“Eu2+-doped Na3Sc2(PO4)3 ionic conductor, a promising phosphor for high-power lighting, has superior thermal quenching resistance. This study explores the mechanism of negative thermal quenching (NTQ) through upconversion (UC) and downshifting (DS) luminescence of Yb3+/Er3+, revealing that thermally accelerated dynamic defects/ions contribute to NTQ of UC luminescence and thermally stabilized DS luminescence by promoting radiative transition and suppressing non-radiative transition.”