Metal–organic frameworks (MOFs) display a wide range of luminescent behaviors resulting from the multifaceted nature of their structure. In this critical review we discuss the origins of MOF luminosity, which include the linker, the coordinated metal ions, antenna effects, excimer and exciplex formation, and guest molecules. The literature describing these effects is comprehensively surveyed, including a categorization of each report according to the type of luminescence observed. Finally, we discuss potential applications of luminescent MOFs. This review will be of interest to researchers and synthetic chemists attempting to design luminescent MOFs, and those engaged in the extension of MOFs to applications such as chemical, biological, and radiation detection, medical imaging, and electro-optical devices (141 references).

Luminescent Metal–Organic Frameworks

Lanthanide-based luminescent hybrid materials.

Interpretation of europium(III) spectra

Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Advanced oxidation processes (AOPs), defined as those technologies that utilize the hydroxyl radical (·OH) for oxidation, have received increasing attention in the research and development of wastewater treatment technologies in the last decades. These processes have been applied successfully for the removal or degradation of toxic pollutants or used as pretreatment to convert recalcitrant pollutants into biodegradable compounds that can then be treated by conventional biological methods. The efficacy of AOPs depends on the generation of reactive free radicals, the most important of which is the hydroxyl radical (·OH). The authors summarize the formation reactions of ·OH and the mechanisms of pollutants degradation. They cover six types of advanced oxidation processes, including radiation, photolysis and photocatalysis, sonolysis, electrochemical oxidation technologies, Fenton-based reactions, and ozone-based processes. Controversial issues in pollutants degradation mechanism were discussed. They review t...

Advanced Oxidation Processes for Wastewater Treatment: Formation of Hydroxyl Radical and Application

A new series of quaternary and ternary polymeric hybrid materials were assembled from 3-methacryloxypropyltrimethoxysilane (MS), methacrylic acid (MA), 1,10-phenanthroline (phen) and rare earth (Eu3+, Tb3+, and Dy3+) precursors. MS and MSMA (copolymer of MS and MA) behave as structural functional component to form the inorganic polymeric network or inorganic/organic polymeric host through the coordination to rare earth ions, while phen acts as the energy sensitizer for the luminescence of rare earth ions. Subsequently, six novel hybrid materials (phen–Eu(Tb, Dy)–MS, phen–Eu(Tb, Dy)–MSMA) were obtained, in which inorganic component is connected with polymer component through covalent bond. It was found that the introduction of organic polymer unit has influence on the microstructure and especially the luminescent properties of hybrid materials. The quantum efficiency of Eu hybrids was also studied. All these hybrids exhibit the characteristic luminescence of rare earth ions, which substantiates optimum energy match and effective intramolecular energy transfer between the triplet state energy of phen and emissive energy level of Eu3+, Tb3+ and Dy3+. It was worth pointing out that the quaternary hybrid materials (phen–Eu3+(Tb3+, Dy3+)–MSMA) with organic polymer unit (MA) present stronger luminescence intensities, longer lifetimes than those of ternary ones without MA (phen–Eu3+(Tb3+, Dy3+)–MS), suggesting the introduction of organic chain (MA) is beneficial for the photophysical property of hybrids.

Molecular assembly and photophysical properties of covalently bonded rare earth polymeric hybrid materials phen–RE–MSMA (MS)

Novel phosphors of Eu 3+ /Tb 3+ doped RE 3 BO 6 (RE = Y, Gd) have been prepared using an original modified in situ sol–gel synthesis route. Different optimized organic media were mixed with rare earth coordination polymers, and tri- n -butyl borate was added to assemble inorganic/organic multi-component hybrid precursors. After calcinations of the resulting precursors at 1000 °C, target phosphors were obtained. The microstructure and morphology information of the phosphors were investigated via the technique of X-ray powder diffraction (XRD) and scanning electronic microscopy, and it has been shown that these phosphors present symmetrical distribution and high packing density, whose grain sizes were around 200 nm. Analyzed by luminescent spectra, these phosphor particles show narrow lines of emissions respectively originating from their characteristic transitions, and the dominating emission peak is due to the hypersensitive transition. The RE 3 BO 6 : Eu 3+ /Tb 3+ (RE = Y, Gd) phosphors can be expected to gain more practical applications in commercial phosphors and other luminescent materials used in advanced devices.

