Multicolor Band-Edge Electrochemiluminescence of Colloidal Silicon Quantum Dots in a Thin-Layer Cell

We demonstrate band-edge, multicolor, electrochemiluminescence (ECL) of colloidal silicon quantum dots (SiQDs) in a thin-layer transparent two-electrode cell configuration. SiQDs with different size distributions are prepared by low-temperature thermal cracking of porous silicon and subsequent size separation using the gel permeation chromatography technique. The cell consisting of an organic solution-dispersed SiQD layer between two thin transparent electrodes exhibits orange to red luminescence at a voltage of ∼3 V depending on the size distribution of SiQDs. The electrochemical analysis of SiQDs by the cyclic voltammetry technique and theoretical calculations confirm the formation of an electric double layer, revealing that electron–hole pair excitation in SiQD cores occurs in association with collisions between electrically generated cations and anions of SiQDs at the transparent electrodes of the cell. Radiative recombination of excited electron–hole pairs at the band-edges of the size-dependent electronic energy gap of the SiQDs enables the multicolor ECL from the cell.