Trivalent Lanthanide Ions Research Articles

Apparent Interfacial Toughness of Undoped and Photoluminescent Eu3+-Doped Yttria-Stabilized Zirconia Thermal Barrier Coatings

Most photoluminescence methods for the diagnostic of thermal barrier coatings (TBC) rely on the functionalization of yttria-stabilized zirconia (YSZ) with trivalent lanthanide ions. It consists in determining temperature and detecting preventively damages within the volume of the TBC prior to ceramic topcoat spallation. The latter depends on the interfacial toughness, which is an important factor to address thermal barrier coating’s performance and durability. In this paper, the influence of the addition of rare earth elements (Eu3+) on the interfacial toughness of TBC deposited by atmospheric plasma spray is investigated. Two types of coatings are deposited and investigated: (1) Type I: coating deposited using Eu3+-doped YSZ powder (2 mol.%), (2) Type II: coating deposited using undoped YSZ powder. Both types of coatings are heat-treated at 1100 °C under isothermal conditions using different oxidation exposure times: 100, 300 and 800 h. The morphology of the interface between the topcoat (TBC) and the bond coat is analyzed by scanning electron microscopy. The apparent interfacial toughness is investigated using indentation. It is shown that the interfacial apparent toughness decreases as the oxidation exposure time increases. Concomitantly, the thickness of the thermally grown oxide (TGO) layer between the bond coat and the topcoat increases. Results show as well that the partial substitution of Y3+ ions by a low amount of Eu3+ ions (2 mol.%) does not have influence on the microstructure and the interfacial toughness of the YSZ coatings. In addition, energy dispersive spectrometry reveals that there is no diffusion of Eu3+ into the TGO layer. It is therefore concluded that the use of Eu3+ for damage diagnostic based on photoluminescence methods will not induce any kind of degradation of the properties of TBCs.

Intense single-band red upconversion emission in BiOCl:Er3+ layered semiconductor via co-doping Ho3+

Exploring a new tuning way to facilely realize single-band red emission in trivalent rare-earth ions (RE3+) doped upconversion (UC) materials is still desirable. In this work, the intense single-band red emission is achieved by co-doping only Ho3+ in the BiOCl: Er3+ under 1550 nm excitation. In the BiOCl layered host, co-doping Ho3+ can further enhance the red emission and simultaneously suppress the green emission of Er3+, and thus obviously improve the red-to-green (R/G) ratio. It is found that Ho3+ does not serve as energy trapping through the 5I6 state as in traditional UC materials but acts as ET bridge (4S3/2, 2H11/2 (Er3+) → 5F4, 5S2 (Ho3+) → 4F9/2 (Er3+)). The tuning mechanism of Ho3+ is discussed in detail and further confirms through a comparative experiment. Our research gives an unusual perspective to tune the UC behavior of Er3+ through co-doping Ho3+, which might be inspiring for achievement of single-band red UC emission.

Optical analysis and separation of trivalent lanthanides in deep eutectic solvents

Deep eutectic solvents (DESs) were used for luminescence measurements in quantitative analysis of trivalent lanthanide ions and as solvents for light rare earth elements (LREE) in solid-liquid separation. The spectroscopic characteristics of lanthanide chlorides LnCl3 (Ln = Eu, Tb), respectively their aquo complexes, are described in a comprehensive study that demonstrates the significant enhancement of the phosphorescence emission intensity in DESs as polar and weakly coordinating solvent. Several DESs stabilize the lanthanide ion luminescence against changes in temperature and moisture, which is advantageous compared with the use of ionic liquids. Small amounts of water lead in certain eutectic systems even to a further increase in phosphorescence emission intensity. By investigating the solubility of lanthanide sesquioxides Ln2O3 (Ln = La, Nd, Sm, Eu, Gd, Tb, Dy) in DESs, selectivities are identified that may be of use for the separation of LREE.

