Excess Electron Colour Centres in NaF

Abstract

Fine powder of NaF was coloured in an electrodeless discharge. Colour centres were studied by measuring the diffused reflectance. It was possible to obtain a large concentration of F aggregate centres. Besides the well known bands at 342 nm and 505 nm corresponding to the F and M centres respectively, two additional absorptions peaking at 440 nm and 630 nm were observed. From bleaching studies they are attributed to excess electron centres. It is shown that their formation is strongly temperature dependent. The band at 440 nm corresponds to the R₂ band. To our knowledge no N band has been reported so far in NaF powder. The band at 630 nm is attributed to N centres. An Ivey type relation for the N band peak positions in alkali halides is suggested.