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Group (III) Nitrides M[Mg2Al2N4] (M = Ca, Sr, Ba, Eu) and Ba[Mg2Ga2N4]Structural Relation and Nontypical Luminescence Properties of Eu2+ Doped Samples

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posted on 11.11.2014, 00:00 by Philipp Pust, Frauke Hintze, Cora Hecht, Volker Weiler, Andreas Locher, Daniela Zitnanska, Sascha Harm, Detlef Wiechert, Peter J. Schmidt, Wolfgang Schnick
The isotypic nitridomagnesoaluminates M[Mg2Al2N4] (M = Ca,Sr, Ba,Eu) as well as a novel nitridomagnesogallate Ba­[Mg2Ga2N4] have been synthesized by high-temperature reactions in arc-welded tantalum ampules. The crystal structures were solved and refined using single-crystal X-ray diffraction or powder X-ray diffraction data, respectively. All compounds crystallize in the UCr4C4-structure type (space group I4/m (no. 87), Z = 2, Ca­[Mg2Al2N4]: a = 8.0655(11), c = 3.2857(7) Å, wR2 = 0.085 Sr­[Mg2Al2N4]: a = 8.1008(11), c = 3.3269(7) Å, wR2 = 0.084; Eu­[Mg2Al2N4]: a = 8.1539(12), c = 3.3430(7) Å, wR2 = 0.033; Ba­[Mg2Al2N4]: a = 8.2602(9), c = 3.43198(19) Å, wRp = 0.031; Ba­[Mg2Ga2N4]: a = 8.3654(12), c = 3.4411(7) Å, wR2 = 0.031) forming highly condensed anionic networks of disordered (Al/Mg)­N4 and (Ga/Mg)­N4 units, connected to each other by common edges and corners. The M2+ site is centered in vierer ring channels along [001] and coordinated in a cuboidal surrounding by N. Eu2+ doped samples of M[Mg2Al2N4] (M = Ca,Sr,Ba) exhibit nontypical luminescence properties including trapped exciton emission in the red spectral region. These compounds widen the group of novel red-emitting materials such as Ca­[LiAl3N4]:Eu2+, Sr­[LiAl3N4]:Eu2+, or Sr­[Mg3SiN4]:Eu2+. Therefore, deep discussion of the observed anomalous luminescence is essential to understand the correlations between all these materials, which are fundamental to design narrow band luminescence of Eu2+ systems.

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