐doped Gd 2 O 2 S@NaYF 4 core/shell NCs with tunable sulfur content in the sandwich layer. By means of Eu 3+ as the sensitive structural probes, we unravel the ligand‐mediated structure control of the NCs from Gd 2 O 3 : Ln 3+ @NaYF 4 to Gd 2 O 2 S: Ln 3+ @NaYF 4 with tailored S 2– deficiency. Such a sandwich‐type core/shell heterostructure enables us to achieve efficient and multicolor downshifting and upconversion luminescence (UCL), with up to 208.8 folds of enhancement in UCL intensity as compared to that of their core‐only counterparts. These findings provide a general approach for the controlled synthesis of lanthanide oxysulfide@fluoride heterostructure, which offers a new way for the materials design towards diverse emerging applications.