Structure Determination in a new Type of Amorphous Molecular Solids with Different Nonlinear Optical Properties: A Comparative Structural Analysis

The microscopic structure of two amorphous materials with extreme nonlinear optical properties has been studied. One of these materials exhibits second harmonic generation, while another material of similar molecular structure emits brilliant white light if being irradiated with a simple IR laser diode. Structural differences were investigated using X-ray scattering and EXAFS combined with molecular RMC. Transmission electron microscopy and scanning precession electron diffraction were used to understand specific structural differences on all length scales, from mesoscopic down to mutual molecular arrangements. Characteristic differences were found at all scales. Close core-core spacing between {SnS} clusters as well as characteristic cluster distortions appear to be characteristic features of the white light emitting material. In the other material, cores are undistorted and core distances are larger. There, the formation of nanocrystalline structures in the amorphous matrix could also be identified as reason for the WLG suppression.