Danburite (a naturally occurring borosilicate mineral and crystalline analogue of borosilicate glass) was studied by using 2-dimensional correlation electron spin echo envelope modulation spectroscopy. The structure of the prevalent radiation-induced defect in this mineral, a B-O hole center, was determined. The hole was trapped, by non-bridging O, in a strongly distorted -O3B-O--BO3- linkage. The precursor of the hole center was a Ca2+ vacancy. These results and computer modelling suggested that, in borosilicate glasses, the hole center was the same >B-O- radical as that in alkali borate glasses. It was suggested that a >B-O- unit near to a cation vacancy was the precursor of hole centers in both types of glass.

On the Structure of Trapped Holes in Borosilicates. I.A.Shkrob, V.F.Tarasov: Journal of Chemical Physics, 2000, 113[23], 10723-32