Intrinsic Luminescence in KBr Crystals between 1.8 K and 80 K

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Intrinsic luminescence and optical absorption from the triplet state of the self trapped exciton in KBr crystals have been observed by a pulsed electron beam and by a N₂ laser. The π emission at 2.28 eV decays with two components of ∼3 ms(τ_S) and 100 μs(τ_F) at 1.8 K. τ_F component arises from a transition from B_u (a combined state of B_3u and B_2u) to A_g, and τ_S component from A_u→B_u→A_g in the self trapped exciton as those in KI reported by Fischbach et al. The energy separation between B_u and A_u is 1.6 meV. In addition to the above, temperature dependence of the yield of the 2.28 eV emission and of the self trapped excitons at the triplet state is discussed in connection with the F center formation.