Influence of temperature and pressure on shape and shift of impurity optical bands in polymer glasses

The Journal of Physical Chemistry. a
Indrek Renge

Abstract

The shape, broadening, and shift of optical absorption spectra of molecular impurity centers in polymer glasses are considered in terms of inhomogeneous energy distributions and coupling of electronic transitions to vibrations. Persistent spectral hole burning was applied for frequency-selective probing of zero-phonon lines. The shift and broadening of spectral holes were studied between 5 and 50 K and by applying a hydrostatic He gas pressure up to 200 bar. Broadband absorption spectra were recorded between 5 and 300 K in poly(methyl methacrylate) and polyethylene. In addition to "normal" thermal broadening, due to the first- and second-order electron phonon coupling, several narrowing components were predicted on the basis of frequency dependent hole behavior. Thermal expansion of the matrix and the relaxation of local strains, previously accumulated on cooling below the glass temperature can lead to shrinking of the inhomogeneous width. A Voigt treatment of absorption band shapes reveals that the Gaussian component can indeed suffer remarkable narrowing. Inhomogeneous band shapes and the frequency-dependent thermal and baric line shifts were rationalized with the aid of a pair of two-body Lennard-Jones potentials. The shift ...Continue Reading

Citations

Aug 29, 2013·Chemical Reviews·G Andrés CisnerosCeleste Sagui
Oct 30, 2012·Nucleic Acids Research·Mahmoud MoradiCeleste Sagui
Apr 10, 2012·Annual Review of Chemical and Biomolecular Engineering·Sadanand SinghJuan J de Pablo
Jul 28, 2007·The Journal of Chemical Physics·Indrek Renge
Apr 2, 2008·The Journal of Chemical Physics·W L LiuW H Su
Dec 12, 2012·Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy·Indrek Renge, Koit Mauring

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