| description: |
The essence of proposal are studies of local dynamics, including metastability-related phenomena, in incommensurate phases of molecular solids (biphenyl, bis (4-chlorophenyl) sulfone) by means of high-resolution optical spectroscopy (spectral hole burning, 2D excitation-emission spectroscopy, ODMR etc.) of probe molecules. Incommensurate solids form a fundamentally interesting subclass of solids between crystals and less disordered solids. The main goal of the project is measurement of such spectral characteristics of the probe molecules as the inhomogeneous distribution function, holewidths etc. at different temperatures and pressures in both incommensurate and commensurate (reference) phases in order to establish spectral "fingerprints" of incommensurability. We hope to make distinction between the effects characteristic for theromodynamic equilibrium and the ones due to metastability and transitions between different phases. Beside the "pure" systems (containing only the probe dopant at low concentrations) we plan to study mixed systems with higher concentration of guest molecules. There exists evidence that some dopants may efficiently inhibit formation of incommensurability, to establish the spectral characteristics of such transformation is one of our goals. We also plan to study further the found by us universal (independent on the probe) mechanism of spectral hole burning and situtations, where the assumed global metastability is locally strongly disturbed by dopant phototransformations. Hopefully the latter results may shed additional light on some phenomena we earlier have observed in molecular glasses. Search for novel probe molecules is planned in order to distinguish the effects due to specific probes from the characteristics of host solid. The experimental results hopefully allow for proof and development of existing theoretical models. |