Tunable multi-color luminescence and white emission in lanthanide ion functionalized polyoxometalate-based metal–organic frameworks hybrids and fabricated thin films

In this paper, luminescent hybrid material systems are prepared with porous polyoxometalate-based metal–organic framework (POM-based MOF)[La(H₂O)₄(pdc)]₄}[SiMo₁₂O₄₀]·2H₂O (1) through the introduction of lanthanide ions (Ln³⁺, Ln = Eu, Tb, Sm, Dy, Eu/Tb, Dy/Eu) by a solvothermal approach. The POM-based MOF serves as a host for protecting the luminescence of Ln³⁺ cations. The structure, thermal stability, ultraviolet absorption and visible light emission of the target hybrid materials are determined with powder X-rays diffraction patterns (PXRD), Fourier transform infrared spectra (FTIR), thermalgravimetric analysis (TGA), inductively coupled plasma-mass spectrometry (ICP-MS) analysis, energy dispersive spectrometer (EDS), ultraviolet visible diffusion reflections spectra (UV–vis DRS) and especially luminescence spectra. The final luminescence of the Ln³⁺ hybrids can be adjusted by changing the composition of Ln³⁺ cations or converting the excitation wavelengths of them. Among [La_0.95Dy_0.045Eu_0.005(H₂O)₄(pdc)]₄}[SiMo₁₂O₄₀]·2H₂O (Dy³⁺/Eu³⁺@1) emits white luminescence under the excitation at 295 nm and the Commission Internationale de L'Eclairage (CIE) chromaticity coordinate of it is (0.361, 0.3408). Moreover, we manufacture POM-based MOF thin films by using ethyl methacrylate (EMA) to assemble the POM-based MOF on a quartz plate as substrate. The hybrid thin films based on {La_0.95Eu_0.05(H₂O)₄(pdc)]₄}[SiMo₁₂O₄₀]·2H₂O (Eu³⁺@1) and La_0.95Eu_0.04Tb_0.01(H₂O)₄(pdc)]₄}[SiMo₁₂O₄₀]·2H₂O (Eu³⁺/Tb³⁺ @1) can also achieve white-light. The CIE chromaticity coordinates of them are (0.3425, 0.2548) and (0.3857, 0.3377), respectively.