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Subpicosecond Spectroscopy of CuCl Nanocrystals in NaCl

In CuCl nanocrystals, we observed the nonlinear change in the exciton absorption spectra and the appearance of the structures (gain and loss) near the energy region of biexciton luminescence band using the subpicosecond pump-and-probe method under high intensity excitation at 2K and 77K. We observed the decay time of the exciton absorption change at 2K to be about 1ns, twice as large as that at 77K. We found out that the peak positions of the gain and the loss differed in energy at 2K, while they had the same energy at 77K. Taking into account of the luminescence and their time behavior, we got the evidence that the transitions from the biexciton state to “bound” and “free” exciton states occur simultaneously at 2K.