Dresden 2009 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 14: Photonic Dielectrics III
DF 14.7: Vortrag
Donnerstag, 26. März 2009, 12:20–12:40, WIL A317
Temperature dependent Urbach tail measurements of CaF2 single crystals — •Martin Letz1, Alexander Gottwald2, Mathias Richter2, and Lutz Parthier3 — 1Schott AG, Research and Development, D-55014 Mainz — 2Physikalisch-Technische Bundesanstalt, D-10587 Berlin — 3Schott Lithotec AG, Otto-Schott Str. 13, D-07745 Jena
In the deep ultra-violet spectral range the transmission of high purity CaF2 was measured using synchrotron radiation. In the vicinity of the band gap below 11.2 eV or for wavelength longer than 90 nm, a scaling behaviour of the absorption as a function of photon energy was observed. Temperature dependent measurements allow to distinguish different absorption mechanism which differ by their ability to couple to phonon excitations. These two types of Urbach tails were analyzed. The origin of the temperature independent tail is due to defects in the lattice whereas the temperature dependent part originates from short time localization of exciton modes coupling to lattice distortion.