Titanium effect on the structural, morphological and transport properties of La0.7Sr0.3Mn1-xTixO3 (x = 0.03, 0.06 and 0.12)

A formidable amount of work has been devoted aiming towards the understanding of the structure and properties of colossal magnetoresistance (CMR) manganites. Mixed valent manganites with the general formula R1-xAxMnO3 (R = trivalent rare earth ion and A = divalent ion like Sr+2, Ba+2, Pb+2, Ca+2 etc.) are found to exhibit variety of phenomena such as charge, spin and orbit ordering, electronic, magnetic and structural transitions depending on the type and amount of doping (x). In this paper, doping dependent modifications in the microstructure polycrystalline La0.7Sr0.3Mn1-xTixO3 (LSMTO) (x = 0.03, 0.06 and 0.12) compounds synthesized by hybrid method (sol gel method + solid state reaction method) have been discussed in detail. In the present work, the powder X-ray diffraction patterns reveals that the samples are single phase in nature and the samples show a rhombohedral structure in hexagonal lattice with the space group R3-c. The Rietveld refinement was performed using FullProf software for the detailed structural investigation. In this context, the lattice parameters, unit cell volume and χ2 were obtained for LSMTO samples. On the substitution of Mn+4 by Ti+4, the structure does not undergo any phase transformation, but lattice parameters steadily increase as Ti+4 doping concentration increases. It can be related to the larger ionic radius of Ti+4 (rTi+4 = 0.605 Å) ion compared to that of Mn+4 (rMn+4 = 0.540 Å) ion. FT-IR spectra for LSMTO of different concentration show the four peaks around 400–500 cm−1 (Mn-O-Mn bending mode), 610–670 cm−1 (Mn-O stretching mode), 2330–2400 cm−1 (moisture contain) and 540 cm−1 (Ti-O stretching modes). Weight loss % versus temperature plot (TGA) for the x = 0.06 sample confirms that the precursor shows three step weight loss profiles and does not melt up to the temperature of 1050 °C. A quantitative analysis of the energy dispersive spectroscopy (EDS) data indicates that the observed concentration of elements is very close to the calculated values from its chemical formula. Typical SEM micrographs for all the three samples show that each sample possesses fine and clear grain boundaries (GBs). From the R-T measurements, an increase in resistivity and a decrease in metal to insulator transition temperature (TMI) were observed by increasing doping level of Ti for Mn. All the LSMTO samples show the resistivity suppression under applied magnetic field. The maximum MR % (89%) was observed for x = 0.12 at 5 T compare to other doped samples. This result suggests that the magnetoresistance behavior is improved by addition of Ti at Mn. These results prove that concentration Ti substitution at Mn site enhances the various properties of this manganite system.

Squares of gold atoms and linear infinite chains of Cd atoms as building units in the intermetallic phases REAu4Cd2 (RE=La–Nd, Sm) with YbAl4Mo2-type structure

Abstract The gold-rich intermetallic compounds REAu4Cd2 (RE = La–Nd, Sm) were synthesized from the elements in sealed tantalum ampoules. Their characterization by X-ray powder and single crystal data confirmed the tetragonal YbAl4Mo2 type, space group I4/mmm. The basic building units are Au4 squares (278 pm Au–Au in CeAu4Cd2) and infinite linear cadmium chains (275 pm Cd–Cd in CeAu4Cd2). We exemplarily studied the solid solution CeAu4+ x Cd2− x for x = 0–1 up to CeAu5Cd. Electron diffraction patterns on a CeAu5Cd sample confirm the single crystal data. They give no hint for complete gold-cadmium ordering. Temperature-dependent magnetic susceptibility measurements of CeAu4Cd2, CeAu5Cd, PrAu4Cd2 and NdAu4Cd2 show stable trivalent rare earth ions and give no hint for magnetic ordering above 3 K.

Synthesis and characterization of luminescent Ln3+ (Ln = Eu, Tb and Dy)-doped LiYF4 microcrystals produced by a facile microwave-assisted hydrothermal method

This paper reports microstructural and luminescent properties of lithium yttrium fluoride (LiYF4) doped with rare earth ions. Submicrometric crystals of LiYF4 were successfully produced using the microwave-assisted hydrothermal method, which allowed the formation of single crystalline phase at temperatures as low as 140 °C for a reaction time of 15 min. The structural study was carried out by X-ray diffraction (XRD), revealing single tetragonal phase. The electronic structure and microstructure formation of LiYF4 was investigated through the binding energy of the atoms, measured via X-ray photoemission spectroscopy (XPS) and scanning electron microscopy (SEM). The luminescent properties as scintillator were investigated through X-ray excited luminescence (XEL) and time-resolved luminescence. Spectroscopy studies were done via photoluminescence (PL) technique in the visible (VIS) and vacuum ultraviolet (VUV) regions, from ∼1.0 to 15.0 eV. PL excitation results showed that the band gap (Eg) of the LiYF4 is at around 11.0 (±0.1) eV. 4f-5d transitions were identified for Eu3+, Tb3+ and Dy3+. The experimental data were used to predict the energy levels of all divalent and trivalent lanthanide (Ln) ions relative to the valence and conduction bands of LiYF4 and to construct the host referred binding energy (HRBE) and vacuum referred binding energy (VRBE) schemes.

