Ratiometric nanothermometer based on an emissive Ln3+-organic framework

A micrometer-sized europium(iii)–organic framework for selective sensing of the Cr2O72− anion and picric acid in water systems

A micrometer-sized europium(iii)–organic framework with good dispersibility, excellent thermal and environmental stability, and easy regeneration ability can serve as a dual-responsive luminescent sensor to probe both Cr₂O₇²⁻ and picric acid contaminants in water system.

Lanthanide Organic Framework Luminescent Thermometers

Metal-organic frameworks (MOFs) are excellent platforms for engineering luminescence properties as their building blocks, metal ions, linkers, and guest ions or molecules, are all potential sources of light emission. Temperature is one of the most important physical properties affecting the dynamics and viability of natural and engineered systems. Because the luminescence of certain lanthanide-bearing MOFs changes considerably with temperature, in the last few years, these materials have been explored as optical thermometers, especially in temperature sensing based on the intensity ratios of two separate electronic transitions. This review discusses the main concepts and ideas assisting the design of such ratiometric thermometers, and identifies the main challenges presented to this nascent field: develop nanothermometers for bio-applications and nanomedicine; understand the energy transfer mechanisms determining the thermal sensitivity; achieve effective primary thermometers; realize multifunctional nanothermometers; integrate Ln³⁺ -based thermometers in commercial products.

Ratiometric Nanothermometer Based on Rhodamine Dye-Incorporated F127-Melamine-Formaldehyde Polymer Nanoparticle: Preparation, Characterization, Wide-Range Temperature Sensing, and Precise Intracellular Thermometry

A series of fluorescent nanothermometers (FTs) was prepared with Rhodamine dye-incorporated Pluronic F-127-melamine-formaldehyde composite polymer nanoparticles (R-F127-MF NPs). The highly soluble Rhodamine dye molecules were bound with Pluronic F127 micelles and subsequently incorporated in the cross-linked MF resin NPs during high-temperature cross-link treatment. The morphology and chemical structure of R-F127-MF NPs were characterized with dynamic light scattering, electron microscopy, and Fourier-transform infrared (FTIR) spectra. Fluorescence properties and thermoresponsivities were analyzed using fluorescence spectra. R-F127-MF NPs are found to be monodispersed, presenting a size range of 88-105 nm, and have bright fluorescence and high stability in severe treatments such as autoclave sterilization and lyophilization. By simultaneously incorporating Rhodamine B and Rhodamine 110 (as reference) dyes at a doping ratio of 1:400 in the NPs, ratiometric FTs with a high sensibility of 7.6%·°C(-1) and a wide temperature sensing range from -20 to 110 °C were obtained. The FTs exhibit good stability in solutions with varied pH, ionic strengths, and viscosities and have similar working curves in both intracellular and extracellular environments. Cellular temperature variations in Hela cells during microwave exposure were successfully monitored using the FTs, indicating their considerable potential applications in the biomedical field.

A highly sensitive near-infrared luminescent metal-organic framework thermometer in the physiological range

A near-infrared luminescent metal-organic framework Nd0.866Yb0.134BTB was developed as a self-calibrated thermometer in the physiological range. Its features include high sensitivity and resolution, and good biocompatibility, making such a material useful for biomedical applications.

Chemical Sensors Based on Metal-Organic Frameworks

Metal-organic frameworks (MOFs) as chemical sensors have developed rapidly in recent years. There have been many papers concerning this field and interest is still growing. The reason is that the specific merits of MOFs can be utilized to enhance sensitivity and selectivity by various energy/charge transfers occurring among different ligands, ligand, and metal centers, such as from ligands to metal centers or metal centers to ligands, as well as from MOF skeletons to guest species. This review intends to provide an update on recent progress in various applications of different MOF-based sensors on the basis of their luminescent and electrochemical responses towards small molecules, gas molecules, ions (cations and anions), pH, humidity, temperature, and biomolecules. MOF-based sensors function by utilizing different mechanisms, including luminescent responses of "turn-on" and "turn-off", as well as electrochemical responses.

Photonic hybrid crystals constructed from in situ host-guest nanoconfinement of a light-emitting complex in metal-organic framework pores

We report the concept underpinning the facile nanoconfinement of a bulky luminous guest molecule in the pores of a metal-organic framework (MOF) host, which yields a hybrid host ⊃ guest nanomaterial with tunable opto-electronic characteristics and enhanced photostability. Utilizing an in situ host-guest confinement strategy enabled by molecular self-assembly, we show that the highly emitting ZnQ [Zn-(bis-8-hydroxyquinoline)] guest complexes could be rapidly encapsulated within the sodalite nanocages of zeolitic imidazolate framework (ZIF-8) host crystals. The nature of optical and electronic transitions phenomena of the guest-encapsulated ZIF-8 ⊃ ZnQ has been elucidated by means of fluorescence and absorption spectroscopy measurements, and substantiated further via theoretical molecular orbital calculations revealing the plausible host-guest charge transfer mechanism involved. Evidence suggests that its photophysical properties are not only strongly determined by the host-guest co-operative bonding interactions within the environment of the confined MOF nanocage, but also can be engineered to manipulate its emission color chromaticity or to shield light-sensitive emitting guests against rapid photochemical degradation.

