⁵D ₃→ ⁷F _J emission of Tb doped solgel silica

Amorphous silica samples doped with 0.1 and 1 mol% of terbium (Tb) were synthesized by the solgel method. In addition to the green light associated with ⁵D ₄→ ⁷F _J transitions of Tb ³⁺, the sample containing 0.1 mol% also emitted blue light as a result of ⁵D ₃→ ⁷F _J transitions during photoluminescence (PL) measurements. As a result of concentration quenching this blue emission was not observed for the samples doped with the higher concentration (1 mol%). However the blue ⁵D ₃ → ⁷F _J emission was observed in the 1 mol% doped samples during cathodoluminescence (CL) measurements. Since a rough calculation indicated that the excitation rate in the CL system where the blue emission is observed may be similar to a laser PL system under conditions where the blue emission is not observed, the difference is attributed to the nature of the excitation sources. It is suggested that during the CL excitation incident electrons can reduce non-luminescent Tb ⁴ ions in the silica, substituting for Si ⁴ ions, to the excited (Tb ³⁺) state and that these are responsible for the blue emission, which does not occur during PL excitation.