Mechanism of the Luminescence Enhancement of SrSi₂N₂O₂:Eu²⁺Phosphor via Manganese Addition

The addition of Mn-O-based compounds during the solid-state synthesis of SrSi₂N₂O₂:Eu²⁺significantly increases the luminescence intensity of this phosphor. Hitherto, this effect was explained as the energy transfer between Eu²⁺and Mn²⁺ions. Using electron paramagnetic resonance and optical techniques, we show that Mn is not incorporated into the SrSi₂N₂O₂host; nevertheless, attempts to dope improve the luminescence quantum yield (QY) of this compound. Moreover, we found that codoping exertion with Mn ions in the synthesis process may also cause the enhancement of persistent luminescence and mechanoluminescence. It is also shown that the structure of the primary defects in SrSi₂N₂O₂:Eu²⁺does not change by adding Mn during the synthesis of this oxynitridosilicate, except their concentration. The changes of the radiative decay time of Eu²⁺induced by attempts of codoping are responsible for the observed increase of the luminescence QY of this phosphor.