By using a layer‐by‐layer (LbL) approach, lanthanide‐based, monolithic metal–organic framework (MOF) thin films are fabricated for optical applications. In particular, the LbL approach allows manufacturing of heteroepitaxial Tb(III)‐Eu(III)(BTC) coatings with precise thickness control. Adjusting the Tb(III)‐to‐Eu(III) ratio allows tuning of the emission color. The hetero‐multilayer architecture makes it possible to suppress the direct Tb(III)‐to‐Eu(III) energy transfer, an unwanted phenomenon present in the corresponding mixed‐metal bulk MOF structures. The resulting Ln‐MOF thin films, or Ln‐surface‐anchored MOFs (SURMOFs), are characterized by X‐ray diffraction, infra‐red reflection absorption spectroscopy, UV–vis, and photoluminescence measurements. The results demonstrate that the heteroepitaxial SURMOF architectures carry huge potential for fabricating optical coatings for a wide range of applications.

Metal-organic frameworks (MOFs) are a class of crystalline porous coordination materials, which are assembled from inorganic nodes and organic linkers. Numerous applications, such as gas storage, molecule separation, catalysis, optical sensing, and charge transport, benefit from the outstanding properties of MOF materials. More advanced applications, e.g., in the electronics and optoelectronics area, demand homogeneous and monolithic MOF thin films. Recent studies demonstrated that surface-mounted MOFs (SURMOFs) are well suited to fulfill the requirements for the integration of MOFs into devices. As a crystalline thin-film material with tunable thickness, SURMOFs have been widely used in the optimization of chromophore stacking, electrical transport, stimuli-response, etc. The fabrication of SURMOFs is carried out employing a layer-by-layer (LbL) assembly technique, and it can yield MOF thin films with a well-defined orientation, tunable thickness, and editable crystalline heterostructure. We summarize the LbL assembly methods for SURMOF fabrication and the realization of advanced SURMOF architectures, including optical and electronic applications as well as the integration of photoactive SURMOFs and SURMOF-derived materials in technical devices. We conclude with a discussion of the challenges and prediction of the future of SURMOF materials.

The prolific topic of development of solidstate lighting devices has focused over the last years on solid-state white light (SSWL) emitting materials, mainly due the long operation lifetime and excellent harvesting and saving energy. [1] Even today, incandescent and mercury-based fluorescent materials are employed as white-light sources due to their superior warm-white light impression. Moreover, the fabrication of environmentally safe white light-emitting diode (LEDs) with a "warm-white" impression remains still a challenge. Many of the "white" organic light-emitting diode/ LED materials cover only part of the visible spectrum and lack the required efficacy of 150-200 lm W −1 for white-light performance. [2] For this reason, the design of a new generation of SSWL materials is of continuous interest in materials science, especially in areas such as full-color flat-panel electroluminescent displays for mobile devices, optical telecommunications, lighting, and backlighting for liquid-crystals displays. [3] Besides, high-quality white-light performance requires the Commission International de l'Eclairage (CIE) x,y coordinates 0.333, 0.333, with a correlated color temperature (CCT) into the 2500-6500 K, and color rendering index above 80 which are standard requirements for lighting applications. [4] One of the explored strategies to obtain white light is by combining red, green, and blue (RGB) sources to cover the visible region (400-700 nm) in the electromagnetic spectrum. [5] Also, metal-organic frameworks (MOFs) have been the focus of interest due to their potential applications in gas storage/ separation , [6] catalysis, [7] optics, [8] magnetism, [9] sensing, [10] and biomedicine. [4,11,12] Due to a permanent porosity, structural diversity, functionalization capabilities and then, tunable luminescence, MOF possess interesting properties for the development of SSWL composites. In recent years, a large number of luminescent MOFs have been reported for this purpose. [5,13-24] Moreover, for uses in nanotechnology, it is mandatory that MOFs are anchored on solid substrates, being particularly evident in the case of optoelectronic applications. [25,26] According to specialized reviews such as those from Wöll group, [27] it is distinguishable the surface-supported metal-organic frameworks (SURMOFs) devices, fabricated using layer-by-layer (LbL) A new set of Ln-MOF (lanthanide-metal-organic framework) thin films, known as Ln-SURMOFs (surface-supported MOFs), is fabricated with a layer-by-layer, in order to generate solid-state white-lighting devices. A three-component approach is carried out for a rational combination of red, green, and blue (RGB) emitting Eu 3+ , Tb 3+ , and Gd 3+ containing layers in order to achieve white-light emission. The Ln-SURMOFs are fully characterized by powder X-ray diffraction, infrared reflection-absorption spectroscopy, scanning electron microscopy, and photoluminescence spectroscopy (excitationemission and chromaticity determination according to Commission International de l'Eclairage, C...

Lanthanide-based crystalline coatings have a great potential for energy-conversion devices, but until now luminescent surface-anchored materials were difficult to fabricate. Thin films, called lanthanides surface-mounted metal–organic frameworks (SURMOFs) with tetrasubstituted halide (fluorine, chlorine, and bromine) terephthalic acid derivative linkers as a basic platform for optical devices, exhibit a high quantum yield of fluorescence visible to the naked eyes under ambient light. We show that we can tune the luminescent properties in thin films by halide substitution, which affords control over the molecular structure of the material. We rationalize the mechanism for the modulation of the photophysical properties by “antenna effect”, which controls the energy transfer and quantum yields using experimental and theoretical techniques for chelated lanthanides as a function of the type of atom substitutions at the phenyl rings and the resulting dihedral angle between phenyl rings in the linkers and carboxylate groups.

For the first time, a procedure has been established for the growth of surface-anchored metal–organic framework (SURMOF) copper(II) benzene-1,4-dicarboxylate (Cu-BDC) thin films of thickness control with single molecule accuracy. For this, we exploit the novel method solution atomic layer deposition (sALD). The sALD growth rate has been determined at 4.5 Å per cycle. The compact and dense SURMOF films grown at room temperature by sALD possess a vastly superior film thickness uniformity than those deposited by conventional solution-based techniques, such as dipping and spraying while featuring clear crystallinity from 100 nm thickness. The highly controlled layer-by-layer growth mechanism of sALD proves crucial to prevent unwanted side reactions such as Ostwald ripening or detrimental island growth, ensuring continuous Cu-BDC film coverage. This successful demonstration of sALD-grown compact continuous Cu-BDC SURMOF films is a paradigm change and provides a key advancement enabling a multitude of applications that require continuous and ultrathin coatings while maintaining tight film thickness specifications, which were previously unattainable with conventional solution-based growth methods.

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Seven isomorphous lanthanide metal–organic frameworks with special luminescence and magnetic properties are synthesized and characterized.

A stable porous MOF with a controllable particle size can be used as an HPLC situational phase for small organic molecule separations.