Effect of A-site deficiency on perovskite-type Mn4+-activated La5/3MgTaO6 red phosphor and green luminescence of the Mn2+ occupied six-coordinate site in Mg2LaTaO6

White light LEDs have a long life and high energy efficiency; however, their application is limited owing to the lack of red components. Herein, we use the solid-state reaction method to fabricate a new Mn-activated perovskite-type La5/3MgTaO6 phosphor that exhibits red emission under UV excitation at 365 ​nm. A-site deficiency in the perovskite-type structure plays a crucial role in the emission of Mn4+ in La5/3MgTaO6 because Mn4+—which is located in the non-inversion symmetry site—is activated for such an emission. In addition, the newly Mn-activated pyrochlore-type Mg2LaTaO6 phosphor exhibited green emission under UV excitation at 254 ​nm owing to the oxide ion deficiency of Mg2LaTaO6. Based on the features of the oxide-deficient pyrochlore-type structure, we infer that Mn2+ may be present in the six-coordinate octahedral site with high distortion in pyrochlore-type Mg2LaTaO6.