EuIII Ions Research Articles

Synthesis of highly sensitive and multi-response Eu-MOF, fluorescence sensing properties and anti-counterfeiting applications

A new Europium metal–organic framework (Eu-MOF), namely [Eu(dpa) (H2O)]·0.5(bpy)·4H2O}n (H4dpa = 5-(3,4-dicarboxyphenoxy) isophenic acid, bpy = protonated 4,4′-bipyridine) was synthesized and structurally characterized by elemental analyses, infrared spectroscopy, and X-ray single-crystal diffraction analyses. Eu-MOF shows a three-dimensional network structure based on EuIII ions and (dpa)4− ligands via µ4: η1, η2, η2, η2 coordination mode. Fluorescence analysis shows that Eu-MOF has excellent fluorescence sensing characteristics, which can efficiently and sensitively detect various pollutants in water: the limit of detection (LOD) of ratiometric fluorescence detection of ANI in water was 42.9 nM, which was better than the single-peak detection limit. In addition, the peak detection limits of Eu-MOF for Flu, ORN and NB were 120 nM, 27 nM and 94 nM, respectively. In addition, XPS, LUMO orbital energy level, fluorescence lifetime, ultraviolet absorption and other principles are used to explore the mechanism of fluorescence quenching. Surprisingly, Eu-MOF not only has excellent anti- counterfeiting ability and stability, can be used as anti-counterfeiting material in life, but also has good selectivity to Flu. Eu-MOF has obvious fluorescence quenching effect on Flu on paper under ultraviolet light, which can be used for rapid in situ imaging test paper of pesticide residues.

Two Windmill-Shaped Ln18 Nanoclusters Exhibiting High Magnetocaloric Effect and Luminescence

The self-assembly of the high-nuclearity Ln-exclusive nanoclusters is challenging but of significance due to its aesthetically pleasing architectures and far-reaching latent applications in magnetic cooling technologies. Herein, two novel high-nuclearity lanthanide nanoclusters were successfully synthesized under solvothermal conditions, formulated as {[Gd18(IN)20(HCOO)8(μ6-O)(μ3-OH)24(H2O)4]·4H2O}n and {[Eu18(IN)16(HCOO)8(CH3COO)4(μ6-O)(μ3-OH)24(H2O)4]·5H2O}n (abbreviated as Gd18 and Eu18, HIN = isonicotinic acid). Both of them possess novel and exquisite windmill-shaped cationic cores in the family of high-nuclearity Ln-exclusive nanoclusters. Remarkably, the adjacent second building units are interconnected into a three-dimensional (3D) metal-organic framework by IN- ligands. As expected, the abundant existence of GdIII ions endows Gd18 with a favorable magnetic entropy change at 2.0 K for ΔH = 7.0 T (-ΔSmmax = 40.0 J kg-1 K-1), and Eu18 displays the typical luminescence of EuIII ions.

Hierarchical subcomponent self-assembly of covalent triple-stranded complexes with 3d-4f vertices: luminescence and magnetic properties.

Well-defined 3d-4f heterometallic supramolecular architectures have attracted attention because of their applications in the field of luminescence and magnetism. However, covalent metallo-supramolecular discrete complexes, decorated with hetero-metallic vertices, have never been reported because of the difficulties in design and control. Herein, we report a series of covalent metallo-supramolecular discrete complexes with 3d-4f vertices synthesized by hierarchical subcomponent self-assembly of tris(2-aminoethyl)amine, 2,6-diformyl-p-cresol, and lanthanide ions (Ln) with different amines and transition metal ions. The programmable self-assembly process results in the formation of triple-stranded hetero-metallic covalent organic discrete complexes, namely 3a-3c-(Ln, Zn) (Ln = SmIII, EuIII, DyIII, YbIII and LuIII) and 3a'-(Dy, Co), which are characterized by nuclear magnetic resonance (NMR) analysis, electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), and single-crystal X-ray analysis. Photophysical investigations disclose that the organic skeleton of 3a-(Ln, Zn) exhibits an excellent sensitizing ability toward SmIII, EuIII, and YbIII ions, displaying characteristic luminescence emission in both the visible and near-infrared (NIR) regions. AC susceptibility measurements of 3a'-(Dy, Co) reveal the frequency-independent performance under zero dc field, suggesting the absence of slow relaxation of magnetization. This work offers a new approach for the fabrication of discrete metallic covalent architectures with 3d-4f vertices.

