Three types of emission bands from hetero-nuclear relaxed excitons in NaBr:I, KBr:I and RbBr:I

Luminescence from hetero-nuclear relaxed excitons, [(BrI)^-+e], has been studied under steady or pulsed UV-light excitation into the localized exciton absorption due to I^- impurities in NaBr, KBr and RbBr. One, two and three emission bands were found in the respective matrices. A prominent emission band is located at 4.6 eV in NaBr:I, at 3.5 eV in KBr:I or at 2.5 eV in RbBr:I, having a largely different lifetime of 230 ns, 3.3 μs or 19 μs, respectively. Variations in the peak position and the lifetime of these three bands are very similar to those of intrinsic π emission bands from the self-trapped excitions (STE), [I^-₂ + e], in pure NaI, KI and RbI. Existence of three locally stable configurations responsible for emission bands is discussed in connection with the off-center shift of the V_K core in the STE.