Terbium(III)-doped mesoporous silicas were synthesized, and the states of terbium ions in the silica frameworks were investigated. The mesopores were preserved upon doping at terbium ion molar concentrations relative to (Si+Tb) up to 15 mol %, indicating the interaction of terbium ions with Si–O bonds. Significant morphological changes of the particles were observed with increasing the doping concentration. The shapes of the photoluminescence spectra due to the transitions of ⁵D<inf>4</inf>→ ⁷F<inf>6</inf>and ⁵D<inf>4</inf>→ ⁷F<inf>5</inf>were indicative of the presence of terbium ions in the silica matrix, and the quantum efficiency (2.1–2.8%) and lifetime (1.6–1.9 ms) decreased with increasing the doping concentration up to 15 mol %. Therefore, the terbium ions are considered to be located inside the amorphous silica frameworks, where they electrostatically interact with the O atoms of silanol and siloxane groups.