Six-coordinated rare earth organoarsinate complexes: Crystal structure, luminescent and magnetic properties investigation

An isostructural series of rare earth complexes has been synthesized by using the dimethylarsinate ligand. All complexes have the formula [Ln(Me2AsO2)3][H2O]8 (Ln ​= ​Sm(1), Eu(2), Gd(3), Tb(4), Dy(5), Ho(6), Er(7), Tm(8), Yb(9), Y(10)). They are the first rare earth complexes ligated by organoarsinate. Crystallographic characterizations reveal that all the compounds feature 1D chain-like arrangements, in which two rare earth ions are bounded by three dimethylarsinate ligands (syn,syn, μ2-ƞ1:ƞ1) and the rare six-coordinated rare earth ions display ideal octahedron coordination geometry. The solid state photoluminescent studies reveal that compounds 2 and 4 exhibit the characteristic emission band of the EuIII and TbIII ions respectively. Magnetic measurements indicate Gd(3) shows magnetocaloric effect (MCE) with entropy change of 24.92 ​J ​kg–1 K–1 for ΔH ​= ​0 – 7 ​T at 3 ​K. The Dy(5) and Yb(9) show field induced slow relaxation, which is rare for octahedron coordinate LnIII compounds.

Tribo-Excited Chemical Reaction Using an EuIII Complex with a Stacked Anthracene Framework.

A spin-selective tribo-chemical reaction using a dinuclear lanthanide complex is demonstrated for the first time. The dinuclear complex is composed of two EuIII ions, hexafluoroacetylacetonato ligands, and anthracene-based phosphine oxide bridges. Single-crystal analysis revealed a face-to-face-type anthracene dimer structure in the dinuclear EuIII complex. Mechanical stimulus on the dinuclear EuIII complex induced selective formation of oxidized anthracene. The tribo-chemical reaction is based on a characteristic energy-transfer pathway for the selective formation of an excited triplet state.

Heterobimetallic metallacrown of EuIIICuII5 with 5-methyl-2-pyrazinehydroxamic acid: Synthesis, crystal structure, magnetism, and the influence of CuII ions on the photoluminescent properties

A 3d-4f heterobimetallic metallacrown with the formula of [EuCu5(5mpzHA)5(NO3)3/2(H2O)6]2·3NO3·4H2O·5CH3OH (MC1) has been prepared using the stirring method from a mixture of 5-methyl-2-pyrazinehydroxamic acid (5mpzHA), Cu(AcO)2·H2O, and Eu(NO3)3·5H2O salts in methanol under reflux, which yielded single crystals after slow solvent evaporation. Single crystal X-ray diffraction analysis shows a crown-like [EuCu5(5mpzHA)5] core with the 15-MC-5 system, with five CuII and one EuIII ions occupying the rim and the dome of the crown, respectively. Water molecules oxygen atoms and one nitrate anion fill the coordination sphere around the EuIII ion, which exhibits a MFF-9 shape. The MC1 is made up of two [EuCu5(5mpzHA)5(NO3)3/2(H2O)6] metallacrown units connected by one coordinated nitrate ion, where intramolecular hydrogen bonding interactions generate aR86(18) supramolecular macrocycle leading a two-dimensional supramolecular network. The emission and excitation spectra of MC1 show the absence of EuIII emission and f-f transitions, probably due to the paramagnetic nature of the CuII ions which play a key role in quenching the fluorescence in MC1. The observed magnetic properties are attributed to antiferromagnetic interactions among the CuII ions within the metallacrown rim plus the depopulation of EuIII excited Stark sublevels. This magnetic behavior was also supported by the EPR spectroscopy which presents a superposition of signals of the termally populated state 7F1 of EuIII and CuII ions at room temperature and a sole signal of CuII ion at 4 K.

