Solvent polarity-induced photoluminescence enhancement (SPIPE): A method enables several-fold increase in quantum yield of silicon nanoparticles

Fluorescent silicon nanoparticles (SiNPs) bring exciting opportunities for long-awaited silicon-based optical application, while intrinsic indirect band gap of silicon severely limits photoluminescent quantum yield (PLQY) of SiNPs. To address this critical issue, we herein demonstrate a facile and general method, i.e., solvent polarity-induced photoluminescence enhancement (SPIPE), yielding several-fold increase in quantum yield (QY) of SiNPs. Typically, different kinds of 4-substituented-1,8-naphthalic anhydride molecules, i.e., 4-Br-1,8-naphthalic anhydride (BNA), 4-triphenylamino-1,8-naphthalic anhydride (TPNA), and 4-dimethylamino-1,8-naphthalic anhydride (DMNA), are rationally designed and synthesized, which serve as surface ligands for the production of BNA-, TPNA-, and DMNA-capped small-sized (diameter: ~ 3.8–5.8 nm) SiNPs with QY of ~ 8%, ~ 15%, ~ 16%, respectively. Of particular significance, QY of the resultant SiNPs could be greatly enhanced from ~ 10% to ~ 50% through the SPIPE strategy. Taken together with the theoretical calculation and the results of time-correlated single photon counting, we reveal that actived excited-state charge transfer interactions between surface-covered ligand and silicon oxide coating would be responsible for the observed QY enhancement. Moreover, other five kinds of solvents (i.e., methanol, isopropanol, dimethyl sulfoxide, N, N-dimethylformamide, and acetonitrile) are further employed for the SiNPs treatment, and similar improvement of QY values are observed, convincingly demonstrating the universal evidence of SPIPE of the SiNPs.