Luminescence-spectral properties and structure of optical centers in Eu- and Ce-Eu-containing quartz gel-glasses

Eu- and Ce-Eu-containing quartz glasses obtained by a direct sol-gel-glass transition are investigated. It is discovered that the conversion of a xero gel into a glass leads to lowering of the symmetry of the Eu3+ optical cent ers from hexagonal to orthorhombic and a many-fold increase in the efficien cy of the excitation of their luminescence through the charge-transfer band . In the co-activated glasses, the distortion of these centers is enhanced, and compound Ce4+-Eu3+ centers appear, in which the Eu(III) oxo complexes are characterized by cubic symmetry and by sensitization of the luminescenc e of the Eu3+ ions by photoreduced (Ce4+)(-) ions. Crystal-field theory sho ws that the coordination number of the cation in such oxo complexes is equa l to 8. It is established that similar structural formations exist in annea led xerogels, but they are manifested spectroscopically only upon low-tempe rature shortening of the interatomic distances, as a result of which the se nsitization indicated becomes possible. (C) 1999 American Institute of Phys ics. [S1063-7834(99)00902-8].