Photo‐Induced Transformation of Close Frenkel Pairs in Strontium Fluorite

Laser‐induced change is studied of the optical absorption and luminescence due to F‐H pairs generated by an electron pulse in SrF2. It is found that laser irradiation near 2.34 eV at a delay of 26 μs after an electron pulse by which F‐H pairs are generated reduces the component I of the pairs that has a decay time of 59 μs and optical absorption bands at 2.34 and 4.13 eV and enhances the component II that has a decay time of 7.7 ms and has optical absorption bands at 2.7 and 3.35 eV. Laser irradiation near 2.7 eV at a delay of 4 ms after the electron pulse is found to induce the reverse reaction. Studies of dichroism of the laser‐induced reduction and enhancement of the optical absorption bands and the luminescence reveal that the direction of the Σ‐Σ transition of the F molecular ion is converted by the transformation from I to II and vice versa. It is suggested that the component I corresponds to the F‐H pairs at nearest‐neighbour and II to those at the next‐nearest neighbour sites.