Tailoring the local lattice distortion of Nd3+ by codoping of Y3+ through first principles calculation for tuning the spectroscopic properties

Trivalent rare earth ions have rich and unique energy levels arising from 4f inner shell configurations, which can be widely used in lasers, display, and bioimaging, etc. As the f-f transition of the rare earth ions is parity-forbidden, it is necessary to dope the active ions in the host with an appropriate coordination structure to relax the forbidden. In this work, a first principles calculation based on the density functional theory was applied to investigate the local structure symmetries of Nd3+ ions in Nd3+,Y3+:SrF2 crystal. The computational results show that the clusters of [mNd3+-nY3+] (m + n = 2, 3, 4, 5 and 6) would be formed when Y3+ is codoped in Nd3+:SrF2 crystal. The formation energy of the [mNd3+-nY3+] cluster decreases when the value of m + n increases, or the value of n increases with m + n fixed, then the lattice structure becomes more stable. Furthermore, the first coordination shell of Nd3+ was cubic when the n ≤ 1, and it would transform to be the lower symmetric square antiprism structure with n ≥ 2. The forbidden of the electric dipole transition was thus relaxed due to breaking of the symmetry. The experimental results show the absorption cross section of Nd3+ was increased from 0.45 ×10−20 cm2 to 5.2×10−20 cm2, and the emission intensity was also enhanced by about 20 times through codoping Y3+ ions, which agreed well with the calculated results. It suggests that the tailoring of the local lattice distortion of the active ions may open interesting possibilities in the design of rare earth doped materials.

Structural and photoluminescence properties of Y2O3 and Y2O3:Ln3+ (Ln = Eu, Er, Ho) films synthesized by plasma electrolytic oxidation of yttrium substrate

Plasma electrolytic oxidation (PEO) of yttrium is performed for the first time and is shown that Y2O3 and trivalent rare-earth ions (Eu3+, Er3+ or Ho3+) doped Y2O3 films can be formed by PEO in alkaline electrolyte without or with addition of rare-earth oxide particles (Eu2O3, Er2O3 or Ho2O3), respectively. The elements present in PEO micro-discharges were identified using optical emission spectroscopy technique. The gas plasma temperature of (3000 ± 300) K was estimated from the intensity distribution within a part of an OH spectrum. The morphology, chemical composition, crystal structure, formation process and photoluminescence (PL) properties of formed films were investigated. Diffraction patterns of formed films show well pronounced reflections inherent to pure cubic phase of Y2O3. PL characterization of Y2O3 and Y2O3:Ln3+ (Ln = Eu, Er, Ho) films is performed through excitation and emission spectra. An intense red PL emission was observed from the Y2O3:Eu3+ and a green emission was observed from Y2O3:Er3+ and Y2O3:Ho3+ films.

Thermoluminescence Enhancement of LiMgPO4 Crystal Host by Tb3+ and Tm3+ Trivalent Rare-Earth Ions Co-doping.

We investigated the influence of terbium and thulium trivalent rare-earth (RE) ions co-doping on the luminescent properties enhancement of LiMgPO4 (LMP) crystal host. The studied crystals were grown from the melt by micro-pulling-down (MPD) technique. Luminescent properties of the obtained crystals were investigated by thermoluminescence (TL) method. The most favorable properties and the highest luminescence enhancement were measured for Tb and Tm double doped crystals. A similar luminescence level can be also obtained for Tm, B co-doped samples. In this case, however, the low-temperature TL components have a significant contribution. The measured luminescent spectra showed a typical emission of Tb3+ and Tm3+ ions of an opposite trapping nature, namely the holes and electron-trapping sites, respectively. The most prominent transitions of 5D4 → 7F3 (550 nm for Tb3+) and 1D2 → 3F4 (450 nm for Tm3+) were observed. It was also found that Tb3+ and Tm3+ emissions show temperature dependence in the case of double doped LMP crystal sample, which was not visible in the case of the samples doped with a single RE dopant. At a low temperature range (up to around 290 °C) Tm3+ emission was dominant. At higher temperatures, the electrons occupying Tm3+ sites started to be released giving rise to emissions from Tb-related recombination centers, and emissions from Tm3+ centers simultaneously decreased. At the highest temperatures, emission took place from Tb3+ recombination centers, but only from deeper 5D4 level-related traps which had not been emptied at a lower temperature range.

