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.