Suppressed Self-Reduction of Manganese in Mg₂SnO₄ via Li⁺ Incorporation with Polychromatic Luminescence for Versatile Applications

Herein, the self-reduction behavior of manganese (Mn) in Mg₂SnO₄ (MSO) host lattices prepared by using the solid-state reaction technique in air atmosphere is reported. Excited by 282 nm, only the emission of Mn²⁺ is seen, and the observed results are confirmed by theoretical calculation based on the density functional theory. Noteworthy, with the codoping of Li⁺, the self-reduction process of Mn is suppressed, leading to the coexistence of Mn²⁺ and Mn⁴⁺ in MSO host lattices along with the multicolor emissions. For the suppressed self-reduction behavior, possible hypotheses are proposed to elucidate the corresponding mechanisms. Furthermore, benefiting from the different thermal quenching behaviors of Mn²⁺ and Mn⁴⁺, ratiometric optical thermometers with high sensitivity of 6.59% K⁻¹ are designed. Moreover, the prepared phosphors possess a good green afterglow phenomenon, in which their trap depth are 0.71 and 0.91 eV. In addition, via using the designed phosphors, applications in anti-counterfeiting, fingerprint identification, and optical information storage are also realized.