Colour Centres in X‐Irradiated NaCl:Ag and NaCl:(Ag + Ca) Crystals

Abstract

A study is made of colour centres induced by X-irradiation a t room temperature in NaC1:Ag and NaCl: (Ag + Ca). It is shown that the induced bands in NaCl: Ag are strongly dependent on the concentration of Ag as well as on the irradiation time and also that the B-, C-, and D-bands have a complex structure. Three components of the B-band, four of the C-band and two of the D-band are found at liquid nitrogen temperature. Optical bleaching in the F-light shows that only a component of the B-, C-, and D-bands is definitely electronic. It is also noted that only the optical bleaching of the F-band in NaC1:Ag results in a simple B-band much like that obtained by electrolytic colouring. The incorporation of both Ca and Ag in NaCl and subsequent X-irradiation lead t o very intensive B-and Dbands which are shifted t o shorter wavelengths compared with those bands in crystals containing only Ag. The optical bleaching experiments on these crystals suggest that colour centres containing both Ca and Ag are probably formed, as in the case of similar crystals electrolytically coloured.In NaCl: Ag und NaCl: (Ag + Ca) werden Untersuchungen an Farbzentren durchgefuhrt, die durch Rontgenbestrahlung bei Zimmertemperatur erzeugt werden. Die induzierten Banden in NaCl werden stark von der Ag-Konzentration und der Bestrahlungsdauer beein-fluBt, und die B-, Cund D-Banden zeigen eine komplizierte Struktur. Drei Komponenten der B-Bande, vier der C-Bande und zwei der D-Bande werden bei der Temperatur des fliissigen Stickstoffs gefunden. Optisches Bleichen im F-Licht zeigt, da13 nur eine Komponente der B-, Cund D-Banden eindeutig elektronisch ist. Auch fiihrt nur optisches Bleichen der F-Bande in NaCl: Ag zu einer einfachen B-Bande genau nie bei elektrolytischer Verfiirbung. Der Einbeu von Ce und Ag in NaCl mit darauffolgender Rontgenbestrahlung ergibt intensive B-und D-Banden, die im Vergleich zu Kristallen, die nur Ag enthalten, nach kiirzeren Wellenliingen verschoben sind. Die Experimente an diesen Kristallen weisen darauf hin, daB hauptsachlich Farbzentren gebildet werden, die sowohl Ca als auch Ag enthalten, wie im Falle ahnlicher Kristalle, die elektrolytisch verfarbt werden.

Absorption and Emission Spectra of NaCl:Ag Crystals Containing Oxygen and Calcium Impurities

“…But though the calcium concentration is very low, some absorption a t 250 nm ( K x 1 cm-l) and 260 nm is still there. From our data we cannot conclude, as previously suggested [4], that the absorption bands a t 250 and 260 nm depend on the calcium content and do not appear in crystals containing no calcium.…”

“…I n the ultraviolet between 200 and 230 nm a series of absorption bands show up which have been attributed to vibronically allowed transitions 4d10 --f 4dQ5s in the Ag+ ion [3]. Adjacent to these well-known Ag+ absorption bands we found in most of our Ag+-doped NaCl crystals absorption bands at 250, 260, and occasionally also at 231, 240 nm.l) Tope and Haragea [4] have seen these four bands when they measured NaCl crystals doped with silver and calcium at -180 "C. These authors speculated that the centre causing the four absorption bands might possibly be due to an Ag, Ca, and 0 combination.…”

Properties of the B‐centre in additively coloured Ag+ doped KCl crystals

“…Etzel and Schulman suggested that the B-band would be due to an electron trapped on a silver ion in the vicinity of a vacancy [2]. Furthermore, it was shown by Topa and Haragea [3] that the B-bands in X-rayed and electrolytically coloured NaC1:Ag crystals are not the same. This paper presents properties of the Bcentres in additively coloured silver-doped KC1 crystals.…”