Effects of MnII and EuIII Cation Exchange in Sepiolite‐Titanium Dioxide Nanocomposites in the Photocatalytic Degradation of Orange G

AbstractTwo primary mechanisms of titanium dioxide (TiO2) efficiency inhibition in ultraviolet (UV)‐driven photocatalytic reactions are the high recombination rate and sintering. To address these challenges, TiO2 nanocrystals were grown in‐situ onto sepiolite modified with MnII and EuIII ions. The resulting nanocomposites were characterized and evaluated for photocatalytic activity for Orange G (OG) degradation under UV irradiation. Resultant reduction in activity over Mn‐sepiolite‐TiO2 is attributed to charge‐carrier scavenging by unstable Mn and adsorption‐mediated chromophore protection by Mn‐oxyhydroxide. Dye removal over Eu‐sepiolite‐TiO2 was only slightly more efficient than over the control despite relevant Eu concentrations; potentially related to inhibited TiO2‐Eu interfacial synergy and superoxide radical scavenging. The results of this investigation corroborate prior observations that substrate cation‐exchange results in unpredictable behavior of the cations introduced during subsequent fabrication steps which may be of benefit or detriment to the final material.

Europium(III), Terbium(III), and Gadolinium(III) Oxamato-Based Coordination Polymers: Visible Luminescence and Slow Magnetic Relaxation.

The reaction of aqueous solutions of EuIII, TbIII, and GdIII ions with Na2Hpcpa [H3pcpa = N-(4-carboxyphenyl)oxamic acid] afforded three new isostructural oxamate-containing lanthanide(III) coordination polymers of general formula {LnIII2(Hpcpa)3(H2O)5·H2O}n [Ln = Eu (1),Tb (2), and Gd(3)]. Their structure is made up of neutral zigzag chains running parallel to the [101] direction where double syn-syn carboxylate(oxamate)-bridged dilanthanide(III) pairs (Ln1 and Ln2) are linked by three Hpcpa2- ligands, one of them with the μ-κ2O,O':κO″ coordination mode and the other two with the μ3-κ2O,O':κO″:κO'''. Additionally, two of those chains are interlinked through hydrogen bonding and π-π type interactions, resulting in a porous structure with channels where water molecules are hosted. The emission properties of 1 and 2 are evaluated as a function of the temperature, exhibiting an emission in red and green, respectively. The external quantum yield for 2 is approximately 7 times that obtained for 1, indicating that the oxamate ligand is a better sensitizer for TbIII ions. The temperature dependence of the dc magnetic properties of 1-3 reveals a different magnetic behavior depending on the nature of the LnIII ion. A continuous decrease of χMT occurs for 1 upon cooling, and finally χMT tends to vanish, as expected for the thermal depopulation of the six magnetic 7FJ excited states (J = 1-6) of the EuIII ion with a nonmagnetic 7F0 ground state. χMT for 2 decreases sharply with decreasing the temperature due to the depopulation of the splitted mJ levels of the 7F7 ground state of the magnetically anisotropic TbIII ion. A very weak antiferromagnetic interaction between the magnetically isotropic GdIII ions across the double carboxylate(oxamate) bridge is responsible for the small decrease of χMT at low temperatures for 3. The dynamic (ac) magnetic properties of 2 and 3 reveal a slow magnetic relaxation with very incipient frequency-dependent χM″ signals below 6.0 K (2) and frequency-dependent χM″ peaks below 10.0 K (3) under nonzero applied dc magnetic fields, being thus new examples of field-induced single molecule magnets (SMMs).