Sol–gel synthesis and photoluminescence of RE3BO6: Eu3+/Tb3+ (RE = Y, Gd) microcrystalline phosphors from hybrid precursors

Through altering the solvents, we have obtained the Eu3+/Tb3+ ions-doped LnPO4 (Ln = La, Gd) phosphors with different particle sizes, microstructures and morphologies via a facile solvo-thermal technology. X-ray powder diffraction (XRD), transmission electron microscope (TEM), and scanning electron microscope (SEM) have shown that the products using different solvents have various structures and morphologies. With the increase of DMA/water volume ratio, the microstructure has changed from hexagonal phase to monoclinic one, and the morphology from nanorod to nanoparticle, revealing the decreased oriented growth. The presence of DMA is an important factor in guiding the anisotropic growth of hexagonal lanthanide phosphates. Besides, N-methyl-2-pyrrolidone has been used as solvent to induce the Eu3+/Tb3+ ions-doped LnPO4 (Ln = La, Gd) phosphors with different morphologies and structures. Finally, the photoluminescence behaviors of these nanocrystals have been investigated, which are dependent on their microstructures and morphologies.

LnPO4: RE3+ (La = La, Gd; RE = Eu, Tb) nanocrystals: solvo-thermal synthesis, microstructure and photoluminescence

Eu3+-doped oxy-phosphate (La3PO7:Eu3+) with monoclinic phase has been synthesized via solid phase and co-precipitation methods. The products present various regular morphologies after high temperature thermal treatment, such as bulk with holes, leaf-like flake, nano-rod and so on. All the phosphors exhibit the characteristic fluorescence of Eu ion, the electric dipole transition 5D0→7F2 of Eu3+ ions is dominant indicating that the sites of Eu3+ ions in La3PO7 have no the inversion center. Furthermore, the intensity of 5D0→7F2 increases due to the introducing of surfactant and increasing of the calcination temperature.

Controlled chemical co-precipitation and solid phase synthesis, microstructure and photoluminescence of La3PO7:Eu3+ phosphors

A series of ternary organic/inorganic/polymer hybrid materials have been assembled on the basis of the coordination chemistry principle. Mercapto-functionalized MBA-Si from MBA (4-mercaptobenzoic acid) behaves as the first coordination unit, which forms sulfide linkages, resulting in an inorganic Si-O network after hydrolysis and copolycondensation with TEOS (tetraethoxysilane). The organic polymers PVPD [poly(4-vinylpyridine)] and PMMA [poly(methyl methacrylate)] play a role of the second coordination unit, whose organic polymeric C-C chain originates from addition polymerization of the monomers 4-VPD (4-vinylpyridine) and MMA (methyl methacrylate), respectively. These hybrids are characterized in detail to compare with the binary hybrids without an organic polymer unit, whose results reveal that the microstructure, the thermal stability, and especially the photoluminescence properties of the hybrid system are improved with the introduction of the polymer as the coligand.

Ternary Rare Earth Inorganic–Organic Hybrids with a Mercapto‐Functionalized Si–O Linkage and a Polymer Chain: Coordination Bonding Assembly and Luminescence

Bing Yan

Papers

Molecular assembly and photophysical properties of covalently bonded rare earth polymeric hybrid materials phen–RE–MSMA (MS)

Sol–gel synthesis and photoluminescence of RE3BO6: Eu3+/Tb3+ (RE = Y, Gd) microcrystalline phosphors from hybrid precursors

LnPO4: RE3+ (La = La, Gd; RE = Eu, Tb) nanocrystals: solvo-thermal synthesis, microstructure and photoluminescence

Controlled chemical co-precipitation and solid phase synthesis, microstructure and photoluminescence of La3PO7:Eu3+ phosphors

Ternary Rare Earth Inorganic–Organic Hybrids with a Mercapto‐Functionalized Si–O Linkage and a Polymer Chain: Coordination Bonding Assembly and Luminescence