A general strategy via charge transfer sensitization to achieve efficient NIR luminescence in lanthanide-doped NaGdS2 nanocrystals

Lanthanide (Ln3+)-doped near-infrared (NIR) luminescent nanocrystals (NCs) have shown great promise in many technological fields. However, because of the parity-forbidden 4f → 4f electronic transitions of Ln3+, these NCs normally suffer from a low absorption and luminescence efficiency. Herein, we report a novel strategy for sensitizing the NIR luminescence of Ln3+ in NaGdS2 NCs based on the ligand-to-metal charge transfer transition from S2− to Yb3+. Through sensitization by the allowed S2−–Yb3+ charge transfer transition, intense NIR luminescence from Yb3+ and Er3+ with quantum yields up to 21.2% and 25.0% is achieved in Yb3+ singly-doped and Yb3+/Er3+ co-doped NaGdS2 NCs, respectively. These findings provide a general approach for the development of highly efficient Ln3+-doped NIR luminescent NCs through charge transfer sensitization, and also lay a foundation for future design of sulfide-based NIR luminescent nanomaterials towards various applications.