title: Smart Optical Composite Materials: Dispersions of Metal-Organic Framework@Superparamagnetic Microrods for Switchable Isotropic-Anisotropic Optical Properties.
abstract: A smart optical composite material with dynamic isotropic and anisotropic optical properties by combination of luminescence and high reflectivity was developed. This combination enables switching between luminescence and angle-dependent reflectivity by changing the applied wavelength of light. The composite is formed as anisotropic core/shell particles by coating superparamagnetic iron oxide-silica microrods with a layer of the luminescent metal-organic framework (MOF)3∞[Eu2(BDC)3]·2DMF·2H2O (BDC2-= 1,4-benzenedicarboxylate). The composite particles can be rotated by an external magnet. Their anisotropic shape causes changes in the reflectivity and diffraction of light depending on the orientation of the composite particle. These rotation-dependent optical properties are complemented by an isotropic luminescence resulting from the MOF shell. If illuminated by UV light, the particles exhibit isotropic luminescence while the same sample shows anisotropic optical properties when illuminated with visible light. In addition to direct switching, the optical properties can be tailored continuously between isotropic red emission and anisotropic reflection of light if the illuminating light is tuned through fractions of both UV and visible light. The integration and control of light emission modes within a homogeneous particle dispersion marks a smart optical material, addressing fundamental directions for research on switchable multifunctional materials. The material can function as an optic compass or could be used as an optic shutter that can be switched by a magnetic field, e.g., for an intensity control for waveguides in the visible range.
authors.affiliation: Fraunhofer Institute for Silicate Research, ISC , Neunerplatz 2, D97082 Würzburg, Germany.|Chair of Chemical Technology of Materials Synthesis, Julius-Maximilians-University Würzburg , Röntgenring 11, D97070 Würzburg, Germany.
authors.forename: Karl
authors.identifier: 0000-0002-1445-0702
authors.initials: K
authors.lastname: Mandel
authors.affiliation: Chair of Chemical Technology of Materials Synthesis, Julius-Maximilians-University Würzburg , Röntgenring 11, D97070 Würzburg, Germany.
authors.forename: Tim
authors.initials: T
authors.lastname: Granath
authors.affiliation: Institute of Inorganic Chemistry, Julius-Maximilians-University Würzburg , Am Hubland, 97074 Würzburg, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Wehner
authors.forename: Marcel
authors.initials: M
authors.lastname: Rey
authors.affiliation: Fraunhofer Institute for Silicate Research, ISC , Neunerplatz 2, D97082 Würzburg, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Stracke
authors.forename: Nicolas
authors.initials: N
authors.lastname: Vogel
authors.affiliation: Fraunhofer Institute for Silicate Research, ISC , Neunerplatz 2, D97082 Würzburg, Germany.|Chair of Chemical Technology of Materials Synthesis, Julius-Maximilians-University Würzburg , Röntgenring 11, D97070 Würzburg, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Sextl
authors.affiliation: Institute of Inorganic Chemistry, Julius-Maximilians-University Würzburg , Am Hubland, 97074 Würzburg, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Müller-Buschbaum
keywords: anisotropy; composites; isotropy; magnetic actuation; metal organic frameworks; optical properties; smart materials; superparamagnetism; switching