Flexible and transparent films consisting of lanthanide complexes for ratiometric luminescence thermometry

Eu3+-Directed Supramolecular Metallogels with Reversible Quadruple-Stimuli Response Behaviors

Smart luminescent materials that have the ability to reversibly adapt to external environmental stimuli and possess a wide range of responses are continually emerging, which place higher demands on the means of regulation and response sites. Here, europium ions (Eu3+)-directed supramolecular metallogels are constructed by orthogonal self-assembly of Eu3+ based coordination interactions and hydrogen bonding. A new organic ligand (L) is synthesized, consisting of crown ethers and two flexible amide bonds-linked 1,10-phenanthroline moieties to coordinate with Eu3+. Synergistic intermolecular hydrogen bonding in L and Eu3+-L coordination bonding enable Eu3+ and L to self-assemble into shape-persistent 3D coordination metallogels in MeOH solution. The key to success is the utilization of crown ethers, playing dual roles of acting both as building blocks to build L with C2-symmetrical structure, and as the ideal monomer for increasing the energy transfer from L to Eu3+'s excited state, thus maintaining the excellent luminescence of metallogels. Interestingly, such assemblies show K+, pH, F-, and mechano-induced reversible gel-sol transitions and tunable luminescence properties. Above findings are useful in the studies of molecular switches, dynamic assemblies, and smart luminescent materials.

Lemon-derived carbon dots as antioxidant and light emitter in fluorescent films applied to nanothermometry

The design of luminescent nanomaterials for the development of nanothermometers with high sensitivity and free of potentially toxic metals has developed in several fields, such as optoelectronics, sensors, and bioimaging. In addition, luminescent nanothermometers have advantages related to non-invasive measurement, with their wide detection range and high spatial resolution at the nano/microscale. Our study is the first, to our knowledge, to demonstrate a detailed study of a fluorescent film (Film-L) thermal sensor based on carbon dots derived from lemon bagasse extract (CD-L). The CD-L properties were explored as an antioxidant agent; their cytotoxicity was evaluated by using a human non-tumoral skin fibroblast (HFF-1) cell line from an MTT assay. The CD-L were characterized by HRTEM, DLS, FTIR, UV-VIS, and fluorescence spectroscopy. These confirmed their particle size distribution below 10 nm, graphitic structure in the core and surface organic groups, and strong blue emission. The CD-L showed cytocompatibility behavior and scavenging potential reactive species of biological importance: O2•- and HOCl, with IC50 of 276.8 ± 4.0 and 21.6 ± 0.7, respectively. The Film-L emission intensities (I425 nm) are temperature-dependent in the 298 to 333 K range. The Film-L luminescent thermometer shows a maximum relative thermal sensitivity of 2.69 % K-1 at 333 K.

Double-Network Luminescent Films Constructed Using Sulfur Quantum Dots and Lanthanide Complexes

Although UV light-switchable luminescent films are of importance for application in soft optical devices and anticounterfeiting labels, there are still challenges in developing such films integrated with outstanding luminescent property, high self-healing efficiency, and simultaneously excellent mechanical strength. Herein, double-network (DN) luminescent films are designed and constructed via an intermolecular hydrogen bond crosslinking strategy of poly(ethylene glycol) (PEG) in sulfur quantum dots (S-QDs) and polyurethane (PU), where S-QDs ("stone" one) play dual roles of acting both as a soft segment to crosslink another segment PU ("bird" one) and also as the origin of a luminescence center ("bird" two) in films. In addition, lanthanide(III) complexes (LnCs, Ln═Eu³⁺, Tb³⁺) are employed as another emission source to embed in the films and switch the emission colors of DN films from the multicolor (red-yellow-green) of LnCs to the blue color of S-QDs by changing the ultraviolet excitation wavelength from 254 to 365 nm. It is worth noting that the crosslinking network strategy can effectively prevent S-QDs and LnCs from aggregating or leaking and enable both luminescence centers to homogeneously distribute, resulting in luminescent DN films possessing extraordinary UV light-switchable luminescence, improved mechanical property, and excellent self-healing ability. This work presents a viable method for the design and fabrication of luminescent films with multifunctional applications in flexible robotics, wearable devices, and dual-luminescent anticounterfeiting materials.

Overview of N-Rich Antennae Investigated in Lanthanide-Based Temperature Sensing

The market share of noncontact temperature sensors is expending due to fast technological and medical evolutions. In the wide variety of noncontact sensors, lanthanide-based temperature sensors stand out. They benefit from high photostability, relatively long decay times and high quantum yields. To circumvent their low molar light absorption, the incorporation of a light-harvesting antenna is required. This Review provides an overview of the nitrogen-rich antennae in lanthanide-based temperature sensors, emitting in the visible light spectrum, and discusses their temperature sensor ability. The N-rich ligands are incorporated in many different platforms. The investigation of different antennae is required to develop temperature sensors with diverse optical properties and to create a diverse offer for the multiple application fields. Molecular probes, consisting of small molecules, are first discussed. Furthermore, the thermometer properties of ratiometric temperature sensors, based on di- and polynuclear complexes, metal-organic frameworks, periodic mesoporous organosilicas and porous organic polymers, are summarized. The antenna mainly determines the application potential of the ratiometric thermometer. It can be observed that molecular probes are operational in the broad physiological range, metal-organic frameworks are generally very useful in the cryogenic region, periodic mesoporous organosilica show temperature dependency in the physiological range, and porous organic polymers are operative in the cryogenic-to-medium temperature range.

