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Luminomagnetic composites have been synthesized that allow for an individual tuning of luminescence intensity, chromaticity and magnetization by combination of superparamagnetic, citrate-stabilized iron oxide nanoparticles with the luminescent MOFs 3∞[Ln2(BDC)3(H2O)4] (Ln=Eu, Tb; BDC2-=terephthalate). The components are arranged to a concept of inverse structuring compared to previous luminomagnetic composites with MOF@magnetic particle (shell@core) composition so that the luminescent MOF now acts as core and is covered by magnetic nanoparticles forming the satellite shell. Thereby, the magnetic and photophysical properties are individually tuneable between high emission intensity (1.2 ⋅ 106 cps mg-1) plus low saturation magnetization (6 emu g-1) and the direct opposite (0.09 ⋅ 106 cps mg-1; 42 emu g-1) by adjusting the particle coverage of the MOF. This is not achievable with a core-shell structure having a magnetic core and a dense MOF shell. The composition of the composites and the influence of different synthesis conditions on their properties were investigated by SEM/EDX, PXRD, magnetization measurements and photoluminescence spectroscopy.

Herein, we report on the successful creation of a luminescent micron-sized magnet. A spray-drying approach was employed to do ""chemistry in a droplet"" in order to achieve opto-magnetic hybrids in form of micron-scaled particles in a fast and easy way in a single step. This is possible by combining preformed nanoparticles, rare earth metal salts and organic precursors, ultimately leading to nucleation and crystallization of a crystalline lanthanide-based metal-organic framework (MOFs) entangled with the preformed ferromagnetic iron oxide nanoparticles (FIONs). Overall, a truly entangled and stable hybrid is obtained, which combines magnetic and optical properties simultaneously (luminescent magnet) and allows for a completely free choice of the ratios of the constituents and thus flexible and stepless property tuning. On the one hand, the material system that is exemplarily shown herein exhibits very interesting properties. On the other hand, the synthesis and assembly strategy serve as an example for various and more exotic property combinations that can easily be achieved and provides a new generation of truly tunable hybrids, which can be perfectly designed for use in many applications.