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 lanthanide^III coordination polymers with efficient TL and PL properties. They are composed of emission centers (Tb^III and Eu^III 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 Tb^III/Eu^III-mixed coordination polymers [Tb,Eu(hfa)₃(dpf)]_n (Tb/Eu=1). The results directly indicate the discrete excitation processes of PL and TL.     

Luminescent Europium(III) Coordination Zippers Linked with Thiophene‐Based Bridges

Novel Eu^III coordination polymers [Eu(hfa)₃(dpt)]_n (dpt: 2,5‐bis(diphenylphosphoryl)thiophene) and [Eu(hfa)₃(dpedot)]_n (dpedot: 2,5‐bis(diphenylphosphoryl)ethylenedioxythiophene) with hydrogen‐bonded zipper structures are reported. The coordination polymers are composed of Eu^III ions, hexafluoroacetylacetonato ligands, and thiophene‐based phosphine oxide bridges. The zig‐zag orientation of single polymer chains induced the formation of densely packed coordination structures with multiple intermolecular interactions, resulting in thermal stability above 300 °C. They exhibit a high intrinsic emission quantum yield (ca. 80 %) due to their asymmetrical and low‐vibrational coordination structures around Eu^III ions. Furthermore, the characteristic alternative orientation of substituents also contributes to the dramatically high ligand‐to‐metal energy transfer efficiencies of up to 80 % in the solid state.     

Metal‐Ion Sensing Europium(III) Complexes with Bidentate Phosphine Oxide Ligands Containing a 2,2′‐Bipyridine Framework

Novel Eu^III complexes with bidentate phosphine oxide ligands containing a bipyridine framework, i.e., [3,3′‐bis(diphenylphosphoryl)‐2,2′‐bipyridine]tris(hexafluoroacetylacetonato)europium(III) ([Eu(hfa)₃(BIPYPO)]) and [3,3′‐bis(diphenylphosphoryl)‐6,6′‐dimethyl‐2,2′‐bipyridine]tris(hexafluoroacetylacetonato)europium(III) ([Eu(hfa)₃(Me‐BIPYPO)]), were synthesized for lanthanide‐based sensor materials having high emission quantum yields and effective chemosensing properties. The emission quantum yields of [Eu(hfa)₃(BIPYPO)] and [Eu(hfa)₃(Me‐BIPYPO)] were 71 and 73%, respectively. Metal‐ion sensing properties of the Eu^III complexes were also studied by measuring the emission spectra of Eu^III complexes in the presence of Zn^II or Cu^II ions. The metal‐ion sensing and the photophysical properties of luminescent Eu^III complexes with a bidentate phosphine oxide containing 2,2′‐bipyridine framework are demonstrated for the first time.     

Luminescence Tuning and White‐Light Emission of Co‐doped Ln–Cd–Organic Frameworks

Four new three‐dimensional isostructural lanthanide–cadmium metal–organic frameworks (Ln–Cd MOFs), [LnCd₂(imdc)₂(Ac)(H₂O)₂]?H₂O (Ln=Pr ( 1 ), Eu ( 2 ), Gd ( 3 ), and Tb ( 4 ); H₃imdc=4,5‐imidazoledicarboxylic acid; Ac=acetate), have been synthesized under hydrothermal conditions and characterized by IR, elemental analyses, inductively coupled plasma (ICP) analysis, and X‐ray diffraction. Single‐crystal X‐ray diffraction shows that two Ln^III ions are surrounded by four Cd^II ions to form a heteronuclear building block. The blocks are further linked to form 3D Ln–Cd MOFs by the bridging imdc^3? ligand. Furthermore, the left‐ and right‐handed helices array alternatively in the lattice. Eu–Cd and Tb–Cd MOFs can emit characteristic red light with the Eu^III ion and green light with the Tb^III ion, respectively, while both Gd–Cd and Pr–Cd MOFs generate blue emission when they are excited. Different concentrations of Eu³⁺ and Tb³⁺ ions were co‐doped into Gd–Cd/Pr–Cd MOFs, and tunable luminescence from yellow to white was achieved. White‐light emission was obtained successfully by adjusting the excitation wavelength or the co‐doping ratio of the co‐doped Gd–Cd and Pr–Cd MOFs. These results show that the relative emission intensity of white light for Gd–Cd:Eu³⁺,Tb³⁺ MOFs is stronger than that of Pr–Cd:Eu³⁺,Tb³⁺ MOFs, which implies that the Gd complex is a better matrix than the Pr complex to obtain white‐light emission materials.     

