New Exciton Bands in KJ:Na Crystals Containing A‐Centres

Abstract

Type A‐centres are found in KJ:Na single crystals. The conversion F → A is followed in the visible region and near the fundamental absorption edge. The intensity of the β‐band decreases with the formation of A‐centres and at the same time a new band (βA) is formed at longer wavelengths. The disappearance of A‐centres results in a broad Ac‐band in the visible region which is accompanied by the formation of an αA‐band in the ultra violet region, at wavelengths shorter than those corresponding to the α‐band. As the intensities of the A1‐and βA‐bands are proportional the occurrence of the βA‐ and αA‐bands can be explained qualitatively by exciton formation near A‐centres or vacancies which are due to negative ions with a Na ion as nearest neighbour.

Exciton Absorption in the Presence of ExcitedFCenters

“…12 More recently new exciton bands were found in crystals containing FA centers, i.e., F centers formed next to a cation impurity; PA and a A were observed in KG, 13 KBr, 13 and KI 14 with Na + impurities. In addition a 7 band, 15 higher energy exciton bands of a centers 13 and absorption bands associated with H~ and Brinterstitials in KC1 13 were found.…”