Energy transfer from self-trapped excitons in NaCl to physisorbed C 2H 2

Abstract

Here we explore self-trapped excitons (STEs) in NaCl crystallites that are roughly cubic and ≈ 100 nm on a side. Following excitation of the crystallites at 150 K with 192 nm laser pulses, luminescence in the UV and visible is observed. Based on the wavelength similarities and lifetime decay characteristics of this luminescence with previous studies with large, high purity single crystals of NaCl, we assign the sources of these emissions as the 1∑ + u and 3∑ + u STE states. On adsorption of C 2H 2 to the surface of these crystallites the triplet STE emission is quenched but the singlet emission is not. We propose an energy transfer from the triplet STE to a near-resonant excited triplet state of C 2H 2. Our study shows that energy stored in the metastable (triplet) STE of NaCl can be efficiently transferred to a surface bound molecule.