Determination of phase-formation of (Mg1−xMnx)2Al4Si5O18 (x = 0–1) cordierite solid-solutions via crystallographic sites and luminescence dynamics of Mn2+ centers

Abstract

Aluminosilicate with the cordierite structure (Mg₂Al₄Si₅O₁₈) represents a big family of technologically important compounds with typical α- and β-phases. Crystallographic sites for transition metal and rare earth ions in the cordierite structure have always been a controversial topic. In this work, the (Mg_1−xMn_x)₂Al₄Si₅O₁₈ (x = 0–1.0) solid solution is firstly confirmed via Rietveld structural refinements and luminescence dynamics. The well-crystallized ceramics were prepared by high-temperature solid-state reaction, and then characterized using structural, morphological, luminescence, decays, and thermal quenching measurements. (Mg_1−xMn_x)₂Al₄Si₅O₁₈ (x = 0–1.0) undergoes structural changes from the orthorhombic β-phase (x = 0–0.2), α-phase (x = 0.3–0.9) and Mn-cordierite (x = 0.95–1.0) (isostructural to β-phase). It is technically meaningful that high-temperature α-phase cordierite Mg₂Al₄Si₅O₁₈ can be stabilized via Mn²⁺-doping (30–90 mol%). The crystallographic site-occupation of Mn²⁺ activators is clearly identified. Interestingly, (Mg_1−xMn_x)₂Al₄Si₅O₁₈ (x = 0.01–1.0) presents tunable colors produced by two distinct luminescence centers, that is, green Mn²⁺(A) and red Mn²⁺(B) bands centered at about 530 and 650 nm, respectively. The most efficient excitation wavelengths and decay times of Mn²⁺(A) are distinct from those of Mn²⁺(B). The Mn²⁺(A) green centers are only observed in β-phase cordierite (x = 0.01–0.2) with a dominant emission intensity compared with Mn²⁺(B), while the Mn²⁺(B) red centers are observed in all samples (x = 0.01–1.0). The Mn²⁺(A) center fills in the hexagonal channels, while Mn²⁺(B) is related to the substitution of Mn²⁺ for the octahedral Mg²⁺ site in the cordierite lattices. The luminescence mechanism of Mn²⁺ in (Mg_1−xMn_x)₂Al₄Si₅O₁₈ was proposed. The results can be used for basic and application research studies in a wide family of rare earth or transition-metal-doped cordierite materials.