Mn–Mn Dimers Induced Multimode Emitters in Mn2+-Activated AZn4(PO4)3 (A = K, Rb, and Cs) with Unique [Zn4PO12] Chains and [ZnOn] Groups

Mn²⁺-doped luminescent materials play a significant role in a variety of fields, including modern lighting, displays, and imaging. Mn²⁺ exhibits a broad and adjustable emission, hinging on the local environment of the crystal field and the interaction of the 3d⁵ electrons. However, it is still a challenge to realize the precise control of the emission of Mn²⁺ ions due to site-prior occupation in a specific lattice. Here, the formation of Mn-Mn dimers is proposed to be an effective strategy to design a novel red emission. Multimode emitters in Mn²⁺-activated AZn₄(PO₄)₃ (A = K, Rb, and Cs) with unique [Zn₄PO₁₂] chains and [ZnO_n] groups are observed to achieve regular green and unusual red emissions. KZn₄(PO₄)₃:Mn²⁺ shows broad dual emissions at 542 and 608 nm, attributed to [MnO₄] and [Mn₂O₇] dimers, respectively. While K is replaced with Rb and Cs, the Zn ions form [ZnO₄] tetrahedra and [ZnO₅] octahedra. RbZn₄(PO₄)₃:Mn²⁺ exhibits a broad red emission at 618 nm, ascribing to [Mn₂O₇] and [Mn₂O₈] dimers. CsZn₄(PO₄)₃:Mn²⁺ also displays a broad orange-red emission at 608-620 nm with increasing doping levels, deriving from energy transfer from [MnO₅] to [Mn₂O₇] and [Mn₂O₈] dimers. This work provides a framework for creating novel red emissions from Mn²⁺-doped luminescent materials.