Lanthanide(III) Complexes of Bis‐semicarbazone and Bis‐imine‐Substituted Phenanthroline Ligands: Solid‐State Structures,Photophysical Properties,and Anion Sensing

Phenanthroline‐based hexadentate ligands L¹ and L² bearing two achiral semicarbazone or two chiral imine moieties as well as the respective mononuclear complexes incorporating various lanthanide ions, such as La^III, Eu^III, Tb^III, Lu^III, and Y^III metal ions, were synthesized, and the crystal structures of [ML¹Cl₃] (M=La^III, Eu^III, Tb^III, Lu^III, or Y^III) complexes were determined. Solvent or water molecules act as coligands for the rare‐earth metals in addition to halide anions. The big Ln^III ion exhibits a coordination number (CN) of 10, whereas the corresponding Eu^III, Tb^III, Lu^III, and Y^III centers with smaller ionic radii show CN=9. Complexes of L², namely [ML²Cl₃] (M=Eu^III, Tb^III, Lu^III, or Y^III) ions could also be prepared. Only the complex of Eu^III showed red luminescence, whereas all the others were nonluminescent. The emission properties of the Eu derivative can be applied as a photophysical signal for sensing various anions. The addition of phosphate anions leads to a unique change in the luminescence behavior. As a case study, the quenching behavior of adenosine‐5′‐triphosphate (ATP) was investigated at physiological pH value in an aqueous solvent. A specificity of the sensor for ATP relative to adenosine‐5′‐diphosphate (ADP) and adenosine‐5′‐monophosphate (AMP) was found. ³¹P NMR spectroscopic studies revealed the formation of a [EuL²(ATP)] coordination species.     

Self‐Assembly versus Stepwise Synthesis: Heterometal–Organic Frameworks Based on Metalloligands with Tunable Luminescence Properties

A new family of heterometal–organic frameworks has been prepared by two synthesis strategies, in which IFMC‐26 and IFMC‐27 are constructed by self‐assembly and IFMC‐28 is obtained by stepwise synthesis based on the metalloligand (IFMC=Institute of Functional Material Chemistry). IFMC‐26 is a (3,6)‐connected net and IFMC‐27 is a (4,8)‐connected 3D framework. The metalloligands {Ni(H₄L)}(NO₃)₂ are connected by binuclear lanthanide clusters giving rise to a 2D sheet structure in IFMC‐28 . Notably, IFMC‐26‐Eu _x Tb _y and IFMC‐28‐Eu _x Tb _y have been obtained by changing the molar ratios of raw materials. Owing to the porosity of IFMC‐26 , Tb³⁺@IFMC‐26‐Eu and Eu³⁺@IFMC‐26‐Tb are obtained by postencapsulating Tb^III and Eu^III ions into the pores, respectively. Tunable luminescence in metal–organic frameworks is achieved by the two kinds of doping methods. In particular, the quantum yields of heterometal–organic frameworks are apparently enhanced by postencapsulation of Ln^III ions.     

The Series of Rare Earth Complexes [Ln2Cl6(μ‐4,4′‐bipy)(py)6], Ln=Y,Pr, Nd,Sm‐Yb: A Molecular Model System for Luminescence Properties in MOFs Based on LnCl3 and 4,4′‐Bipyridine

A series of 12 dinuclear complexes [Ln₂Cl₆(μ‐4,4′‐bipy)(py)₆], Ln=Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, ( 1 – 12 , respectively) was synthesized by an anhydrous solvothermal reaction in pyridine. The complexes contain a 4,4′‐bipyridine bridge and exhibit a coordination sphere closely related to luminescent lanthanide MOFs based on LnCl₃ and 4,4‐bipyridine. The dinuclear complexes therefore function as a molecular model system to provide a better understanding of the luminescence mechanisms in the Ln‐N‐MOFs ${\hbox{}{{\hfill 2\atop \hfill \infty }}}$ [Ln₂Cl₆(4,4′‐bipy)₃] ? 2(4,4′‐bipy). Accordingly, the luminescence properties of the complexes with Ln=Y, Sm, Eu, Gd, Tb, Dy, ( 1 , 4 – 8 ) were determined, showing an antenna effect through a ligand–metal energy transfer. The highest efficiency of luminescence is observed for the terbium‐based compound 7 displaying a high quantum yield (QY of 86 %). Excitation with UV light reveals typical emission colors of lanthanide‐dependent intra 4f–4f‐transition emissions in the visible range (Tb^III: green, Eu^III: red, Sm^III: salmon red, Dy^III: yellow). For the Gd^III‐ and Y^III‐containing compounds 6 and 1 , blue emission based on triplet phosphorescence is observed. Furthermore, ligand‐to‐metal charge‐transfer (LMCT) states, based on the interaction of Cl^? with Eu^III, were observed for the Eu^III compound 5 including energy‐transfer processes to the Eu^III ion. Altogether, the model complexes give further insights into the luminescence of the related MOFs, for example, rationalization of Ln‐independent quantum yields in the related MOFs.     

