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Title: A study of ytterbium and europium in the alkali halides
Author: Bland, Stephen Wilfrid
ISNI:       0000 0001 3467 6752
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1985
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Ytterbium and europium have been successfully diffused from the vapour phase into the alkali halides. Both impurities are incorporated in the divalent state and give rice to optical absorption bands in the ultraviolet due to transitions of the type 4fn - 4fn-15d. Optical absorption spectra for the Yb2+ ion in the alkali halides are, with the exception of NaCl, reported for the first time. Generally excellent agreement is obtained between experiment and a theory utilising the Jij-coupling scheme to describe Yb2+ in an octahedral crystal field, provided that a correction based on the nephelauxetic effect is taken into account. Certain additional absorption bands are associated with transitions of the type 4f14 - 4f13g(A1g), where g(A1g) represents a a-bonding orbital created between the 6a orbital of the Yb2+ ion and a a orbital of the surrounding octahedrally coordinated anion complex. Optical absorption spectra are also recorded for the Eu2+ ion, of which the spectrum for KFi2Eu2+ has not been reported previously. Electron spin resonance (ESR) spectra obtained for the Eu2+ ion confirm the presence of a cation vacancy along the <110> direction. The ESR spectrum for Eu2+ on a conventional orthorhombic site in KF is reported for the first time. The diffusion of either ytterbium or europium into NaF results in the formation of a separate phase of YbF2 or EuF2 respectively. Phases of the type EuX2 are also observed in thermally aged NaCl and NaBr crystals. A new coloration technique known as aliovalent coloration is described for the alkali halides. Coloration consists of a number of concentric zones and these are investigated by use of a novel traversing-slit apparatus. New colour centres based on water related defects are observed in KF. A new defect centre la also observed in KCl and KBr. This is attributed to a U-centre perturbed by an impurity-vacancy complex.
Supervisor: Not available Sponsor: Science and Engineering Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics