Mn–Mn Magnetic Coupling Interaction-Induced Red Emission in a Tetra-Coordinated Lattice

Abstract

Strong magnetic coupling interactions originating from a short Mn−Mn distance in some heavy Mn 2+ -doped matrices have important effects on luminescence of single Mn 2+ ions and close-knit Mn 2+ −Mn 2+ pairs. However, the intrinsic mechanism of controlling spectral regulation remains elusive since the underlying relationship among Mn−Mn distances, magnetic coupling interactions, and optical properties is unclear. Herein, we create an unusual red emission (620 nm) of Mn 2+ in a typical tetracoordinated lattice of Li 2 CdGeO 4 by simply enhancing the Mn 2+doped level in addition to regular green emission (528 nm). Although the dual emission peaks occupy the same tetracoordinated crystallographic lattice of CdO 4 , different temperature-dependent emission behaviors are observed, which expands a possibility in optical thermometry sensors. Detailed Mn−Mn distances are calculated via Rietveld refinement analysis, and their effects on the Mn−Mn coupling interactions are evaluated. Furthermore, the Mn−Mn coupling interaction types are identified through electron spin resonance and magnetic measurements. The continuously decreasing distances between Mn 2+ ions strengthen the dipole−dipole coupling effect, resulting in the atypical red emission in a tetra-coordinated lattice environment. These findings elucidate the spectral regulation mechanism from the perspective of magnetic coupling interactions, providing a new pathway to regulate Mn 2+ -related emission.