Systematic Investigation of Reaction‐Time Dependence of Three Series of Copper–Lanthanide/Lanthanide Coordination Polymers: Syntheses,Structures, Photoluminescence,and Magnetism

Three series of copper–lanthanide/lanthanide coordination polymers (CPs) Ln^IIICu^IICu^I(bct)₃(H₂O)₂ [Ln=La ( 1 ), Ce ( 2 ), Pr ( 3 ), Nd ( 4 ), Sm ( 5 ), Eu ( 6 ), Gd ( 7 ), Tb ( 8 ), Dy ( 9 ), Er ( 10 ), Yb ( 11 ), and Lu ( 12 ), H₂bct=2,5‐bis(carboxymethylmercapto)‐1,3,4‐thiadiazole acid], Ln^IIICu^I(bct)₂ [Ln=Ce ( 2 a ), Pr ( 3 a ), Nd ( 4 a ), Sm ( 5 a ), Eu ( 6 a ), Gd ( 7 a ), Tb ( 8 a ), Dy ( 9 a ), Er ( 10 a ), Yb ( 11 a ), and Lu ( 12 a )], and Ln^III₂(bct)₃(H₂O)₅ [Ln=La ( 1 b ), Ce ( 2 b ), Pr ( 3 b ), Nd ( 4 b ), Sm ( 5 b ), Eu ( 6 b ), Gd ( 7 b ), Tb ( 8 b ), and Dy ( 9 b )] have been successfully constructed under hydrothermal conditions by modulating the reaction time. Structural characterization has revealed that CPs 1 – 12 possess a unique one‐dimensional (1D) strip‐shaped structure containing two types of double‐helical chains and a double‐helical channel. CPs 2 a – 12 a show a three‐dimensional (3D) framework formed by Cu^I linking two types of homochiral layers with double‐helical channels. CPs 1 b – 9 b exhibit a 3D framework with single‐helical channels. CPs 6 b and 8 b display visible red and green luminescence of the Eu^III and Tb^III ions, respectively, sensitized by the bct ligand, and microsecond‐level lifetimes. CP 8 b shows a rare magnetic transition between short‐range ferromagnetic ordering at 110 K and long‐range ferromagnetic ordering below 10 K. CPs 9 a and 9 b display field‐induced single‐chain magnet (SCM) and/or single‐molecule magnet (SMM) behaviors, with U_eff values of 51.7 and 36.5 K, respectively.     

Crystal Structures of the Lanthanum(III), Europium(III), and Terbium(III) Cryptates of Tris(bipyridine) Macrobicyclic Ligands

The crystal structures of the La^III, Eu^III, and Tb^III complexes of macrobicyclic [bpy.bpy.bpy] ligands, [La³⁺ ? 1 ]3 Cl^? ( = 3- La), [Tb³⁺ ? 1 ]3 Cl^? ( = 3- Tb), and [Eu³⁺ ? 2 ]3 C1^? ( = 3- Eu), have been determined. They confirm the cryptate nature of these species, the cations being bound to the eight N-sites of the ligand. The macrobicycle presents two open faces, thus allowing additional coordination of two species, Cl^? ions or H₂O molecules, to the bound cations. These data provide structural support for the photophysical studies of the luminescent properties of the Eu^III and Tb^III cryptates, which indicated residual coordination of H₂O molecules.     

