The role of lanthanide luminescence in advancing technology

Luminescent Thermometer Based on a Praseodymium(iii) Cyanide-Based Metal-Organic Framework

Trivalent lanthanide ions have emerged as promising candidates for precise and remote temperature sensing. Among them, Pr3+-based luminescent thermometers remain underexplored, particularly those operating in the near-infrared (NIR) spectral region. This work presents the synthesis and thorough characterization of a novel Pr3+-based coordination polymer, {[Pr2IIIPt3II(CN)12(4,4'-bpyO2)4(H2O)6]·4H2O}n (1), as a rare example of Pr3+ luminescent thermometry. Coordination between Pr3+ ions, cyanido-bridged Pt2+ centers, and 4,4'-bpyO2 ligands enables efficient energy transfer, producing luminescence in visible and near-infrared regions. The polymer demonstrates distinct temperature-dependent luminescence over a wide range (12-386 K), with relative thermal sensitivities of ≅1%·K-1 and a minimum temperature uncertainty of 0.2 K.

Energy exchange between Nd3+ and Er3+ centers within molecular complexes

Developing controlled and reproducible molecular assemblies incorporating lanthanide centers is a crucial step for driving forward up- and down-conversion processes. This challenge calls for the development of strategies to facilitate the efficient in situ segregation of different Ln metal ions into distinct positions within the molecule. The unique family of pure [LnLn'Ln] heterometallic coordination compounds previously developed by us represents an ideal platform for studying the desired Ln-to-Ln' energy transfer (ET). In this context, we report here the new pure one-step synthetically produced [ErNdEr] (3) complex, which allows for the first time at the molecular level to study the mechanisms behind Nd-to-Er energy transfer. To further assess the photophysical properties of this complex, the analogous [LuNdLu] (1) and [ErLaEr] (2) complexes have also been prepared and photophysically studied. Efficient sensitization via the two β-diketones employed as main ligands was probed for both Nd3+ and Er3+ ions, resulting in highly resolved emission spectra and sufficiently long excited state lifetimes, which allowed further assessment of the Ln-to-Ln' ET. This intermetallic transfer was first detected by comparing the emission spectra of iso-absorbant solutions and demonstrated by comparing the lifetime values with or without the lanthanide quencher (Er3+), as well as with a deep analysis of the excitation spectrum of the three complexes. Thus, a very unique phenomenon was discovered, consisting of a mutual Nd-to-Er and Er-to-Nd ET with no net increase of brightness by any metal; while Nd3+ transfers the energy received from the antenna to Er3+, the sensitization of the latter results in back-transfer to Nd3+ into a non-emissive, thus silent, state.

Photon shifting and trapping in perovskite solar cells for improved efficiency and stability

Advanced light management techniques can enhance the sunlight absorption of perovskite solar cells (PSCs). When located at the front, they may act as a UV barrier, which is paramount for protecting the perovskite layer against UV-enabled degradation. Although it was recently shown that photonic structures such as Escher-like patterns could approach the theoretical Lambertian-limit of light trapping, it remains challenging to also implement UV protection properties for these diffractive structures while maintaining broadband absorption gains. Here, we propose a checkerboard (CB) tile pattern with designated UV photon conversion capability. Through a combined optical and electrical modeling approach, this photonic structure can increase photocurrent and power conversion efficiency in ultrathin PSCs by 25.9% and 28.2%, respectively. We further introduce a luminescent down-shifting encapsulant that converts the UV irradiation into Visible photons matching the solar cell absorption spectrum. To this end, experimentally obtained absorption and emission profiles of state-of-the-art down-shifting materials (i.e., lanthanide-based organic-inorganic hybrids) are used to predict potential gains from harnessing the UV energy. We demonstrate that at least 94% of the impinging UV radiation can be effectively converted into the Visible spectral range. Photonic protection from high-energy photons contributes to the market deployment of perovskite solar cell technology, and may become crucial for Space applications under AM0 illumination. By combining light trapping with luminescent downshifting layers, this work unravels a potential photonic solution to overcome UV degradation in PSCs while circumventing optical losses in ultrathin cells, thus improving both performance and stability.

Elucidating the Mechanism of Efficient Eu(III) and Yb(III) Sensitisation from a Re(I) Tetrazolato Triangular Assembly

The reaction of Re(CO)5Br with deprotonated 1H-(5-(2,2':6',2''-terpyridine)pyrid-2-yl)tetrazole yields a triangular assembly formed by tricarbonyl Re(I) vertices. Photophysical measurements reveal blue-green emission with a maximum at 520 nm, 32 % quantum yield, and 2430 ns long-lived excited state decay lifetime in deaerated dichloromethane solution. Coordination of lanthanoid ions to the terpyridine units red-shifts the emission to 570 nm and also reveals efficient (90 %) and fast sensitisation of both Eu(III) and Yb(III) at room temperature, with a similar rate constant kET on the order of 107 s-1. Efficient sensitisation of Eu(III) from Re(I) is unprecedented, especially when considering the close proximity in energy between the donor and acceptor excited states. On the other hand, comparative measurements at 77 K reveal that energy transfer to Yb(III) is two orders of magnitude slower than that to Eu(III). A two-step mechanism of sensitisation is therefore proposed, whereby the rate-determining step is a thermally activated energy transfer step between the Re(I) centre and the terpyridine functionality, followed by rapid energy transfer to the respective Ln(III) excited states. At 77 K, the direct Re(I) to Eu(III) energy transfer seems to proceed via a ligand-mediated superexchange Dexter-type mechanism.

