Optical properties of Li_2B_4O_7 glasses doped with rare-earths and transition metal ions

摘要

Absorption and emission spectra of Cr, Eu and Dy ions in Li_2B_4O_7 glasses melted in oxygen and hydrogen were measured for valency states and excited states analysis. It was stated that the presence of Cr~(6+) ion is limited by composition of the starting mixture and atmosphere of the melting and that this ion arises as Cr~(6+)O_4 complex. The 308 nm line excites the Li_2B_4O_7:Cr glass within the highest absorption peak which can be ascribed to the following charge transfer transition: Cr~(6+)O_4(3d~02p~6) → Cr~(5+)O~-(3d~12p~5). Under gamma irradiation Cr~(6+)O_4 complex of 3d~0 configuration can be disintegrated giving additional absorption bands of Cr~(3+) and may be Cr~(4+) centers at tetrahedral sites. One of these additional absorption bands is responsible for 430 nm emission.