Cathodoluminescence of Terbium- and Ytterbium-Activated Oxyfluoride Glasses and Glass Ceramics

Cathodoluminescence (CL) spectra and decay times have been studied for oxyfluoride glasses and glass ceramics of the system: SiO2 - Al203 - Na2O - LaF3 - NaF, activated by terbium and ytterbium. The CL spectra of the glasses and glass ceramics show characteristic Tb3+ luminescence bands: blue (5D3 → 7FJ) and green (5D4 → 7FJ) groups. With increasing terbium concentration the blue- to green-group ratio decreases. The CL decay curves can be sufficiently well approximated by two exponents - fast and slow. Decay times for the blue-group CL bands are faster than for those of green group. As the terbium concentration increases, the lifetimes for the lines of the blue group shorten, while for the green group they remain unchanged. This could be explained by the cross-relaxation between the transitions 5D3 → 5D4 and 7F6 → 7F0 of two terbium ions.