Evolution from individual to collective electron states in a dense quantumdot ensemble

Absorption spectrum of a quantum dot ensemble was found to exhibit a system atic modification with dot concentration from a set of discrete subbands in herent in isolated nanocrystals to a smooth band-edge absorption similar to that of bulk semiconductors. The results are interpreted in terms of an ev olution from individual (localized) to collective electron states delocaliz ed within at least a finite number of nanocrystals. The observed behavior i s considered as a possible precursor of the Anderson transition in a quantu m dot ensemble, i.e., a transition from localized electron states to states that are delocalized over a macroscopically large number of nanocrystals. [S0163-1829(99)01327-2].