Smart optical composite materials suitable for ratiometric sensing applications and harvesting options have been developed. The hybrid materials consist of core/shell particles with Fe3O4/SiO2 as the core and different luminescent lanthanide-containing metal–organic frameworks (MOFs) as the shell. The magnetic properties enable collection of microparticles via an external magnetic field and, thus, a strong signal augmentation of the luminescence signal. Thereby, MOF luminescence functions as a read-out signal of the sensing that can be influenced by different chemical compounds, e.g. by quenching with low concentrations of water. The combination of MOFs, which contain different luminescence centers combined with a different sensitivity towards water, results in a system that can be exploited as a ratiometric sensor. We have utilized the MOFs 3∞[Eu2(BDC)3]·2H2O·2DMF (BDC2− = benzene dicarboxylate) and 2∞[Ln2Cl6(bipy)3]·2bipy (Ln = Eu, Tb; bipy = 4,4′-bipyridine) for functionalization of the microparticles, resulting in a color-tuned yellow-emitting mixed-MOF composite system together with a Fe3O4/SiO2 core. Interaction with water decreases the luminescence unequally for both luminescence centers, which enables a quantitative determination of the water content by analysis of the ratio of the Tb3+ and Eu3+ luminescence bands. This process is supported by possible harvesting via superparamagnetism of the composite. Altogether, high sensitivity with a detection limit of 0.3% (20 μg) is achieved, equal to Karl-Fischer titration but also suitable for an “on-the-fly” analysis

Novel sensor particles have been developed that expand the variety of today's mechanochromic systems. The developed supraparticles consist of several different components to enable the sensor function. First, a luminescence-quenching core material is coated with silica nanoparticles. Second, this structure is surrounded by raspberry-like nanostructured silica particles, which host luminophore moieties. Upon shear stress, components spatially separated in the original supraparticles, namely quencher and luminophore components, come into contact. This causes an irreversible quenching of the luminescence (sensor turn-off ). Different options to select core, quencher, and luminophore components allow to drive the sensors to different sensing options regarding response time, sensitivity, and operation time. The sensors can be sensitive and rapid in response or generated to monitor the influence of shear stress over longer periods of time. Thus, a rapid, visible, "on-the-fly" sensing of shear stress is possible as well as monitoring the impact of prolonged shear stress. The particles are assembled by spray-drying. This affords flexibility when choosing the type of quencher and luminophore moiety. As such, the sensitivity of this robust, particle-based shear stress sensor system can be deliberately configured. Furthermore, the supraparticle sensor can be integrated in surfaces to create interactive, communicating materials.

A multi-component particle system was developed that combines the properties of white color, white light emission and strong magnetism on the macroscopic and microscopic scale. The system is constituted by...

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