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Compton, W.D. LeCorgne, Denis York 2011-07-27T15:16:36Z 2011-07-27T15:16:36Z 10000-01-01 1970 The influence of uniaxial stress upon three types of imperfections occurring in the alkali halide crystal lattice has been investigated. The imperfections are the interstitial atom, the interstitial ion, and the negative ion vacancy. The interstitial atom, or H center, is a paraelastic defect which assumes a preferential crystal orientation in the field of an external mechanical stress. From the results of the reorientation kinetics - studies, it was possible to show that H centers are not stable in the KBr crystal lattice above 2SoK. At temperatures higher than 2SoK, the H centers are transformed into two new paraelastic defects, H(ii) and H(iii), possessing the same optical absorption band as the H center but differing both from the H' center and from each other in their reorientation kinetics. A study of the wavelength dependence of the H, H(ii), and VI (Na+) centers s~owed the 'existence of three similar-polarized transitions for each of these defects. One of these transitions, located at 230 run for all of the defects studied, was determined to be too high in energy to be explained by the simple X2 - level scheme. In addition, a comparison of various properties of the four defects indicates that the last three can be described as perturbed H centers. Dichroism measurements, performed as a function of temperature and wavelengt, h on the 230-nm I band in KBr, showed this band to be a composite of a band at 234 nm due to the I center and a band at 230 nm attributed to the H center. The I center dichroism was isolated and was observed under various experimental conditions. The results of these observations are consistent with a body-centered model for the I center in which the I-center absorption band is attributed to the excitation of a p-like electron on the interstitial Br- ion. Similar measurements were also perfonned on the a band in KI. The a-band dichroism measurements were found to be consistent with an electronic transition from an s-like ground state to a p-like excited state, indicating that the a center is best described as a quasi-molecule. Submitted by Carolyn Mead (cmead2@illinois.edu) on 2011-07-27T15:16:36Z No. of bitstreams: 1 1970_lecorgne.pdf: 4035900 bytes, checksum: b3df9f8d1f8285ce61b4fa54bbf76bc5 (MD5) Made available in DSpace on 2011-07-27T15:16:36Z (GMT). No. of bitstreams: 1 1970_lecorgne.pdf: 4035900 bytes, checksum: b3df9f8d1f8285ce61b4fa54bbf76bc5 (MD5) Previous issue date: 1970 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Carolyn Mead (cmead2@illinois.edu) on 2011-07-27T15:16:36Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:33:20-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Thesis Thesis U of I Only 6050536 http://hdl.handle.net/2142/25855 en 1970 Denis York LeCorgne applied uniaxial stresses ultraviolet absorption bands Potassium bromide (KBr) Potassium iodide (KI) interstitial atom Influence of applied uniaxial stress upon the ultraviolet absorption bands in KBr and KI Dissertation / Thesis text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.