Switchable Dual Emission of Luminescent Metal–Organic Framework@Nanoparticle Composites of EuBDC and ZrO‐Containing Hybrid Materials

For the preparation of luminescent materials with dual emission that combine two different luminescence processes with reversible switchability, the Eu$^{3+}$-containing metal–organic framework (MOF)$^3$∞[Eu$_2$(BDC)$_3$]·2DMF·2H$_2$O (EuBDC) (BDC = benzene dicarboxylate) was combined with zirconyl-containing nanoparticles ZrO(FMN) (FMN = flavin mononucleotide) and ZrO(MFP) (MFP = methyl fluoresceinphosphate), respectively. The resulting composite materials form dispersions in various media and combine the green luminescence of the nanoparticles with the red luminescence of the Eu$^{3+}$-containing MOF. Switching between the different chromaticities is enabled without a chemical transformation of the emitter but by variation of the excitation wavelength, as the emission processes of the two composite components exhibit different excitation wavelengths. While the FMN-containing composite particles own a red/green luminescence, the chromaticity of the MFP-containing system is further influenced by a strong solvatochromic effect of the nanoparticles. Therefore, further luminescence colors that comprise a large part of the visible spectrum can be generated in dependence of the solvent/dispersion media.