Novel persistent and tribo-luminescence from bismuth ion pairs doped strontium gallate

Unlike the many transition metal ions- and rare earth ions-doped long persistent materials, at present, few bismuth ion-doped long persistent materials have been reported. In this work, we report on a novel phosphor Sr₃Ga₄O₉:Bi³⁺ that combines photoluminescence, long persistent luminescence and triboluminescence at room temperature. The compound glows in the green (530 nm) and red (680 nm) spectral regions upon excitation in the range 240-400 nm. From calculation results based on the original theory of electronegativity, we obtain the energy level structure of Bi³⁺ (doped into Sr sites 1-3) in Sr₃Ga₄O₉:Bi³⁺, from which it is inferred that these emissive features are ascribed to Bi³⁺ pairs. These emissions are also produced under mechanical action and show a persistence up to 6.5 hours after removal of ultraviolet super-bandgap irradiation. This is the first observation of such multi-functionality for an inorganic solid activated with Bi³⁺. Furthermore, considering our insights into the elusive nature of Bi³⁺ luminescence, we expect that the Bi³⁺-doped mechanoluminescence (ML) material will further promote the development of ML.