Three 3D Lanthanide coordination polymers: Synthesis, luminescence and magnetic properties

Three 3D structures coordination polymers: [Ln(C2O4)(CH3COO)(H2O)]n (Ln = Gd, Eu, Tb) featuring a three-dimensional (3D) structure were synthesized with light-weight ligands. 1Gd owing to the higher magnetic density based on the large mass ratio (metal/ligands) and 3D structures, shows good MCE with −ΔSmmax = 39.5 J kg−1 K−1 at 2 K and ΔH = 7 T. Meanwhile, the luminescence properties and luminescence decay of 2Tb and 3Eu were investigated, the results showed that 2Tb and 3Eu present characteristic emissions of EuIII and TbIII ions.

Spectroscopic evidence of preferential excitation of interfacial EuIII by interfacial energy transfer process on core@shell nanoparticles

The hierarchical core@shell nanostructure in upconversion nanoparticle (UCNP) has allowed high intensities of upconversion emission by interfacial energy transfer (IET) mechanism, which can also account for high downshifting emission intensities observed for core@shell nanostructures. It is well accepted that the emission of active ions, sensitized by IET is originated from ions located into narrow core@shell interface, which has been shown by physically separation of donor and acceptor ions in the core@shell nanostructure. Herein we have spectroscopic proof of the preferential sensitization of the ions into the core@shell interface by IET. We have analyzed the excitation and emission spectra profiles of the EuIII sensitized by GdIII ions on hierarchically structured β-NaYF4 nanoparticles. In this work, EuIII emission occurs through a downshifting mechanism that is like the last step of the energy transfer pathway from GdIII to active ions in nanostructured UCNPs as part of a known UC-IET processes. Photophysical results indicate that IET sensitizes mainly the EuIII ions located at the core@shell interface, where these ions experience a variety of distorted chemical environments. Such a non-symmetrical electrical fields results in an inomogeneous broadening of 5D0 → 7F2 transition emission band. The preferential, but not unique, sensitization of EuIII ions by energy transfer from GdIII ions located at distorted interface may shine light on the upconversion emission bands intensities observed in several works describing the IET in UCNPs and spectrocopically confirms that GdIII -mediated emission occurs spatially in a narrow core@shell interfacial region.

Self-assembled Tetranuclear EuIII Complexes with D2- and C2h-Symmetrical Square Scaffold.

Three new tetranuclear europium(III) alternating circular helicates, (2-PhRRRR/2-PhSSSS) [(R)- or (S)-Ph-Pybox]4EuIII4(BPP)6, (2-iPrRRRR/2-iPrSSSS) [(R)- or (S)-iPr-Pybox]4EuIII4(BPP)6, and (3-PhRRRR/3-PhSSSS) [(R)- or (S)-Ph-Pybox]4EuIII4(BHP)6, are presented with their structural and chiroptical characterization (BPP and BHP = bis-β-diketonates; Pybox = chiral bis(oxazolinyl) pyridine ligand). X-ray crystallographic analysis revealed that different extents of interligand-contacting interactions between bis-β-diketonates and Pybox ligands produce different bis-β-diketonates arrangements around four EuIII ions and, thus, their specific symmetry in the final tetranuclear complexes. 2-PhRRRR/2-PhSSSS and 3-PhRRRR/3-PhSSSS are recognized as D2-symmetry, while 2-iPrRRRR/2-iPrSSSS self-assemblies possess pseudo C2h-symmetry. Due to different molecular symmetry, 2-PhRRRR/2-PhSSSS and 2-iPrRRRR/2-iPrSSSS crystals display different ligands orientation in their EuIII coordination spheres. The presence of pseudo σh-mirror symmetry in 2-iPrRRRR/2-iPrSSSS promotes a pair of distinguishable EuIII geometries. All the chiral self-assemblies exhibit almost identical photoluminescence emission spectra patterns of f-f transitions in the EuIII core. The EuIII self-assemblies exhibit intense CPL with different observed |glum| values (2-PhRRRR/2-PhSSSS ∼ |0.31|, 2-iPrRRRR/2-iPrSSSS ∼ |0.08|, 3-PhRRRR/3-PhSSSS ∼ |0.31| in chloroform).

