SINGLE MOLECULE SPECTROSCOPY IN A SOLID

By exciting a very small volume of an inhomogeneously broadened solid solution at a very low concentration of guest molecules, it is possible to spectrally resolve its inhomogeneous fluorescence excitation spectrum into the set of sharp homogeneous peaks of the composing single molecules. Intensity, shape, width and distribution of the peaks are all consistent with their attribution to single molecules, but a definite proof of this is given by the correlation properties of the fluorescence light: due to intersystem crossing, the fluorescence of a single molecule exhibits photon bunching. The study of single molecule peaks as temperature is varied displays the variety of possible molecular microenvironments.