Three-dimensional porous metal-radical frameworks based on triphenylmethyl radicals

Lanthanide coordination polymers {[Ln(PTMTC)(EtOH)₂H₂O] ? x H₂O, y EtOH} [Ln=Tb ( 1 ), Gd ( 2 ), and Eu ( 3 )] and {[Ln(αH? PTMTC)(EtOH)₂H₂O] ? x H₂O, y EtOH} [Ln=Tb ( 1′ ), Gd ( 2′ ), and Eu ( 3′ )] have been prepared by reacting Ln^III ions with tricarboxylate‐perchlorotriphenylmethyl/methane ligands that have a radical (PTMTC^3?) or closed‐shell (αH? PTMTC^3?) character, respectively. X‐ray diffraction analyses reveal 3D architectures that combine helical 1D channels and a fairly rare (6,3) connectivity described with the (4².8)?(4⁴.6².8⁵.10⁴) Schäfli symbol. Such 3D architectures make these polymers porous solids upon departure of the non‐coordinated guest‐solvent molecules as confirmed by the XRD structure of the guest‐free [Tb(PTMTC)(EtOH)₂H₂O] and [Tb(αH? PTMTC)(EtOH)₂H₂O] materials. Accessible voids represent 40 % of the cell volume. Metal‐centered luminescence was observed in Tb^III and Eu^III coordination polymers 1′ and 3′ , although the Ln^III‐ion luminescence was quenched when radical ligands were involved. The magnetic properties of all these compounds were investigated, and the nature of the {Ln–radical} (in 1 and 2 ) and the {radical–radical} exchange interactions (in 3 ) were assessed by comparing the behaviors for the radical‐based coordination polymers 1 – 3 with those of the compounds with the diamagnetic ligand set. Whilst antiferromagnetic {radical–radical} interactions were found in 3 , ferromagnetic {Ln–radical} interactions propagated in the 3D architectures of 1 and 2 .     

Highly Luminescent,Water‐Soluble Lanthanide Fluorobenzoates: Syntheses,Structures and Photophysics,Part I: Lanthanide Pentafluorobenzoates

Highly luminescent, photostable, and soluble lanthanide pentafluorobenzoates have been synthesized and thoroughly characterized, with a focus on Eu^III and Tb^III complexes as visible emitters and Nd^III, Er^III, and Yb^III complexes as infrared emitters. Investigation of the crystal structures of the complexes in powder form and as single crystals by using X‐ray diffraction revealed five different structural types, including monomeric, dimeric, and polymeric. The local structure in different solutions was studied by using X‐ray absorption spectroscopy. The photoluminescence quantum yields (PLQYs) of terbium and europium complexes were 39 and 15 %, respectively; the latter value was increased almost twice by using the heterometallic complex [Tb_0.5Eu_0.5(pfb)₃(H₂O)] (Hpfb=pentafluorobenzoic acid). Due to the effectively utilized sensitization strategy (pfb)^?→Tb→Eu, a pure europium luminescence with a PLQY of 29 % was achieved.     

Three Lanthanide Metal‐Organic Frameworks Based on an Ether‐Decorated Polycarboxylic Acid Linker: Luminescence Modulation,CO2 Capture and Conversion Properties

Three new isostructural 3D lanthanide metal–organic frameworks (Ln‐MOFs), {H[LnL(H₂O)]?2 H₂O}_n ( 1‐Ln ) (Ln=Eu³⁺, Gd³⁺ and Tb³⁺), based on infinite lanthanide‐carboxylate chains were constructed by employing an ether‐separated 5,5′‐oxydiisophthalic acid (H₄L) ligand under solvothermal reaction. 1‐Eu and 1‐Tb exhibit strong red and green emission, respectively, through the antenna effect, as demonstrated through a combination of calculation and experimental results. Moreover, a series of dichromatic doped 1‐Eu_xTb_y MOFs were fabricated by introducing different concentrations of Eu³⁺ and Tb³⁺ ions, and they display an unusual variation of luminescent colors from green, yellow, orange to red. 1‐Eu with channels decorated by ether O atoms and the open metal sites displays good performance for CO₂ capture and conversion between CO₂ and epoxides into cyclic carbonates.     

Formation of Novel Dinuclear Lanthanide Luminescent Samarium(III), Europium(III), and Terbium(III) Triple‐Stranded Helicates from a C2‐Symmetrical Pyridine‐2,6‐dicarboxamide‐Based 1,3‐Xylenediyl‐Linked Ligand in MeCN

