Photoinduced infrared absorption spectra of CuCl quantum dots in NaCl

We have studied infrared transient absorption spectra of CuCl QDs grown inside a NaCl matrix under tunable UV laser excitation on resonance with the confined excitons. In addition to the transient excited-state absorption, there appears induced IR absorption with lifetime much longer than that of the confined exciton. The peak energy remains at ~0.3 eV regardless of the QD size. The optical density is proportional to the square root of the UV laser power. The decay of the induced absorption is logarithmic on time and is accelerated by the irradiation of light below the band gap. We assign this absorption to be originated from the electron-bound defect center called I_e center generated in the NaCl side of the interface and discuss it phenomenon in relation with photo-irradiation effects, such as photofatigue, blinking of the luminescence and hole burning.