Enhancement of the Luminescent Properties of a New Red-Emitting Phosphor, Mn₂(HPO₃)F₂, by Zn Substitution

The Mn₂(HPO₃)­F₂ phase has been synthesized as single crystals by using mild hydrothermal conditions. The compound crystallizes in the orthorhombic Pnma space group, with unit cell parameters of a = 7.5607(8), b = 10.2342(7), and c = 5.5156(4) Å, with Z = 4. The crystal structure consists of a three-dimensional framework formed by alternating (010) layers of [MnO₃F₃] octahedra linked up by three connected [HPO₃] tetrahedra. Luminescence measurements were performed at different temperatures between 10 and 150 K. The 10 K emission spectrum of the octahedrally coordinated Mn­(II) cation exhibits a broad band centered at around 615 nm corresponding to the ⁴T₁ → ⁶A₁ transition. In order to explore the effect of the Mn­(II) concentration and the possibility of enhancing the luminescence properties of the Mn­(II) cation in Mn₂(HPO₃)­F₂, different intermediate composition members of the finite solid solution with the general formula (Mn_xZn_1–x)₂(HPO₃)­F₂ were prepared and their luminescent properties studied. The magnetic and specific heat behavior of M₂(HPO₃)­F₂ (M = Mn, Fe) have also been investigated. The compounds exhibit a global antiferromagnetic ordering with a spin canting phenomenon detected at approximately 30 K. The specific heat measurements show sharp λ-type peaks at 29.7 and 33.5 K for manganese and iron compounds, respectively. The total magnetic entropy is consistent with spin S = 5/2 and S = 2 of Mn­(II) and Fe­(II) cations.