Abstract
Luminescence spectra of excitons localized at iodine or bromine ions in CsCl have been studied in the temperature range 10--300 K. Two bands appear at 3.96 and 5.13 eV in CsCl:I, while three bands are observed at 3.84, 4.34 and 5.27 eV in CsCl:Br. The decay behaviors of these bands are measured under the single-bunch operation of synchrotron radiation. It is found that the 4.34-eV luminescence in CsCl:Br has a rise component around 1 ns just after the pulse excitation. In addition, time-resolved luminescence spectra are investigated through two different time windows. For the 3.96-eV luminescence in CsCl:I, the slow-component peak is located about 40 meV lower than the fast-component peak. For the 4.34-eV luminescence in CsCl:Br, the slow-component peak is located 210 meV lower than the fast one. These results suggest that an adiabatic potential energy surface has some local minima for the localized excitons in CsCl. The difference in the relaxation process of excitons between NaCl- and CsCl-type structures is discussed.
