Electrogenerated chemiluminescence (ECL) was observed from TOPO-capped CdSe nanocrystals dissolved in CH 2 Cl 2 containing 0.1 M TBAP. The solution of monodisperse nanocrystals with an absorption maximum at 537 nm was synthesized at 330 °C using TOPO (trioctylphosphineoxide) and TOP (trioctylphosphine) as capping agents and Cd-acetate and Se powder as precursors. The photoluminescence (PL) spectrum showed an emission maximum at 545 nm. Cyclic voltammetry and differential pulse voltammetry of this solution displayed no distinctive features, but light emission was observed through the annihilation of oxidized and reduced forms electrogenerated during cyclic potential scans or steps. The oxidized species was somewhat more stable than the reduced form. The ECL spectrum was substantially red shifted by ∼200 nm from the PL spectrum, suggesting that surface states play an important role in the emission process.

Differential pulse voltammetry (DPV) of TOPO-capped CdTe nanoparticles (NPs) in dichloromethane and a mixture of benzene and acetonitrile showed two anodic and one cathodic peaks of the NPs themselves and an additional anodic peak resulting from the oxidation of reduced NPs. The electrochemical band gap (∼2.1 eV) between the first anodic and cathodic DPV peaks was close to the value (2 eV) obtained from the absorption spectrum. Electrogenerated chemiluminescence (ECL) of CdTe NPs was highly intense for scans into the negative potential region in dichloromethane. The fact that the ECL peak occurs at about the same wavelength as the band-edge photoluminescence (PL) peak indicates that, in contrast to CdSe NPs, the CdTe NPs as synthesized had no deep surface traps that can cause a substantially red shifted ECL.

The electrogenerated chemiluminescence (ECL) spectrum of CdSe/ZnSe nanocrystals (NCs) dispersed in a CH2Cl2 solution containing 0.1 M TBAP was obtained by stepping the potential between +2.3 and −2.3 V. Unlike the spectra from the ECL of Si or CdSe NCs, where the emission occurs in a single peak that is significantly red-shifted from the photoluminescence (PL) peak (attributed to emission from surface states), ECL from CdSe/ZnSe produced a spectrum containing two peaks:  a sharp peak whose position was almost identical to that in the PL spectrum and another broader peak with a red shift of ∼200 nm compared to that in the PL. This suggests emission from both surface states on the NCs and from the bulk in NCs where the surface states have been passivated.