Tailoring Multidimensional Traps for Rewritable Multilevel Optical Data Storage.

In the current "big data" era, the state-of-the-art optical data storage (ODS) has become a front-runner in the competing data storage technologies. As one of the most promising methods for breaking the physical limitation suffered by traditional ones, the advance of optically stimulated luminescence (OSL) based optical storage technique is now still limited by the simultaneous single-level write-in and readout in a same spot. In this work, to bridge the data-capacity gap, we report for the first time a novel and promising nonphysical multidimensional OSL-based ODS flexible medium for erasable multilevel optical data recording and reading. We tailor multidimensional traps with discrete, narrowly distributed energy levels through (multi-)codoping of selective trivalent rare-earth ions into Eu2+-activated barium orthosilicate (Ba2SiO4). Upon UV/blue light illumination, information can be sequentially recorded in different traps assisted by thermal cleaning with an increase of storage capacity by orders of magnitude, which is addressable individually in the whole domain or bit-by-bit mode without the crosstalk by designed thermal/optical stimuli. Remarkably, good data retention and robust fatigue resistance have been achieved in recycle data recording. Insight is forged from charge carrier dynamics and interactions with traps for a universal method of data storage, and proof-of-concept applications are also demonstrated, thereby providing the way to not only rewritable multilevel ODS but also high-security encryption/decryption.

Luminescent calcium carbonate micro ‘bow ties’

Calcium carbonate (CaCO3) is a ubiquitous material which has been studied for centuries due to its integral nature across various fields and its vast range of applications. Here we report, for the first time, a low temperature dry ice carbonation method for the production of unique rare earth-doped calcium carbonate ‘bow ties’. CaCO3 exhibits retrograde solubility, an interesting property in which its solubility increases with decreasing temperature. In this synthesis, dry ice acts not only as a CO2 source, but as a coolant, increasing the solubility of CaCO3 and CO2 and allowing specific growth to occur. The incorporation of trivalent lanthanide ions Eu3+ and Tb3+ into the CaCO3 synthesis results in the formation of these unique luminescent calcite ‘bow tie’ microstructures which cannot be produced using either standard gaseous CO2 carbonation, or chemical precipitation methods. This new method and materials might find potential applications including, but not limited to, radionuclide sequestration, imaging and photonics.

Potential Application of Upconverting Nanoparticles for Brain Photobiomodulation.

Brain photobiomodulation (PBM) describes the use of visible to near-infrared light for modulation or stimulation of the central nervous system in both healthy individuals and diseased conditions. Although the transcranial approach to delivering light to the head is the most common technique to stimulate the brain, delivery of light to deeper structures in the brain is still a challenge. The science of nanoparticle engineering in combination with biophotonic excitation could provide a way to overcome this problem. Upconversion is an anti-Stokes process that is capable of transforming low energy photons that penetrate tissue well to higher energy photons with a greater biological effect, but poor tissue penetration. Wavelengths in the third optical window are optimal for light penetration into brain tissue, followed by windows II, IV, and I. The combination of trivalent lanthanide ions within a crystalline host provides a nanostructure that exhibits the upconversion phenomenon. Upconverting nanoparticles (UCNPs) have been successfully used in various medical fields. Their ability to cross the brain-blood barrier and their low toxicity make them a good candidate for application in brain disorders. It is possible that delivery of UCNPs to the brainstem or deeper parts of the cerebral tissue, followed by irradiation using light wavelengths with good tissue penetration properties, could allow more efficient PBM of the brain.

Characterization of Ce-doped RE3Al5O12 (RE=Tb, Dy, Ho, Er, Tm and Yb) single crystalline scintillators

Ce-doped RE3Al5O12 (Ce:REAG, RE=Tb, Dy, Ho, Er, Tm and Yb) single crystals were synthesized by the optical Floating Zone method. The transmittance is approximately 80% in all the samples, and absorptions by rare-earth ions were observed. Under X-ray irradiation, Ce:TbAG, Ce:DyAG, Ce:HoAG and Ce:TmAG exhibit scintillation signals with a broad emission band around 500–700 nm, which is attributable to the 5d–4f transitions of Ce3+. Several emission peaks due to F+ centers and 4f–4f transitions of trivalent rare-earth ions are also observed in some samples. In afterglow properties, Ce:Tb3Al5O12 and Ce:Yb3Al5O12 showed better afterglow levels than the other samples.