Controllable synthesis of Zn/Cd(ii) coordination polymers: dual-emissive luminescent properties, and tailoring emission tendency under varying excitation energies

With the help of rationally selected N-donor ligands, different dimensional architectures 1–5 have been synthesized and they display dual-emission properties.

A dye encapsulated terbium-based metal–organic framework for ratiometric temperature sensing

A ratiometric and colorimetric thermometer with high sensitivity and significant color change from 50 to 300 K has been developed by encapsulating the luminescent dye 7-diethylamino-4-methylcoumarin (C460) into the channels of a terbium-based MOFTbTATAB.

Nd³⁺-sensitized NaLuF₄ luminescent nanoparticles for multimodal imaging and temperature sensing under 808 nm excitation

In this paper, intense up- and down-conversion luminescence were successfully achieved in well designed and synthesized core-shell structured NaLuF4:Gd/Yb/Er@NaLuF4:Yb@NaLuF4:Nd/Yb@NaLuF4 nanoparticles (NPs) simultaneously under 808 nm continuous-wave laser excitation. The morphologies, luminescent properties and energy transfer mechanism of the nanoparticles were studied in detail. By employing this design, multimodal imaging performance including near-infrared down-conversion optical imaging and X-ray computed tomography (CT) imaging were realized in one kind of NPs. Furthermore, the 808 nm excited optical temperature sensing property of the synthesized NPs was realized in a wide temperature range by monitoring the intensities of up- and down-conversion luminescence. This study provides a novel platform based on lanthanide fluoride nanoparticles for multifunctional imaging and temperature sensing in one system.

α-NaYb(Mn)F4:Er(3+)/Tm(3+)@NaYF4 UCNPs as "Band-Shape" Luminescent Nanothermometers over a Wide Temperature Range

Novel flower-like α-NaYb(Mn)F4:Er(3+)/Tm(3+)@NaYF4 upconversion nanoparticles (UCNPs) as luminescent nanothermometers have been developed by combining liquid-solid solution hydrothermal strategy with thermal decomposition strategy. Under 980 nm excitation, they exhibit intense upconversion luminescence and temperature-dependent upconversion luminescence over a wide temperature range. The influence of temperature on "band-shape" upconversion luminescence (UCL) spectra and the intensity of emission bands are analyzed and discussed in detail. We further successfully test and verify that intensity ratios REr of (2)H11/2 → (4)I15/2 and (4)S3/2 → (4)I15/2 and RTm of (1)G4 → (3)H5 and (3)H4 → (3)H6 are sensitive to temperature, and the population of active ions follows Boltzmann-type population distribution very well. These luminescent nanothermometers could be applied over a wide temperature range from 123 to 423 K with high sensitivity, which enable them to be excellent candidates for temperature sensors.

Metal-Organic Frameworks as Chemical Sensors

Chemical sensing is of critical importance in today's society in a variety of applications from medicine to environmental pollution control, and from food safety monitoring to the detection of illicit substances and chemical weapons. Metal–organic frameworks (MOFs) have shown tremendous promise as a new class of chemical sensor materials that could be integrated into future devices. MOFs are microporous crystalline materials with infinite, periodic structures composed of organic ‘linkers’ connected to metal ‘nodes’. Their architectures can be fine-tuned by synthetic design for task-specific purposes: as chemical sensors, MOFs can be designed to interact with specific target analytes. Interest in MOFs as chemical sensors has grown significantly over the last decade, particularly given the increasing number of examples of luminescent lanthanide-based MOFs, and MOFs that display mechanochemical responses to external stimuli. In this chapter, we discuss some of the fundamental properties required to prepare MOFs for chemical sensing. We then present an extensive review of recent research in this area, showing how MOFs have been applied in a wide range of applications, including sensing of anions, cations, small organic molecules, biomolecules, as well as changes in physical conditions such as temperature and pH.

A Nanoscale Multiresponsive Luminescent Sensor Based on a Terbium(III) Metal-Organic Framework

A nanoscale terbium-containing metal-organic framework (nTbL), with a layer-like structure and [H2 NMe2 ](+) cations located in the framework channels, was synthesized under hydrothermal conditions. The structure of the as-prepared sample was systematically confirmed by powder XRD and elemental analysis; the morphology was characterized by field-emission SEM and TEM. The photoluminescence studies revealed that rod-like nTbL exhibited bright-green emission, corresponding to (5)D4 →(7)FJ (J=6-3) transitions of the Tb(3+) ion under excitation. Further sensing measurements revealed that as-prepared nTbL could be utilized as a multiresponsive luminescent sensor, which showed significant and exclusive detection ability for Fe(3+) ions and phenylmethanol. These results highlight the practical applications of lanthanide-containing metal-organic frameworks as fluorescent probes.

