Deep-red-emitting phosphors of Mn⁴⁺-activated tantalite for high-sensitivity lifetime thermometry and security films

Herein, single monoclinic phase Mn⁴⁺-doped Sr₂InTaO₆ (SITO) phosphors were reported in terms of both luminescence behaviors and potential applications. The optimal Mn⁴⁺-doped SITO (0.3 mol%) exhibited a good color purity of 92.9% in a deep-red region with a chromaticity coordinate of (0.707, 0.293). In addition, the local structure of Mn⁴⁺ in the SITO matrix was determined. The crystal-field strength was calculated to be approximately 1781.7 cm^-1 whereas the nephelauxetic ratio was determined to be 1.04. Furthermore, the flexible SITO:Mn⁴⁺-YAG:Ce³⁺ security film was fabricated for use in anti-counterfeiting applications, which could emit different colors under various lighting sources. The SITO:Mn⁴⁺ phosphors exhibited a high sensing sensitivity based on the luminescence lifetime. Consequently, the SITO:Mn⁴⁺ phosphors can be employed in bifunctional platforms of luminescence lifetime thermometry and anti-counterfeiting applications.