Picosecond recombination dynamics of electrons in ionic liquids

Abstract

We report picosecond transient optical-absorption decays for electrons localized in F-center analogues in molten KCl and KBr. Absorption decays were recorded for 750 ps after electron-hole generation by a 266-nm ultraviolet pulse. The recombination process is analyzed in terms of reactions involving the anionic hole centers ${\mathrm{X}}_2^{\mathrm{-}}$ and ${\mathrm{X}}_3^{\mathrm{-}}$ where X+Cl or Br. The results confirm by direct real-time measurement that F-center electrons are sufficiently mobile to account for the electronic conductivity observed in dilute metal-molten salt solutions. This demonstrates the necessary presence of a new polaronlike transport mechanism involving diffusive modes of ionic motion.