Single-Particle Photoluminescence Spectra, Blinking, and Delayed Luminescence of Colloidal CuInS₂ Nanocrystals

Single-nanocrystal and ensemble photoluminescence measurements on CuInS₂ semiconductor nanocrystals reveal luminescence bandshapes that are broad compared to those typical of individual II–VI or related semiconductor nanocrystals. This finding is consistent with the hypothesis of strong electron–phonon coupling in the emissive excited state of these CuInS₂ semiconductor nanocrystals. Blinking is observed that resembles that of other semiconductor nanocrystals. Ensemble luminescence measurements also reveal the existence of a remarkably long-lived excited state in these nanocrystals that continues to emit photons over several orders of magnitude in time following the excitation pulse. The delayed luminescence overlaps in time and shows similar distributed kinetics to the blinking “off” times of the same nanocrystal sample, supporting the proposal that these two phenomena arise from the same microscopic carrier-trapping and -detrapping processes. Excitation power dependence measurements illustrate that the delayed luminescence saturates at very low emission intensities under the excitation power densities used in the single-nanocrystal measurements, consistent with this metastable charge-trapped state being the “off” state of the luminescence blinking cycle