The nature of blue luminescence from natural benitoite BaTiSi₃O₉

It is proved that blue luminescence from benitoite is connected with intrinsic luminescence centers, namely isolated TiO₆ octahedra. The metastable level ³T_1u is the emitting level at low temperatures with a long decay time of 1.1 ms. At higher temperatures an energy level with higher radiation probability must be involved in the emission process, and this level is situated at 0.06 eV higher than the lowest level. These two levels may be connected with ³T_1u level splitting or with closely spaced ³T_1u and ³T_2u levels. Decay time shortening and thermal quenching are connected with nonradiative decay within the TiO₆ luminescence center, while energy migration does not take place at least up to room temperature.