Chiral BINAPO Induced Circularly Polarized Luminescence in a Triple-Stranded Eu2L3(BINAPO)2 Helicate

Chiral lanthanide helicates with circularly polarized luminescence (CPL) properties have found potential application in bioanalyses and chirality sensing. However, the preparation of the enantiopure helicates through a coordination-directed self-assembly strategy is challenging due to the greatly labile coordination geometries of lanthanide ions. Herein, a pair of enantiopure triple-stranded EuIII helicates [(Eu2L3)(R/S-BINAPO)2] are assembled by three achiral C2-symmeric bis-β-diketones (4,4′-bis(4,4,4-trifluoro-1,3-dioxobutyl)(phenoxyl)-1,1′-biphenyl, L) helically twisting around two EuIII ions, and two chiral R/S-bis(diphenylphosphoryl)-1,1′-binaphthyl (R/S-BINAPO) as ancillary ligands. Electrospray ionization–mass spectrometry, NMR, and circular dichroism (CD) spectra confirm the formation of a pair of enantiopure chiral topological helicates (Eu2L3)(R-BINAPO)2 and (Eu2L3)(S-BINAPO)2. As expected, the helicates present strong CPL with the |glum| up to 0.09, and the higher luminescent quantum yields (QYs) of up to 51%.

Water-Stable Europium 1,3,6,8-Tetrakis(4-carboxylphenyl)pyrene Framework for Efficient C2H2/CO2 Separation.

Compound {(Me2NH2)3[Eu7(μ3-O)2(TBAPy)5(H2O)6]·12.5DMF} n (JXNU-5), constructed from the 1,3,6,8-tetrakis(4-carboxylphenyl)pyrene (TBAPy4-) ligand and one-dimensional (1D) europium carboxylate rods, is presented. JXNU-5 has a three-dimensional framework with 1D channels. The strong coordination bonds between EuIII ions with high charge densities and carboxylate O atoms as well as strong π···π-stacking interactions between pyrenes lead to a water-resistant JXNU-5, which was verified by powder X-ray diffraction and surface area measurements. The breakthrough simulations and experiments demonstrate that an efficient C2H2/CO2 (50/50 mixture) gas separation at ambient conditions was achieved with JXNU-5. The calculation results show that the dominating interactions between the absorbed C2H2 molecules and host framework are hydrogen bonds associated with the carboxylate O atoms exposed on the pores. Thus, an elegant example of a water-stable metal-organic framework for effective C2H2/CO2 separation is demonstrated.

Estimating the Individual Spectroscopic Properties of Three Unique EuIII Sites in a Coordination Polymer.

We isolated a coordination polymer with the formula [Eu3(3,5-dcba)9(H2O)(dmf)3]·2dmf, with three unique EuIII coordination sites in the asymmetric unit, with the EuIII ions bridged by 3,5-dichlorobenzoato (3,5-dcba) ligands. The coordination polymer crystallized in the triclinic space group P1̅ with unit cell dimensions a = 12.4899(15), b = 16.326(2), and c = 25.059(3) Å, α = 84.271(3)°, β = 84.832(3)°, and γ = 68.585(3)° and V = 4725.2(10) Å3. The characteristic 5D0 → 7F J ( J = 0-4) EuIII transitions were observed upon ligand-centered excitation. Emission lifetimes of 0.825 ± 0.085 and 1.586 ± 0.057 ms were observed and were attributed to the sites with coordination of water or dimethylformamide (dmf) molecules to each ion, respectively. Through a combination of spectroscopy and calculations, we determined the photophysical properties of each unique EuIII site. Energy-transfer rates ligand → EuIII were determined for each unique site using the overlapped polyhedra method. The rates depend on the coordinated water molecules and the different donor-acceptor distances. The two sites without coordinated water molecules and shortest donor-acceptor distance display the fastest energy-transfer rate ligand → EuIII, whereas the site with coordinated water molecules and longest donor-acceptor distance displays the slowest energy-transfer rate. Donor-acceptor distances were estimated computationally and were confirmed by calculating the frontier orbitals in the asymmetric units of the polymer using density functional theory.

