ORIGIN OF THE F-AGGREGATE CENTERS IN BAFX (X = CL, BR) SINGLE-CRYSTALS

Some new experimental evidence to determine the origin of the F-aggreg ate centers located in the near IR region in BaFX(X=Cl. Br) crystals i s demonstrated. The attribution of the F-aggregate bands to a cluster of the F(X-) centers has been confirmed through a series of measuremen ts on their emission in IR and the process of aggregates formation in BaFCl1-xBrx mixed system. The F-aggregate bands at 860 and 1100 nm are assigned to the F(X-)(2) and F(X-)(4) centers, respectively, in view of the equilibrium between the F(X-) centers and the F-aggregate cente rs.