Picosecond defect formation by optical conversion from self-trapped excitons in alkali halide crystals

Abstract

The optical conversion from metastable self-trapped excitons at the lowest triplet state (STE L) to F centers in NaCl single crystals has been observed in picosecond range with time-delayed double excitation spectroscopy. The absorption due to STE L's induced by the first excitation with a KrF laser was instantaneously bleached under the second excitation with a mode-locked ruby laser, while the absorption due to F centers increased within the pulse duration (40ps) of the ruby laser. The excitation power dependence of the secondarily induced F absorption intensity suggests that the conversion from STE L to F center occurs faster than 2 ps with an efficiency less than 8%.