Synthesis and crystal structure of a new polymorph of potassium europium(III) bis(sulfate) mono-hydrate, KEu(SO4)2·H2O.

The mixed-metal sulfate, KEu(SO4)2·H2O, has been obtained as a new polymorph using hydro-thermal conditions. The crystal structure is isotypic with NaCe(SO4)2·H2O and shows a three-dimensional connectivity of the tetra-hedral sulfate units with EuIII and KI ions. Tricapped trigonal-prismatic EuO9 units and square-anti-prismatic KO8 units link the SO4 tetra-hedra, building the three-dimensional structure. Topological analysis reveals the existence of two nodes with 6- and 10-connected nets. The compound was previously reported [Kazmierczak & Höppe (2010 ▸). J. Solid State Chem.183, 2087-2094] in the monoclinic space group P21/c with a similar structural connectivity and coordination environments to the present compound.

Sensitization of LnIII (Ln = Eu, Tb, Tm) Ion Luminescence by Functionalized Polycarbonate‐Based Materials and White Light Generation

We prepared pyridine‐2,6‐bis(ethyl)ester [BEP] and pyridine‐2,6‐bis(diethylamide) [BDP] polymers with polycarbonate backbones by ring‐opening polymerization of the pyridine‐bis(ethyl)ester and pyridine‐bis(diethylamide) units appended to a cyclic carbonate via a glycol chain. The polymers were characterized by FTIR, NMR, UV/Vis absorption and fluorescence spectroscopy, as well as SEC, powder XRD, DSC, and TGA. The measured glass transition temperature (Tg) of the BEP polymer was shifted from –32 °C to –7 and –8 °C after coordination of the EuIII and TbIII ions, respectively. Similarly, the Tg of the BDP polymer was shifted from –13 °C to –9 and –10 °C after coordination of EuIII and TbIII ions, respectively. Both polymers sensitized LnIII‐centered emission; the BEP polymer was the most efficient at sensitizing LnIII‐centered luminescence with an emission efficiency of 30 and 31 % for the EuIII and TbIII systems, respectively, compared to the 2 % determined for both the EuIII and TbIII BDP systems. Blue emission was observed when TmIII was used, and a system with the composition BEP1Eu1.8Tb28 led to a material with CIE coordinates (0.31, 0.33), typical of white light.

First Examples of Polynuclear Lanthanide Diethylene Glycol Based Coordination Clusters

Five lanthanide coordination clusters (CCs) [Ln7(µ3‐OH)4(deg)2(Hdeg)2(ben)11]·xCH3CN [Ln = Eu (1), Gd (2), Tb (3), Dy (4), Ho (5); H2deg = diethylene glycol, Hben = benzoic acid; x = 7 for 1–4, x = 6 for 5], with diethylene glycol and benzoic acid as ligands, have been prepared and structurally characterized. All CCs consist of a heptanuclear lanthanide core with a scarce tip‐sharing double‐butterfly topology. Magnetic measurements revealed that CC 4 exhibits slow magnetic relaxation, with an energy barrier of about 6 K, whereas CC 3 shows outstanding magnetocaloric effects, with an entropy change of 34.6 J Kg–1 K–1 at 2 K and ΔH = 7 T. The photoluminescence properties of CCs 1, 3, and 4 were also investigated, displaying intense characteristic emission spectra of EuIII, TbIII, and DyIII ions.

Triboluminescence of Lanthanide Coordination Polymers with Face-to-Face Arranged Substituents.

