Vibronic Structures in Excitation and Emission Spectra Characteristics of O2- Molecular Ions in KI, KBr and KCl Crystals

Abstract

The excitation and emission spectra of O2- molecular ions in KI, KBr and KCl crystals have systematically been investigated at 8.7 K. The present results for the emission spectra with zero-phonon lines were in good agreement with previous results. From the temperature dependence of their emissions, we found that the luminescence intensities of O2- ions still appear at room temperature (RT) and are much stronger than those of other chalcogen molecular ions particularly in a KCl crystal. On the other hand, we found vibronic structures on the low-energy sides of the excitation spectra of KI and KBr:O2- crystals, showing several peaks with nearly equidistant spacings. The anharmonic vibrational energies of O2- molecular ions in the excited state were obtained from these energy differences, depending on their lattice constants. Using spectroscopic constants calculated from the experimental data, we could construct a configurational-coordinate diagram for an O2- center in a KI:O2- crystal.