We use cookies to ensure that we give you the best experience on our website. By continuing to browse this repository, you give consent for essential cookies to be used. You can read more about our Privacy and Cookie Policy.

Durham e-Theses
You are in:

Some optical properties of the alkali halides containing divalent impurities

Ridley, B. K. (1957) Some optical properties of the alkali halides containing divalent impurities. Doctoral thesis, Durham University.



The investigation was limited mainly to NaCl.Mn++ and NaCl.Ca++, and was concerned with colour centres in single crystals of these materials. The crystals were grown by the Kyropoulis technique and optical absorption measurements were made with a grating spectrophotometer. The emphasis of the work was placed on the production of Z-bands in NaCl. Ca++ but the effects of optical and thermal bleaching and of quenching were investigated in all crystals. The results of the work on NaCl.Mn++ confirmed the model of Schneider and Caffyn (1955) in which the Mn++ ions and positive ion vacancies are deposited at dislocations and become more uniformly distributed after quenching. In particular, it was found that quenched crystals were luminescent after being X-rayed, indicating the presence of dispersed Mn++ ions; a similar result was found in NaCl .Ni++. A short study of the distribution of Mn++ in crystals was also made. It was found that Mn++ and Ni++ gave rise tocharacteristic bands in the ultra violet, a weakband at 275 Mµ with Mn++, a strong band at 247 mµ with Ni++. The presence of a band at 255 mµ in NaCl.Cu++ was confirmed. No evidence was obtained for the formation of Z-bands by Mn++, Ni++ or Cu++. Calcium was found to be much more soluble in NaCl than manganese, and enhanced the colourability proportionately less, pointing to a close relationship between solubility, mis-match, and the production of negative ion vacancies. Analysis of the F-band in coloured NaC1.Ca++ crystals indicated that Z- centres were formed by X-rays. Quenching enhanced the number of Z-centres, indicating a deposition at dislocations similar to that found for manganese. Evidence for the formation of both Z(_1)- and Z(_2)- centres by X-irradiation was found. In crystals containing a high proportion of Ca++ a band at 345 mp, which is probably to be associated with Ca++- positive ion vacancy complexes, was prominent. The results of an investigation of the effect of concentration of Ca++ on the growth of the F- and Z-bands indicated that a Ca++ ion introduced about ten negative ion vacancies into the crystal. On the basis of a statistical mechanical model of the formation of Z-centres it was inferred that of the Ca++ ions producing Z-centres no more than 2% were associated with positive ion vacancies, confirming the work of Etzel (l952). It was also inferred that the activation energy associated with the liberation of Ca++ ions from dislocations to form incipient Z-centres was 1.9 eV, a value which agreed well with an estimated value. Factors influencing the width of the F-band are also discussed.

Item Type:Thesis (Doctoral)
Award:Doctor of Philosophy
Thesis Date:1957
Copyright:Copyright of this thesis is held by the author
Deposited On:14 Mar 2014 17:06

Social bookmarking: del.icio.usConnoteaBibSonomyCiteULikeFacebookTwitter