Anomalous Phase Relaxation Characteristics in CuCl Quantum Dots Analogous to That in Dye-Molecules in Polymer

We report on results of a degenerate four-wave-mixing (FWM) experiment in time domain for confined excitons in CuCl spherical dots with average radius of 5.4 nm embedded in a glass matrix. The result observed by 200 fs pulses reveals that at low temperatures the signal shows a single exponential decay for weak excitation power. The phase relaxation time T2 of the exciton is estimated as ≈︂130 ps at 2 K, corresponding to ≈︂10 μeV homogeneous width. At higher temperatures, however, the signal at the leading part changes remarkably in shape, i.e., it becomes prominent, but afterward shows a single exponential decay. This feature resembles very much that in dye-molecules in polymer. A value of T2 becomes shorter as the temperature is raised. The excitation spectrum observed by using picosecond pulses is also presented.