Mn²⁺ activated green, yellow, and red long persistent phosphors

Mn²⁺ activated long persistent phosphors, CaAl₂O₄:Mn²⁺, Ce³⁺, Ca₂Al₂SiO₇:Mn²⁺, Ce³⁺ and MgSiO₃:Mn²⁺, Eu²⁺, Dy³⁺, were prepared. Long persistent phosphorescence in green, yellow, and red have been observed in the systems with persistence time over 10 h for the green (525 nm) and the yellow (550 nm) and 4h for the red (660 nm). Emission and excitation spectra showed that Mn²⁺ emission was dominant in these materials. Long persistent phosphorescence was also measured in the systems without Mn²⁺ as a co-dopant. The emissions were much stronger due to 5d-4f transitions in Ce³⁺ and Eu²⁺ other than 3d-3d transitions in Mn²⁺. The disappearances of the long persistent afterglow in these systems when co-doped with Mn²⁺ suggested the existence of a strong persistent energy transfer from Ce³⁺ and Eu²⁺ to Mn²⁺.