Strong Electrochemiluminescence of Metal Indium Nanoparticles (InNPs) by Surface State Engineering

For the first time, we developed a new type of electrochemiluminescence (ECL) nanomaterial based on zero-band-gap metal nanoparticles (MNPs) by surface state engineering. Herein, we selected indium nanoparticles (InNPs) with a particle size of around 100 nm as the model MNPs and engineered In-O surface states (i.e., InO_x) on the InNPs by treating with O₂ under ultrasonication. The surface states of the treated InNPs were investigated in detail by TEM, XRD, XPS, and UV-vis, indicating that a layer of InO_x shell, consisting of In₂O, InO, and In₂O₃ components, can be engineered on the InNP core. The obtained InNPs@InO_x nanostructures give strong cathodic ECL emission with a broad spectrum over 400-1000 nm and a maximum emission wavelength at 670 nm. It is the first time that MNPs have been found to have ECL activity. The strong and broad-spectrum ECL of InNPs@InO_x has been revealed to result from the abundant InO_x (In₂O, InO, and In₂O₃) surface states on the InNPs with excellent electroconductivity. The engineering of the strongly ECL-active InNPs not only enables us to have a deeper insight into the surface-state-based ECL mechanisms of nanomaterials but also will stimulate the study and application of MNPs-based ECL nanomaterials.