NH ₄ ⁺ ‐Induced Formation of Hexagonal‐K _1.5 (NH ₄ ⁺ ) _0.5 SiF ₆ :Mn ⁴⁺ with Polarized Zero‐Phonon Line Emission

Abstract Polarized luminescence is extensively applied in many cutting‐edge areas, implying the practical significance of exploring the polarization behavior of various emitters. Herein, for the first time, the polarized emission of Mn 4+ ion is disclosed in a hexagonal K 2 SiF 6 matrix, which is obtained through the NH 4 + ‐induced phase transition from the cubic counterpart. The exact component of the hexagonal matrix is determined to be K 1.5 (NH 4 ) 0.5 SiF 6 . After doping Mn 4+ , the K 1.5 (NH 4 ) 0.5 SiF 6 :Mn 4+ exhibits intensive zero‐phonon line (ZPL) emission. Importantly, the ZPL emission shows a linear polarization with a degree of polarization (DOP) of 0.65, and its polarization direction is aligned with the c ‐axis of the crystal. The polarization behavior arises from the Mn 4+ ions occupying lattice sites with anisotropic structure along the c ‐axis. The rest of Mn 4+ ‐emissions, which incorporate phonons, show the same polarization direction but with much weaker polarization (DOP ≈ 0.1). Moreover, when excited by the 488 nm light propagating perpendicularly to the crystal c ‐axis, all the emissions show a periodic fluctuation with the polarized angle of excitation. This work conducts a pioneering and detailed study of the polarization behavior of Mn 4+ ‐emission in a newly established hexagonal fluoride, opening up the research of polarized luminescence in the abundant Mn 4+ ‐doped phosphors.