Optical properties of Li2B4O7 glasses doped with rare-earths and transition metal ions

Absorption and emission spectra of Cr, Eu and Dy ions in Li2B4O7 glasses melted in oxygen and hydrogen were measured for valency states and excited states analysis. It was stated that the presence of Cr6+ ion is limited by composition of the starting mixture and atmosphere of the melting and that this ion arises as Cr6+O4 complex. The 308 run line excites the Li2B4O7:Cr glass within the highest absorption peak which can be ascribed to the following charge transfer transition: Cr6+O4(3d(0)2p(6))--> Cr5+O-(3d(1)2p(5)). Under gamma irradiation Cr6+O4 complex of 3d(0) configuration can be disintegrated giving additional absorption bands of Cr3+ and may be Cr4+ centers at tetrahedral sites. One of these additional absorption bands is responsible for 430 run emission.