Luminescence upon the grinding of solid materials (triboluminescence, TL) has long been a puzzling phenomenon in natural science and has also attracted attention because of its broad application in optics. It has been generally considered that the TL spectra exhibit similar profiles as those of photoluminescence (PL), although they occur from distinct stimuli. Herein, we describe for the first time a large spectral difference between these two physical phenomena using lanthanideIII coordination polymers with efficient TL and PL properties. They are composed of emission centers (TbIII and EuIII ions), antenna (hexafluoroacetylacetonate=hfa), and bridging ligands (2,5-bis(diphenylphosphoryl)furan=dpf). The emission color upon grinding (yellow TL) is clearly different from that upon UV irradiation (reddish-orange PL) in TbIII /EuIII -mixed coordination polymers [Tb,Eu(hfa)3 (dpf)]n (Tb/Eu=1). The results directly indicate the discrete excitation processes of PL and TL.

Triboluminescence of Lanthanide Coordination Polymers with Face‐to‐Face Arranged Substituents

AbstractLuminescence upon the grinding of solid materials (triboluminescence, TL) has long been a puzzling phenomenon in natural science and has also attracted attention because of its broad application in optics. It has been generally considered that the TL spectra exhibit similar profiles as those of photoluminescence (PL), although they occur from distinct stimuli. Herein, we describe for the first time a large spectral difference between these two physical phenomena using lanthanideIII coordination polymers with efficient TL and PL properties. They are composed of emission centers (TbIII and EuIII ions), antenna (hexafluoroacetylacetonate=hfa), and bridging ligands (2,5‐bis(diphenylphosphoryl)furan=dpf). The emission color upon grinding (yellow TL) is clearly different from that upon UV irradiation (reddish‐orange PL) in TbIII/EuIII‐mixed coordination polymers [Tb,Eu(hfa)3(dpf)]n (Tb/Eu=1). The results directly indicate the discrete excitation processes of PL and TL.

The Role of Blue‐Emissive 1,8‐Naphthalimidopyridine N‐Oxide in Sensitizing EuIII Photoluminescence in Dimeric Hexafluoroacetylacetonate Complexes

Two new fluorescence molecules incorporating coordinated pyridine N‐oxide (PyNO) and the blue‐emitting 1,8‐naphthalimide (NI) chromophores, 4‐(1,8‐naphthalimido)pyridine N‐oxide (4‐NIPyNO) and 3‐(1,8‐naphthalimido)pyridine N‐oxide (3‐NIPyNO), are designed and used as ancillary ligands for constructing mixed‐ligand tris(β‐diketonate) lanthanide complexes, Ln2(hfa)6(4‐NIPyNO)2 and Ln2(hfa)6(3‐NIPyNO)3 (Ln = Eu, Gd; hfa = hexafluoroacetylacetone). Single‐crystal X‐ray diffraction crystallography analyses reveal that all the complexes adopt dimeric dinuclear structures; in each case, two LnIII ions from Ln(hfa)3 moieties are bridged by the oxygen atoms of the N‐oxide groups of 4‐NIPyNO and 3‐NIPyNO. The luminescence quantum yield experiment reveals that the introduction of the ancillary ligands results in the EuIII ions having luminescence enhancement about 13 times greater than that from hydrated Eu(hfa)3(H2O)2. The detailed photophysical determinations are carried out to gain insight into the roles of the NIPyNO ligands in enhancing EuIII luminescence. By investigating the ligand‐centered emission, it is found that both the singlet states (S) and the triplet states (T) are responsible for the energy transfer from the NIPyNO ligands to the metal center; in particular, the energy‐transfer efficiencies of the singlet states reach up to 63 % and 71 % for Eu2(hfa)6(4‐NIPyNO)2 and Eu2(hfa)6(3‐NIPyNO)3, respectively. This auxiliary‐ligand designing strategy enables the use of the blue‐emitting chromophore as a sensitizer of the luminescence from EuIII ions.