Thermal decomposition of the molecular single-source precursor (PPh3)(2)CuIn(SEt)(4) in the presence of hexanethiol in dioctylphthalate forms colloidal CuInS2 at 200 degreesC. The colloidal solution displays size-dependent quantum confinement behavior in the absorption and photoluminescence spectra. The average size of the nanocrystals can be increased from 2 to 4 nm by raising the reaction temperature from 200 degreesC to 250 degreesC. The nanoparticles are capped with hexanethiol ligands; these ligands can be exchanged with trioctylphosphine oxide or pyridine. The nature of the surface-capping ligands has a significant effect on the photoluminescence emission intensity. Investigation of the effect of synthesis parameters and postsynthesis treatments on the optical properties of the nanocrystals leads to the conclusion that the room-temperature emission originates in donor-acceptor defects.