Photoinduced Electrochemiluminescence at Silicon Electrodes in Water

We introduce the photoinduced electrochemiluminescence (P-ECL) of the model ECL system involving the simultaneous oxidation of [Ru(bpy)₃]²⁺ and tri-n-propylamine (TPrA). This system classically requires highly anodic potentials of greater than +1 V vs SCE for ECL generation. In the reported approach, the ECL emission is triggered by holes (h⁺) photogenerated in an n-type semiconductor (SC) electrode, which is normally highly challenging because of competing photocorrosion occurring on SC electrodes in aqueous electrolytes. We employ here Si-based tunnel electrodes protected by few-nanometer-thick SiO and Ni stabilizing thin films and demonstrate that this construct allows generation of P-ECL in water. This system is based on an upconversion process where light absorption at 810 nm induces ECL emission (635 nm) at a record low electrochemical potential of 0.5 V vs SCE. Neither this excitation wavelength nor this low applied potential is able to stimulate ECL light if applied alone, but their synergetic action leads to stable and intense ECL emission in water. This P-ECL strategy can be extended to other luminophores and is promising for ultrasensitive detection and light-addressable and imaging devices.