Spectroscopic Studies of Lanthanide(III) Complexes with L-Malic Acid in Binary Systems

Binary systems of lanthanide ions (La, Nd, Gd, Ho, Tb, and Lu) with L-malic acid in molar ratios of 1:1 and 1:2 were studied. This study was carried out in aqueous solutions, and the composition of the formed complexes was confirmed using computer data analysis. The overall stability constants of the complexes and the equilibrium constants of the reaction were determined. The effect of ligand concentration on the composition of the internal coordination sphere of the central atom was observed. Changes in the coordination sphere of lanthanide ions were confirmed by spectroscopic measurements.

Development of Broad-Range Microbial Minimal Culture Medium for Lanthanide Studies

Rare Earth Elements (REE), also known as Lanthanides (Ln3+), are a group of 17 elements showing peculiar physical and chemical properties. Unlike technological applications, very little is known about the physiological role and toxicity of Ln3+ on biological systems, in particular on microorganisms (e.g., bacteria), which represent the most abundant domains on our planet. Up to now, very limited studies have been conducted due to Ln3+ precipitation with some anions commonly present in the culture media. Therefore, the development of a minimal medium is essential to allow the study of Ln3+-microbial interactions, limiting considerably the precipitation of insoluble salts. In this regard, a new minimal culture medium capable of solubilizing large amounts of Ln3+ and allowing the growth of different microbial taxa was successfully developed. Assays have shown that the medium is capable of solubilizing Ln3+ up to 100 times more than other common culture media and allowing the growth of 63 bacteria and 5 fungi. The kinetic growth of one yeast and one Gram-positive bacterium has been defined, proving to support superior growth and biomass compared to other commonly used minimal media. Moreover, the sensitivity and uptake/absorption of a Bacillus stratosphericus strain were tested, highlighting its capability to tolerate concentrations up to 10 mM of either Cerium, Gadolinium or Lanthanum and accumulate different quantities of the three.

Luminescent Supramolecular Metallogels: Drug Loading and Eu(III) as Structural Probe

Supramolecular metallogels combine the rheological properties of gels with the color, magnetism, and other properties of metal ions. Lanthanide ions such as Eu(III) can be valuable components of metallogels due to their fascinating luminescence. In this work, we combine Eu(III) and iminodiacetic acid (IDA) into luminescent hydrogels. We investigate the tailoring of the rheological properties of these gels by changes in their metal:ligand ratio. Further, we use the highly sensitive Eu(III) luminescence to obtain information about the chemical structure of the materials. In special, we take advantage of computational calculations to employ an indirect method for structural elucidation, in which the simulated luminescent properties of candidate structures are matched to the experimental data. With this strategy, we can propose molecular structures for different EuIDA gels. We also explore the usage of these gels for the loading of bioactive molecules such as OXA, observing that its aldose reductase activity remains present in the gel. We envision that the findings from this work could inspire the development of luminescent hydrogels with tunable rheology for applications such as 3D printing and imaging-guided drug delivery platforms. Finally, Eu(III) emission-based structural elucidation could be a powerful tool in the characterization of advanced materials.

Interlaboratory Comparison on Absolute Photoluminescence Quantum Yield Measurements of Solid Light Converting Phosphors with Three Commercial Integrating Sphere Setups

Scattering luminescent materials dispersed in liquid and solid matrices and luminescent powders are increasingly relevant for fundamental research and industry. Examples are luminescent nano- and microparticles and phosphors of different compositions in various matrices or incorporated into ceramics with applications in energy conversion, solid-state lighting, medical diagnostics, and security barcoding. The key parameter to characterize the performance of these materials is the photoluminescence/fluorescence quantum yield (Φf), i.e., the number of emitted photons per number of absorbed photons. To identify and quantify the sources of uncertainty of absolute measurements of Φf of scattering samples, the first interlaboratory comparison (ILC) of three laboratories from academia and industry was performed by following identical measurement protocols. Thereby, two types of commercial stand-alone integrating sphere setups with different illumination and detection geometries were utilized for measuring the Φf of transparent and scattering dye solutions and solid phosphors, namely, YAG:Ce optoceramics of varying surface roughness, used as converter materials for blue light emitting diodes. Special emphasis was dedicated to the influence of the measurement geometry, the optical properties of the blank utilized to determine the number of photons of the incident excitation light absorbed by the sample, and the sample-specific surface roughness. While the Φf values of the liquid samples matched between instruments, Φf measurements of the optoceramics with different blanks revealed substantial differences. The ILC results underline the importance of the measurement geometry, sample position, and blank for reliable Φf data of scattering the YAG:Ce optoceramics, with the blank's optical properties accounting for uncertainties exceeding 20%.