The synthesis of the C₂‐symmetrical ligand 1 consisting of two naphthalene units connected to two pyridine‐2,6‐dicarboxamide moieties linked by a xylene spacer and the formation of Ln^III‐based (Ln=Sm, Eu, Tb, and Lu) dimetallic helicates [Ln₂? 1 ₃] in MeCN by means of a metal‐directed synthesis is described. By analyzing the metal‐induced changes in the absorption and the fluorescence of 1 , the formation of the helicates, and the presence of a second species [Ln₂? 1 ₂] was confirmed by nonlinear‐regression analysis. While significant changes were observed in the photophysical properties of 1 , the most dramatic changes were observed in the metal‐centred lanthanide emissions, upon excitation of the naphthalene antennae. From the changes in the lanthanide emission, we were able to demonstrate that these helicates were formed in high yields (ca. 90% after the addition of 0.6 equiv. of Ln^III), with high binding constants, which matched well with that determined from the changes in the absorption spectra. The formation of the Lu^III helicate, [Lu₂? 1 ₃], was also investigated for comparison purposes, as we were unable to obtain accurate binding constants from the changes in the fluorescence emission upon formation of [Sm₂? 1 ₃], [Eu₂? 1 ₃], and [Tb₂? 1 ₃].     

Hybrid EuIII Coordination Luminophore Standing on Two Legs on Silica Nanoparticles for Enhanced Luminescence

In this study, we have demonstrated a two-legged, upright molecular design method for monochromatic and bright red luminescent Ln^III-silica nanomaterials. A novel Eu^III-silica hybrid nanoparticle was developed by using a doubly binding TPPO−Si(OEt)₃ (TPPO: triphenyl phosphine oxide) linker. The TPPO−Si(OEt)₃ was confirmed by ¹H, ³¹P, ²⁹Si NMR spectroscopy and single-crystal X-ray analysis. Luminescent Eu(hfa)₃ and Eu(tfc)₃ moieties (hfa: hexafluoroacetylacetonate, tfc: 3-(trifluoromethylhydroxymethylene)camphorate) were fixed onto TPPO−Si(OEt)₃-modified silica nanoparticles, producing Eu(hfa)₃(TPPO−Si)₂-SiO₂ and Eu(tfc)₃(TPPO−Si)₂-SiO₂, respectively. Eu(hfa)₃(TPPO−Si)₂−SiO₂ exhibited the higher intrinsic luminescence quantum yield (93 %) and longer emission lifetime (0.98 ms), which is much larger than those of previously reported Eu^III-based hybrid materials. Eu(tfc)₃(TPPO−Si)₂−SiO₂ showed an extra-large intrinsic emission quantum yield (54 %), although the emission quantum yield for the precursor Eu(tfc)₃(TPPO−Si(OEt)₃)₂ was found to be 39 %. These results confirmed that the TPPO−Si(OEt)₃ linker is a promising candidate for development of Eu^III-based luminescent materials.     

catena‐Poly­[[di­aqua­(isonicotinato‐O,O′)­europium(III)]‐di‐μ‐isonicotin­ato‐O:O′]

The title complex, [Eu(C₆H₄O₂)₃(H₂O)₂], has a double carboxyl­ate‐bridged infinite‐chain structure, with one chelating carboxyl­ate group on each Eu ion centre, which also binds to two water mol­ecules to yield an eight‐coordinate square‐antiprismatic geometry, with Eu—O bond lengths in the range 2.338 (3)–2.594 (3) Å. The pyridine N atoms of the isonicotinate groups do not coordinate to the Eu ions; instead, they direct the formation of Eu^III coordination polymers via hydrogen bonding with coordinated water mol­ecules.     

Long-Range LMCT Coupling in EuIII Coordination Polymers for an Effective Molecular Luminescent Thermometer**

A design for an effective molecular luminescent thermometer based on long-range electronic coupling in lanthanide coordination polymers is proposed. The coordination polymers are composed of lanthanide ions Eu^III and Gd^III, three anionic ligands (hexafluoroacetylacetonate), and a chrysene-based phosphine oxide bridges (6,12-bis(diphenylphosphoryl)chrysene). The zig-zag orientation of the single polymer chains induces the formation of packed coordination structures containing multiple sites for CH-F intermolecular interactions, resulting in thermal stability above 350 °C. The electronic coupling is controlled by changing the concentration of the Gd^III ion in the Eu^III-Gd^III polymer. The emission quantum yield and the maximum relative temperature sensitivity (S_m) of emission lifetimes for the Eu^III-Gd^III polymer (Eu:Gd=1:1, Φ_tot=52 %, S_m=3.73 % K⁻¹) were higher than those for the pure Eu^III coordination polymer (Φ_tot=36 %, S_m=2.70 % K⁻¹), respectively. Enhanced temperature sensing properties are caused by control of long-range electronic coupling based on phosphine oxide with chrysene framework.     

