Frenkel Defect Formation and Intersystem Crossing at Highly-Excited States of the Triplet Self-Trapped Exciton in NaCl

Measurements were made of the absorption change at the F band and of the singlet luminescence in NaCl, induced by photoexcitation of the lowest state of the triplet self-trapped excitons into excited states higher than the lowest state by 1.7 eV ∼2.8 eV. It is found that excitation with photons below 2.5 eV causes both the F -center creation and the σ-luminescence, while excitation with photons above 2.5 eV causes only the σ-luminescence. These results indicate that non-radiative transition from the higher excited states to the lowest state of the self-trapped exciton is selective. The cause of the selectiveness is discussed. The yield of the F center creation at the higher excited state of the self-trapped exciton was found to be about 10 -2 . The stability of the created F centers in NaCl is found to be lower than in other alkali chlorides.