Fig. 4: Time evolution of Eu2+ populations at excited states.

a Estimated from GA-driven and b PSO-driven Runge–Kutta processes. The curves represent regular donors (\({D}^{{{\rm{e}}}}\)), defective donors (\({\bar{D}}^{{{\rm{e}}}}\)), regular acceptors (\({A}^{{{\rm{e}}}}\)), defective acceptors (\({\bar{A}}^{{{\rm{e}}}}\)).