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Metal-organic framework luminescence in the yellow gap by codoping of the homoleptic imidazolate 3[Ba(Im)2] with divalent europium

: Rybak, Jens-Christoph; Hailmann, Michael; Matthes, Philipp R.; Zurawski, Alexander; Nitsch, Jörn; Steffen, Andreas; Heck, Joachim G.; Feldmann, Claus; Götzendörfer, Stefan; Meinhardt, Jürgen; Sextl, Gerhard; Kohlmann, Holger; Sedlmaier, Stefan J.; Schnick, Wolfgang; Müller-Buschbaum, Klaus


Journal of the American Chemical Society 135 (2013), Nr.18, S.6896-6902
ISSN: 0002-7863
ISSN: 1520-5126
Fraunhofer ISC ()

The rare case of a metal-triggered broad-band yellow emitter among inorganic-organic hybrid materials was achieved by in situ codoping of the novel imidazolate metal-organic framework 3[Ba(Im)2] with divalent europium. The emission maximum of this dense framework is in the center of the yellow gap of primary light-emitting diode phosphors. Up to 20% Eu2+ can be added to replace Ba2+ as connectivity centers without causing observable phase segregation. High-resolution energy-dispersive X-ray spectroscopy showed that incorporation of even 30% Eu2+ is possible on an atomic level, with 2-10% Eu2+ giving the peak quantum efficiency (QE = 0.32). The yellow emission can be triggered by two processes: direct excitation of Eu2+ and an antenna effect of the imidazolate linkers. The emission is fully europium-centered, involving 5d ? 4f transitions, and depends on the imidazolate surroundings of the metal ions. The framework can be obtained by a solvent-free in situ approach starting from barium metal, europium metal, and a melt of imidazole in a redox reaction. Better homogeneity for the distribution of the luminescence centers was achieved by utilizing the hydrides BaH2 and EuH2 instead of the metals.