Silica-coated LiYF4:Yb3+, Tm3+ upconverting nanoparticles are non-toxic and activate minor stress responses in mammalian cells

Lanthanide-doped upconverting nanoparticles (UCNPs) are ideal candidates for use in biomedicine. The interaction of nanomaterials with biological systems determines whether they are suitable for use in living cells. In-depth knowledge of the nano-bio interactions is therefore a pre-requisite for the development of biomedical applications. The current study evaluates fundamental aspects of the NP-cell interface for square bipyramidal UCNPs containing a LiYF4:Yb3+, Tm3+ core and two different silica surface coatings. Given their importance for mammalian physiology, fibroblast and renal proximal tubule epithelial cells were selected as cellular model systems. We have assessed the toxicity of the UCNPs and measured their impact on the homeostasis of living non-malignant cells. Rigorous analyses were conducted to identify possible toxic and sub-lethal effects of the UCNPs. To this end, we examined biomarkers that reveal if UCNPs induce cell killing or stress. Quantitative measurements demonstrate that short-term exposure to the UCNPs had no profound effects on cell viability, cell size or morphology. Indicators of oxidative, endoplasmic reticulum, or nucleolar stress, and the production of molecular chaperones varied with the surface modification of the UCNPs and the cell type analyzed. These differences emphasize the importance of evaluating cells of diverse origin that are relevant to the intended use of the nanomaterials. Taken together, we established that short-term, our square bipyramidal UCNPs are not toxic to non-malignant fibroblast and proximal renal epithelial cells. Compared with established inducers of cellular stress, these UCNPs have minor effects on cellular homeostasis. Our results build the foundation to explore square bipyramidal UCNPs for future in vivo applications.

Rare Earths-The Answer to Everything

Rare earths, scandium, yttrium, and the fifteen lanthanoids from lanthanum to lutetium, are classified as critical metals because of their ubiquity in daily life. They are present in magnets in cars, especially electric cars; green electricity generating systems and computers; in steel manufacturing; in glass and light emission materials especially for safety lighting and lasers; in exhaust emission catalysts and supports; catalysts in artificial rubber production; in agriculture and animal husbandry; in health and especially cancer diagnosis and treatment; and in a variety of materials and electronic products essential to modern living. They have the potential to replace toxic chromates for corrosion inhibition, in magnetic refrigeration, a variety of new materials, and their role in agriculture may expand. This review examines their role in sustainability, the environment, recycling, corrosion inhibition, crop production, animal feedstocks, catalysis, health, and materials, as well as considering future uses.

Tridentate Nitrogen Ligand as a Tool for the Construction of Well-Defined Rare Earth Trichloride Complexes

LnCl3(THF)3 (Ln = Y, La ÷ Nd, Sm ÷ Lu) readily react with the tridentate 1,3,5-trimethyl-1,3,5-triazacyclohexane (Me3tach) ligand to form mono- or binuclear lanthanide trichloride complexes, depending on the stoichiometry of the reaction and the ionic radius of the metal: mononuclear pseudosandwich [LnCl3(Me3tach)2], (Ln = Y, La ÷ Ho) or binuclear complexes [Ln2Cl6(Me3tach)3], or [LnCl3(Me3tach)(THF)]2 (Ln = Sm, Tb). Detailed analysis of the NMR data of [LnCl3(Me3tach)2] complexes with paramagnetic lanthanide ions showed that their structures remained unchanged in the toluene solution. A series of isomorphous complexes [LnCl3(Me3tach)(Py)2] (Ln = La, Sm, Tb, Er, Lu; Py = pyridine) have been obtained by the recrystallization of either mononuclear or binuclear complexes from pyridine. Complexes of terbium and europium ions with the Me3tach ligand exhibit relatively high quantum yields of metal-centered luminescence (0.39 and 0.32, respectively).

Tailoring the pore size of expanded porphyrinoids for lanthanide selectivity

Despite increase in demand, capacity for the recycling of rare earth elements remains limited, partly due to the inefficiencies with processes currently utilised in the separation of lanthanides. This study highlights the potential use of expanded porphyrinoids in lanthanide separation through selective binding, dependent on the tailored pore size of the macrocycle. Each emerging trend is subjected to multi-factored analysis to decompose the underlying source. Results promote the viability of size-based separation with preferential binding of larger lanthanum(iii) ions to amethyrin and isoamethyrin macrocycles, while smaller macrocycles such as pentaphyrin(0.0.0.0.0) present a preferential binding of lutetium(iii) ions. Additionally, the porphyrin(2.2.2.2) macrocycle shows a selectivity for gadolinium(iii) ions over both larger and smaller ions. An upper limit of applicable pore size is shown to be ≈2.8 Å, beyond which the formed complexes are predicted to be less stable than the corresponding nitrate complexes.