Determination of phase-formation of (Mg1-xMnx)(2)Al4Si5O18(x=0-1) cordierite solid-solutionsviacrystallographic sites and luminescence dynamics of Mn(2+)centers

摘要

Aluminosilicate with the cordierite structure (Mg2Al4Si5O18) represents a big family of technologically important compounds with typical alpha- and beta-phases. Crystallographic sites for transition metal and rare earth ions in the cordierite structure have always been a controversial topic. In this work, the (Mg1-xMnx)(2)Al4Si5O18(x= 0-1.0) solid solution is firstly confirmedviaRietveld 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. (Mg1-xMnx)(2)Al4Si5O18(x= 0-1.0) undergoes structural changes from the orthorhombic beta-phase (x= 0-0.2), alpha-phase (x= 0.3-0.9) and Mn-cordierite (x= 0.95-1.0) (isostructural to beta-phase). It is technically meaningful that high-temperature alpha-phase cordierite Mg(2)Al(4)Si(5)O(18)can be stabilizedviaMn(2+)-doping (30-90 mol%). The crystallographic site-occupation of Mn(2+)activators is clearly identified. Interestingly, (Mg1-xMnx)(2)Al4Si5O18(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 beta-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 Mn(2+)for the octahedral Mg(2+)site in the cordierite lattices. The luminescence mechanism of Mn(2+)in (Mg1-xMnx)(2)Al(4)Si(5)O(18)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.