Phase-formations of Mg2P2O7–Mn2P2O7 mixed pyrophosphates and their desired luminescence abilities

Abstract

In this work, a series of mixed pyrophosphates (Mg_1−xMn_x)₂P₂O₇ (x = 0–1.0) were prepared for the first time using a solid-state reaction method, which exhibits two kinds of structural variants, that is, α-(low temperature) and β-(high temperature) phases. The detailed phase-formations were determined via structural Rietveld refinements and the luminescence transitions of ⁴T₁ → ⁶A₁ in Mn²⁺. The phase-formation of (Mg_1−xMn_x)₂P₂O₇ (x = 0–1.0) shows a strict dependence on Mn²⁺ doping contents in the lattices. (Mg_1−xMn_x)₂P₂O₇ has an α-Mg₂P₂O₇ phase when the Mn²⁺-doping concentration is lower than x ≤ 0.1. With an increase of Mn²⁺ substitution above 20 mol% (x = 0.2–1.0), (Mg_1−xMn_x)₂P₂O₇ presents only the β-phase even at room temperature, while (Mg_1−xMn_x)₂P₂O₇ (x = 0.15) shows a mixed formation of α- and β-Mg₂P₂O₇ phases. The crystallographic surrounding of the Mn²⁺ activators in different structures had a strict influence on the spectral profile, luminescence efficiency, and color centers. Interestingly, in this series of phosphors, (Mg_1−xMn_x)₂P₂O₇ (x = 0.15) with the mixed phases of α- and β-type has overwhelming luminescence abilities such as the best luminescence intensity and high thermal stability. The pyrophosphates were confirmed to qualify for red-emitting LED lamps.