Facile synthesis of silicon quantum dots with photoluminescence in the near-ultraviolet to violet region via wet oxidation†

Abstract

To extend the photoluminescence (PL) of silicon quantum dots (SiQDs) into the near-ultraviolet–violet (NUVV) region, the size of SiQDs must be reduced to less than 1.53 nm. However, this significantly increases both the difficulty and the cost of synthesis. Herein, we report a facile wet oxidation treatment to obtain SiQDs with PL emission in the NUVV region while elucidating their emission mechanism. The synthesized SiQDs exhibit an average diameter of 4.95 nm, with F-band emission peaks ranging from 332 to 420 nm, which are blue-shifted by approximately 500 nm compared to the near-infrared (NIR) counterparts lacking wet oxidation treatment. Notably, the synthesized SiQDs achieve an average photoluminescence quantum yield (PLQY) of 19.05%, a 6.24-fold increase over their NIR counterparts. Comprehensive examinations attribute this NUVV emission to two types of oxygen defects: peroxy linkage (POL) and oxygen-deficient center (ODC(I)). Under wet oxidation conditions, SiO_x networks containing these oxygen defects, rather than simple Si–O–Si groups, are formed on the surface of SiQDs. Furthermore, after storing the SiQDs in ambient air for approximately two months, no intrinsic or additional defect-induced emissions were observed, and 88% of the initial PLQY was retained, indicating favorable stability of the SiQDs. This study provides valuable insights into oxygen-related defect-induced emission mechanisms on SiQD surfaces.