Lanthanides post-functionalized nanocrystalline metal-organic frameworks for tunable white-light emission and orthogonal multi-readout thermometry

We demonstrate tunable white-light emission and multi-readout thermometry in two respective nanocrystalline luminescent metal-organic frameworks (MOFs), which are prepared via postsynthetic functionalization with lanthanide cations of a robust UiO type MOF bearing the 2,2'-bipyridyl moiety (UiO-67-bpydc, 1). The white-light emitting framework Eu(3+)@1 can be conveniently applied as a thin film onto a commercial UV-LED chip for practical white lighting applications. The multi-readout orthogonal thermometry is illustrated in relation to the emission intensity ratio as well as the decay time and luminescence color of Eu(3+)/Tb(3+)@1 nanocrystals. This work highlights the opportunity for designing white-light emitters and nanothermometers based on lanthanide functionalized MOFs.

Dual-emitting MOF⊃dye composite for ratiometric temperature sensing

A strategy to achieve a ratiometric thermometer by encapsulating luminescent perylene dye into the pores of a europium metal-organic framework (MOF) is developed. The resulting MOF⊃dye thermometer exhibits highly temperature-dependent luminescence intensity ratio over the physiological temperature range, with a maximum sensitivity of 1.28% °C(-1) at 20 °C.

Fabrication of fluorescent SiO2@zeolitic imidazolate framework-8 nanosensor for Cu2+ detection

The formation of core–shell SiO₂@ZIF-8 nanostructures for Cu²⁺ detection is reported here.

Chemical stability and tunable luminescence of Ln(iii)–K(i) coordination polymers featuring a tracery-like architecture

With the help of in situ generation of sulfate anion, three Ln(iii)–K(i) sulfate and oxalate coordination polymers have been synthesized. These compounds display thermal and chemical stability, as well as good temperature and pH sensing ability.

A ketone functionalized luminescent terbium metal–organic framework for sensing of small molecules

A ketone functionalized luminescent terbium metal–organic framework has been realized for the highly selective and sensitive sensing of aniline.

Highly stable and sensitive LnMOF ratiometric thermometers constructed with mixed ligands

By introducing ancillary ligands into M'LnMOFs and removing coordinated water molecules from the inner coordination sphere, we have successfully realized two types of highly stable and sensitive thermometers that in addition exhibit brilliant luminescence over a wide temperature range, providing a new strategy to explore luminescence-based M'LnMOF thermometers.

Sustainable synthesis of a catalytic active one-dimensional lanthanide–organic coordination polymer

Rationalization of the synthetic conditions allowed the predictable fast sustainable preparation of [La₂(H₃nmp)₂(H₂O)₄]·4.5H₂O having a 1D coordination polymer.

Carbon dot grafted SrAl2O4:Eu,Dy dual-emitting phosphor for ratiometric temperature sensing

We incorporated carbon dots (CDs) into a SrAl₂O₄:Eu,Dy phosphor (SAO), and made use of the dual emission from the CDs and SAO within such a composite to realize ratiometric temperature sensing from 100 to 400 K.

Engineering lanthanide-optical centres in IRMOF-3 by post-synthetic modification

Infrared emitters based on IRMOF-3 are modified with 2-chloroacetic acid, glyoxylic acid, diethyl (ethoxymethylene)malonate, methyl vinyl ketone, and Eu³⁺& Nd³⁺.

Metal–organic frameworks for luminescence thermometry

We describe the recent progress made in luminescent MOF thermometers, and especially highlight the development of dual-emitting ratiometric thermometers.

A near infrared luminescent metal–organic framework for temperature sensing in the physiological range

A near infrared luminescent metal–organic framework thermometer Nd0.577Yb0.423BDC-F4 has been realized and shows excellent sensitivity in the physiological temperature range.

An organic-ligand-free thermochromic luminescent cuprous iodide trinuclear cluster: evidence for cluster centered emission and configuration distortion with temperature

An organic-ligand-free cuprous iodide trinuclear cluster with significant temperature-dependent structural distortion shows thermochromic luminescence originating from a single cluster-centered triplet.

Lanthanide-doped NaGdF4 core-shell nanoparticles for non-contact self-referencing temperature sensors

We report that non-contact self-referencing temperature sensors can be realized with the use of core-shell nanostructures. These lanthanide-based nanothermometers (NaGdF4:Yb(3+)/Tm(3+)@Tb(3+)/Eu(3+)) exhibit higher sensitivity in a wide range from 125 to 300 K based on two emissions of Tb(3+) at 545 nm and Eu(3+) at 615 nm under near-infrared laser excitation.