N-Rich Porous Polymer with Isolated Tb3+ -Ions Displays Unique Temperature Dependent Behavior through the Absence of Thermal Quenching

The challenge of measuring fast moving or small scale samples is based on the absence of contact between sample and sensor. Grafting lanthanides onto hybrid materials arises as one of the most promising accurate techniques to obtain noninvasive thermometers. In this work, a novel bipyridine based porous organic polymer (bpyDAT POP) was investigated as temperature sensor after grafting with Eu(acac)₃ and Tb(acac)₃ complexes. The bpyDAT POP successfully showed temperature-dependent behavior in the 10-310 K range, proving the potential of amorphous, porous organic frameworks. We observed unique temperature dependent behavior. More intriguingly, instead of the standard observed change in emission as a result of a change in temperature for both Eu³⁺ and Tb³⁺ , the emission spectrum of Tb³⁺ remained constant. This work provides framework- and energy-based explanations for the observed phenomenon. The conjugation in the bpyDAT POP framework is interrupted, creating energetically isolated Tb³⁺ environments. Energy transfer from Tb³⁺ to Eu³⁺ is therefore absent, nor energy back transfer from Tb³⁺ to bpyDAT POP ligand (i.e. no thermal quenching) is detected.

How does the ligand affect the sensitivity of the luminescent thermometers based on Tb-Eu complexes

Theoretical description of a four-level system for luminescent thermometry was proposed. Based on this description, the sensitivity was proved not to exceed Sr =|E23 - E12|/T2, where T is the temperature and |E23 - E12| is the absolute energy difference between the excited state energy gaps. The analysis was verified for the terbium-europium coordination compounds, the most studied class of four-level thermometry systems, which revealed that most of the examples fall within either this theory or represent three-level systems, where the ligand is not involved in the thermally-activated processes. From this description, it follows that the highest Sr can be reached either when the triplet state is not involved or when the ligand triplet state is very high, which in the case of terbium-europium coordination compounds means exceeding 26 800 cm-1.

A large-area luminescent downshifting layer containing an Eu3+ complex for crystalline silicon solar cells

We present a large-area luminescent down-shifting layer consists of polyvinyl alcohol embedding a newly synthesized ternary Eu³⁺ complex. C-Si solar cell coated with this layer displayed an enhancement of ~15% in external quantum efficiency.

Photostable Anisometric Lanthanide Complexes as Promising Materials for Optical Applications

Uniform luminescent films with high optical quality are promising materials for modern molecular photonics. Such film materials based on β-diketonate complexes of lanthanides have the following application problem: rapid luminescence degradation under UV radiation, low thermostability, poor mechanical properties, and aggregation propensity. An alternative approach to solving these problems is the use of anisometric analogues of β-diketonate compounds of lanthanides (III). The main advantage of such compounds is that they do not crystallize because of long hydrocarbon substituents in the structure of complexes, so they can be used to fabricate thin nano-, micro-, and macroscale uniform film materials by a melt-processing technique at relatively low temperatures, as well as by spin-coating. The method of fabrication of microscale luminescent film materials with controlled optical properties from anisometric analogues of Ln(DBM)3Phen and Ln(bzac)3Phen complexes (Ln = Eu, Tb) is proposed in this paper. Within the framework of this research, we developed original films which are highly uniform and transparent. An important advantage of these films is their high photostability and potential for applications as reusable luminescent sensors and light converters.

The influence of dopant concentration and grain size on the ability for temperature sensing using nanocrystalline MgAl2O4:Co2+,Nd3+ luminescent thermometers

In this work, for the first time, the ability of nanocrystalline MgAl₂O₄:Co²⁺ and MgAl₂O₄:Co²⁺,Nd³⁺ phosphors for temperature sensing was investigated in a wide temperature range.

A self-calibrated luminescent thermometer based on nanodiamond-Eu/Tb hybrid materials

ND-PMA-RE was synthesized and the ND-PMA-Eu/Tb could be served as a self-referencing luminescent thermometer due to the temperature-dependent luminescence performance.

Luminescence resonance energy transfer in hybrid materials based on terbium(iii) complex, rhodamine B and nanoclay

We prepared a novel kind of luminescent hydrogel based on the combination of terbium(iii) complexes and rhodamine B dye with the LAPONITE® nanoclay.