Persistent spectral-hole-burning spectroscopy of CuCl quantum cubes

A persistent spectral-hole-burning (PSHB) phenomenon was successfully applied to the precise site-selective spectroscopy of CuCl quantum dots embedded in NaCl crystals. In the PSHB spectra of CuCl quantum dots, a resonantly burned hole and lower-energy satellite holes were observed. These satellite holes are supposed to originate from hole burning of the ground states, which results from site-selective excitation of the corresponding excited states of excitons confined in CuCl quantum dots. Energy relation between the resonantly burned hole and each satellite hole is well explained by the simple concept of a particle in a quantum cube with an infinitely high potential barrier. However, actual quantum dots are considered to be a little deviated from cubes, resulting in the violation of the optical selection rule in quantum cubes. A cubic-shaped quantum-dot model is almost consistent with oscillatory fine structures observed in the $Z_3$ exciton absorption band. Its spectral decomposition into the ground state and the first excited state of excitons was made, and showed that the first excited state is in majority at the higher-energy region of the $Z_3$ exciton absorption band. This result was supported by the photoluminescence spectrum of the $Z_3$ exciton.