Photoluminescence Properties of Double Perovskite Tantalates Activated with Mn⁴⁺, AE₂LaTaO₆:Mn⁴⁺ (AE = Ca, Sr, and Ba)

Tetravalent manganese is known as one of the candidate luminous centers to obtain red emission. There are still unclear factors in Mn⁴⁺-activated oxide phosphors to achieve intense emission. In this paper, we studied the photoluminescence properties of double perovskite-type tantalates AE₂LaTaO₆ (AE = Ca, Sr, and Ba) activated with Mn⁴⁺. All AE₂LaTaO₆:Mn exhibited Mn⁴⁺-emission in the deep red region under excitation by near-ultraviolet-green light (300-570 nm) at room temperature. Co-substitution of Mg²⁺, Al³⁺, and Ti⁴⁺ compensates unbalanced charge caused by oxygen defects, resulting in the enhancement of Mn⁴⁺-emission. The present cosubstitution effect is different from the usual cosubstitution, such as the replacement of two Al³⁺ by Mn⁴⁺ and Mg²⁺, taking into consideration the charge balance between cations. Theoretical calculation of band structures based on density functional theory suggests the presence of two kinds of quenching schemes in AE₂LaTaO₆:Mn, photoionization and electron transfer from valence band to t_2g orbitals of Mn.