Local Cluster Distortions in Amorphous Organotin Sulfide Compounds and Their Influence on the Nonlinear Optical Properties

The local structure of four amorphous organotin sulfide compounds is investigated by X-ray absorption spectroscopy. These compounds exhibit a nonlinear optical (NLO) response upon irradiation with a continuous-wave near-infrared laser. Their basic structural motif is a hetero-adamantane cluster with different organic substituent, but depending on the morphology of the compound and the choice of the organic substituent, the nature of the NLO response changes to either a second harmonic generation or the generation of a supercontinuum, potentially appearing as white light. The structural results provide an experimental evidence that the nature of the NLO properties is tied to distortions occurring at the cluster core, with almost ideal clusters in compounds that show second harmonic generation, and strongly distorted clusters in the case of compounds that generate a supercontinuum. These distortions may enable a closer proximity of the cluster cores, altering the intermolecular order, and thereby influencing the NLO response.