Molecular neurochemistry of the lanthanides.

Lanthanides, once termed rare-earth elements, are not as sparce in the environment as their traditional name suggests. Mean litospheric concentrations are in fact comparable to the physiologically fundamental elements such as iodine, cobalt, and selenium. Recent advances in medical technology have resulted in accumulation of lanthanides presenting potential exposure to both our central and peripheral nervous systems. Extensive and detailed studies on these peculiar active metals in the context of their influence on neural functions are therefore urgently required. Almost all neurochemical effects of trivalent lanthanide ions appear to result from the similarity of their radii to the key signaling ion calcium. Lanthanides, especially La3+ and Gd3+ block different types of calcium, potassium, and sodium channels in human and animal neurons, regulate neurotransmitter turnover and release, as well as synaptic activity. Lanthanides also act as modulators of several ionotropic receptors, e.g., GABA, NMDA, and kainate and can also affect numerous signaling mechanisms including NF-κB and apoptotic-related endoplasmic reticulum IRE1-XBP1, PERK, and ATF6 pathways. Several lanthanide ions may cause oxidative neuronal injuries and functional impairment by promoting reactive oxygen species production. However, cerium and yttrium oxides have some unique and promising neuroprotective properties, being able to decrease free radical cell injury and even alleviate motor impairment and cognitive function in animal models of multiple sclerosis and mild traumatic brain damage, respectively. In conclusion, lanthanides affect various neurophysiological processes, altering a large spectrum of brain functions. Thus, a deeper understanding of their potential mechanistic roles during disease and as therapeutic agents requires urgent elucidation.

The nephelauxetic effect on the electron binding energy in the 4fq ground state of lanthanides in compounds

In the construction of a vacuum referred binding energy (VRBE) diagram with the lanthanide 4fq ground states, always a compound independent variation with the number q= 1 to 14 is assumed. Experimental data from thermo-luminescence, intervalence charge transfer bands, and thermo-bleaching studies provide first indications that a minor compound dependence does exist. To explain its origin we will first apply Jørgensen spin pairing theory to reproduce the VRBE in the ground states of the free di- and trivalent lanthanide ions which is equivalent to the 3rd and 4th ionization potentials of the lanthanide atoms. By combining experimental data and calculated trends therein, the relevant Racah E1, Racah E3, and spin orbit coupling ζff parameters for all di-, tri-, and tetravalent free ion lanthanides are derived. Using that as input for the spin pairing theory, the characteristic zigzag shapes in VRBE as function of q, as derived from ionization potentials, are nicely reproduced. Because of the nephelauxetic effect the parameter values are lowered when lanthanides are in compounds. How that reduction affects the VRBE curves will be treated in this work.

Systematic first-principles calculations of charge transfer transitions of trivalent rare earth ions in CaF2

In order to predict the LMCT energies for various trivalent rare earth (RE) ions in CaF2 nonempirically, we performed first-principles calculations using REF85− cluster using the relativistic Discrete Variational Multi-Electron (DVME) method, which is based on the configuration interaction (CI) approach, and constructed the theoretical energy diagram of the RE 4f levels within the band gap. The theoretical Ligand to Metal Charge Transfer (LMCT) energies were overestimated in the case of simple CI calculations. Therefore in order to overcome this problem we considered the configuration-dependent correction (CDC) and the effect of lattice relaxation based on the Shannon's crystal radii. As a result, the quantitative agreement between the theoretical LMCT energies and the experimental ones was greatly improved and the characteristic dependence of the LMCT energies on atomic species was also successfully reproduced without any experimental parameter.

Random laser in Nd:YBO3 nanocrystalline powders presenting luminescence concentration quenching

Enhancement of the random laser (RL) performance in crystalline nanopowders of vaterite-type orthoborate NdxY1.000-xBO3 (0.015 ≤ x ≤ 0.040) was investigated by exciting the trivalent neodymium ions (Nd3+) at 806 nm in resonance with the ground state transitions 4I9/2→ {4F5/2, 2H9/2}. RL emission at 1056 nm, due to the Nd3+ transition 4F3/2 → 4I11/2, was observed and characterized. Although luminescence concentration quenching was detected for x > 0.007, an improvement of the RL performance was demonstrated for large Nd3+ concentrations. This feature was understood considering that the RL onset time is shorter than the nonradiative relaxation time of the 4F3/2 emitting state. The experimental results are supported by numerical simulations based on coupled rate-equations for the excited ions density and the number of photons participating in the random lasing process. The present results can motivate further RL studies with large concentration of trivalent rare-earth ions in glassy, ceramics, and crystalline matrices, which are normally avoided due to the concentration quenching.

