Persistent spectral hole burning in semiconductor nanocrystals

A persistent spectral hole-burning phenomenon in nanometer-size semiconductor microcrystals (nanocrystals), namely, CdSe, CdS0.59Se0.41, and CuCl, embedded in a crystal or glass was observed. When the spectrally narrow laser excites the inhomogeneously broadened absorption band of CdSe and CuCl nanocrystals, a narrow bleaching hole and induced absorption arise in the absorption spectra at 2 K and are present for more than a few hours after the laser irradiation. Long-lived bleaching was observed also in CdS0.59Se0.41 nanocrystals together with photodarkening. A photophysical model explains the long-lived bleaching ascribed to the spectral antihole fairly well, but some part of the persistent spectral hole burning comes from the photochemical mechanism. Nanocrystals consisting of 103–104 atoms behave like molecules or ions in a matrix to give the persistent spectral hole-burning phenomenon. This means that the total system consisting of even one semiconductor nanocrystal and the matrix has more than one ground-state configuration. Not only the size distribution but also these ground-state configurations give inhomogeneous broadening to semiconductor nanocrystals