Infrared transient absorption and excited-states of excitons and biexcitons confined in CuCl quantum dots

Mid-infrared picosecond transient absorption has revealed a new aspect of the excited states of confined biexcitons in CuCl quantum dots embedded in a NaCl matrix. The transient absorption exhibits two-decay components that originate from confined excitons and biexcitons. The attribution of the fast-decay component to the confined biexcitons has been confirmed by measurement by a two-photon resonant excitation process. The transient-absorption spectrum of biexcitons indicates the existence of a stable biexciton excited state in the quantum dots, in contrast to the unstable excited state in the bulk crystal.