On the coloration properties of CaF2 : Na

Abstract

We have investigated the dichroic properties and the existence of metastable excited states of several colour centres created by X-irradiation in CaF 2 :Na. According to our results absorption bands peaking at 600, 385 and 322 nm are associated to the same centre which behaves optically as orthorhombic. The lack of observation of a metastable state is in favour of the F 2A + model for this centre. On the other hand the band at 500 nm and another absorption at 322 nm are proved to belong to the same centre which behaves optically as tetragonal. A metastable excited state of this centre with lifetime of 0,83 s at 77 K has been detected. Two possible models are discussed for this centre Etude des proprietes dichroiques et de l'existence d'etats excites metastables de plusieurs centres colores crees par irradiation X