Luminescence properties of KCl:Ag− crystals excited near the fundamental absorption edge

Luminescence properties of KCl single crystals doped with Ag− centers have been investigated under various excitation energies around the fundamental absorption edge at low temperatures. Under the excitation at 6.89 eV, which is lower than the intrinsic exciton energy by 0.87 eV, the image luminescence band due to the intraionic transition in the Ag− ion is dominantly observed at 2.91 eV. On the other hand, the excitation at 6.66 eV induces a broad luminescence band at 2.60 eV in addition to the image luminescence band. From the comparison with the localized excitons in KCl:I crystals, the 2.60 eV luminescence band is attributed to the two-center type localized exciton related with the Ag− ion. The adiabatic potential energy surfaces of the excited states in the Ag− center and the localized exciton in KCl:Ag− are discussed.