VUV spectroscopic properties and 4fn-15d level positions of trivalent lanthanide ions doped into Na3Y(BO3)2

Luminescence spectroscopic properties of lanthanide ions (Ce3+, Pr3+, Gd3+, Tb3+, and Dy3+) doped into Na3Y(BO3)2 were investigated upon UV-VUV excitation with synchrotron radiation. The positions of 4fn–15d state of Ce3+, Pr3+, Tb3+ and Dy3+ in host matrix Na3Y(BO3)2 were deduced according to the excitation spectra. Crystal-field depression D(A), an important parameter to predict the positions of the lowest 4fn–15d levels, was established on the basis of the 5d levels of Ce3+ in Na3Y(BO3)2. Then, the average value of D(A) was obtained and further verified for 4fn–15d configurations of Pr3+, Tb3+ and Dy3+ in Na3Y(BO3)2. Finally, the lowest 4fn–15d levels of the other trivalent lanthanide ions in Na3Y(BO3)2 were predicted. The spectroscopic information on 4fn–15d levels of lanthanide ions in Na3Y(BO3)2 may provide new insights useful for designing of new efficient scintillators and WLED phosphors.

Ternary Complex Formation and Extraction Modeling in Malonate-Buffered Trivalent Actinide-Lanthanide Separations.

The formation of an aqueous ternary complex was investigated in the malonate-based Advanced TALSPEAK system by solvent extraction and optical spectroscopy. Features of the spectroscopy confirmed the presence of a ternary complex between malonate, HEDTA, and the trivalent americium or lanthanide ion. The ternary complex was then incorporated into a solvent extraction model to refine stability constants under Advanced TALSPEAK conditions. Good agreement was found in the equilibrium constants determined by both methods. These values were then used to model metal speciation and predict extraction behavior at different concentrations of malonate and HEDTA. Calculated metal distribution ratios show good correlation with experimental values. The apparent simplicity of the chemical interactions and predictability of malonate-buffered Advanced TALSPEAK provides a significant advantage over the less ideal interactions of conventional TALSPEAK.

On the structures of dinuclear symmetric lanthanide complexes and the selectivity towards heterodinuclear complexes based on molecular modeling

Homo- and heterodinuclear lanthanide complexes are important platforms for studying lanthanide-lanthanide (Ln-Ln) interactions and how they affect their luminescent and magnetic properties. Thus, methods that can yield the selective formation of these complexes are relevant. In fact, dinuclear complexes of trivalent lanthanide ions with identical coordination sites [(H2O)3L2Ln(L)2Ln′L2(H2O)3] ≡ [LnLn′]s, with L = F5C6COO−, have been synthesized, including heteronuclear [EuTb]s complex. The origin of this selectivity, for complexes with Ln, Ln′ = Eu3+, Gd3+, and Tb3+, was then investigated by quantum chemical modeling. Of the semiempirical (Sparkle/SE) and density functional theory (DFT) based approaches, only the B3LYP functional reproduced the asymmetric coordination modes of the bridging ligands and also provided the smallest deviation from the crystallographic structure. Trends in the coordination distances consistent with the Eu3+ trivalent lanthanide ionic radii were observed. However, the Ln-Ln′ distances did not follow the trends of the ionic radii and had an important impact into the electronic energies of the complexes. The selectivity towards the heterodinuclear complexes was quantified by the Gibbs energy of the [LnLn]s + [Ln′Ln′]s ⇄ 2[LnLn′]s reaction. A combined DFT approach (B3LYP for structure and M06-2X for electronic energy) was successful in showing the formation of the [EuTb]s complex. However, it was predicted that the heterodinuclear complexes [EuGd]s and [GdTb]s should not be formed. The driving force for the selectivity towards the [EuTb]s complex was the reaction (electronic) energy, whereas the solvation and entropic contributions were the most relevant for the reaction involving the formation of [EuGd]s and [GdTb]s. These observations can provide guidelines for the rational design of new heterodinuclear lanthanide complexes with identical coordination sites.