Super long ultraviolet-A persistent luminescence and photo-stimulated luminescence from CaMgGeO4: Bi3+

Abstract

Here, we have developed a novel ultra long ultraviolet-A afterglow material CaMgGeO₄: Bi³⁺, which shows more than 24 h UVA afterglow emission peaked at 346 nm. The crystal structure shows that the prepared sample is a pure phase with an orthogonal system of Pmnb space group. The composition of valence band and conduction band was analyzed by the density of states, which reveals that the bandgap of the CaMgGeO₄ matrix is 3.69 eV. The photoluminescence spectrum of the sample consists of a broadband in the 320–400 nm UVA region, which belongs to the ³P₁ → ¹S₀ electron transition of Bi³⁺. More importantly, under the excitation of ultraviolet lamp for 3 min, CaMgGeO₄: Bi³⁺ exhibited an UVA ultra long persistent luminescence (LPL) with a duration of more than 24 h, which afterglow emission intensity still reaches 1500 cps and is about 6 times of the background intensity. In addition, the UVA emission of CaMgGeO₄: Bi³⁺ after 13 h day can be repeatedly by short periods of low-energy light sources stimulation. The thermoluminescence analysis indicates that the presence of shallow and deep traps is responsible for excellent UVA-LPL and photo-stimulate luminescence (PSL). The excellent LPL and PSL properties can prompt CaMgGeO4: Bi³⁺ phosphor to be widely used in the field of photodynamic therapy.