Low-temperature absorption spectroscopy (cryoabsorption spectroscopy)

Abstract

Reducing the temperature of many substances produces characteristic changes in their absorption spectra: increase in absorbance bands, reduction of their half-band width, changes in the number of bands or lines, and shifts in the position of absorption maxima.

Observation of Core Phonon in Electron–Phonon Coupling in Au25 Nanoclusters

“…The atomic-level structures of metal NCs provide ideal systems to probe the correlation between the structure and optical/electronic properties of these ultrasmall nanomaterials. − While much work has been carried out toward achieving the correlations, many fundamental issues still remain, for instance, the correlation between the structure and carrier dynamics of Au NCs; , in particular, how does the electron–phonon coupling affect the photoexcited carrier lifetime? − Temperature-dependent optical absorption measurements can provide insights into the fundamental electron–phonon coupling since cryogenic measurements offer a direct way to extract information on electron–phonon coupling and phonon modes . In previous work, this method has been commonly used to characterize conventional semiconductors, perovskite materials, and conjugated organic molecules. − However, temperature-dependent optical properties of Au NCs are still barely studied.…”

“…Among all the temperature-dependent optical absorption features, the shift of absorption maximum is the most valuable one, because it indicates a change to the corresponding electronic transition gap and such a change discloses information on thermal lattice contraction/expansion and electron–phonon coupling. − Ramakrishna et al , previously applied a modified Bose–Einstein relationship that was developed by O’Donnell and Chen to model the absorption peak dependence on the temperature and obtained the electron–phonon coupling strength and average phonon energy for Au NCs in solution. Here, we use the same method to analyze the temperature-dependent energy gap ( E g ) in our solid film samples.…”