Quantum-size effects on the exciton excited states of CuCl nanocrystals

We have investigated infrared transient absorption at 77 K, which appears under size-selective excitation of 1S excitons in CuCl nanocrystals err bedded in NaCl matrices. The transient absorption is mainly ascribed to the optical transition between the 1S to 2P exciton states in CuCl nanocrystals. The peak energy of the transient absorption band increases by about 200 meV with the decrease in the crystal size from more than 10 nm down to 1.4 nm in effective radii, while the width of the band increases by more than 100 meV. These facts indicate that the quantum size effect on the exciton excited state is much deviated from the exciton confinement regime and the hydrogen-like P exciton components are widely distributed among the various excited confinement states split by the quantum size effect.