Comparison of the Electrochemical and Luminescence Properties of Two Carbazole‐Based Phosphine Oxide EuIII Complexes: Effect of Different Bipolar Ligand Structures

The photoluminescence (PL), electrochemical, and electroluminescence (EL) properties of Eu^III complexes, [Eu(cppo)₂(tta)₃] ( 1 ) and [Eu(cpo)₂(tta)₃] ( 2 ; TTA=2‐thenoyltrifluoroacetonate) with two carbazole‐based phosphine oxide ligands, 9‐[4‐(diphenylphosphinoyl)phenyl]‐9H‐carbazole (CPPO) and 9‐(diphenylphosphoryl)‐9H‐carbazole (CPO), which have different bipolar structures, donor–π‐spacer–acceptor (D–π–A) or donor–acceptor (D–A) systems respectively, are investigated. The CPPO with D–π–A architecture has improved PL properties, such as higher PL efficiency and more efficient intramolecular energy transfer, than CPO with the D–A architecture. Gaussian simulation proved the bipolar structures and the double‐carrier injection ability of the ligands. The carrier injection abilities of triphenylphosphine oxide, CPO, and CPPO are gradually improved. Notably, the Gaussian and electrochemical investigations indicate that before and after coordination, the carrier injection ability of the ligands show remarkable changes because of the particularity of the D‐π–A and D–A systems. The electrochemical studies demonstrate that coordination induces the electron cloud to migrate from electron‐rich carbazole to electron‐poor diphenylphosphine oxide, and consequently increases the electron‐cloud density on diphenylphosphine oxide, which weakens its ability for electron affinity and induces the elevation of LUMO energy levels of the complexes. Significantly, the π‐spacer in the D–π–A system exhibits a distinct buffer effect on the variation of the electron‐cloud density distribution of the ligand, which is absent in the D–A system. It is demonstrated that the adaptability of the D–π–A systems, especially for coordination, is stronger than that of D–A systems, which facilitates the modification of the complexes by designing multifunctional ligands purposefully. 1 seems favorable as the most efficient electroluminescent Eu^III complex with greater brightness, higher efficiencies, and more stable EL spectra than 2 . These investigations demonstrate that the phosphine oxide ligands with D–π–A architecture are more appropriate than those with D–A architecture to achieve multifunctional electroluminescent Eu^III complexes.     

Luminescence of Eu3+ and Tb3+ Complexes of Two Macrobicyclic Ligands Derived from a Tetralactam Ring and a Chromophoric Antenna

Two macrobicyclic ligands derived from an 18‐membered tetralactam ring and 2,2′‐bipyridine or 2,6‐bis(pyrazol‐1‐yl)pyridine moieties, 1 and 2 , respectively, form stable complexes with Gd^III, Eu^III, and Tb^III ions in aqueous solution. The ligand‐based luminescence is retained in the Gd^III cryptates, whereas this radiative deactivation is quenched in the Eu^III and Tb^III cryptates by ligand‐to‐metal energy transfer, resulting in the usual metal‐centered emission spectra. Singlet‐ and triplet‐state energies, emission‐decay lifetimes, and luminescence yields were measured. [Tb⊂ 1 ]³⁺ cryptate shows a long luminescence lifetime (τ=1.12 ms) and a very high metal luminescence quantum yield (Φ=0.25) in comparison with those reported in the literature for Tb³⁺ complexes sensitized by a bipyridine chromophore. By comparison to [Ln⊂ 1 ]³⁺, [Ln⊂ 2 ]³⁺ presents markedly lower luminescence properties, due to worse interaction between the 2,6‐bis(pyrazol‐1‐yl)pyridine unit and the metal ion. Moreover, the luminescent metal and the triplet ligand energy levels of [Eu⊂ 2 ]³⁺ do not match. The effects of H₂O molecules coordinated to the metal centre and of thermally activated decay processes on nonradiative deactivation to the ground‐state are also reported.     

Novel Composites of Graphitic‐phase Nitrogen Carbon/Lanthanide Coordination Polymers as White Light‐emitting Phosphor

Lanthanide coordination polymers (Ln‐CPs) are excellent candidates for designing white light materials due to their adjustable fluorescent characteristic by decorating organic ligands, changing metal centers and including guests. However, low quantum yield, weak blue emission, high prices and supply risks have hindered the application and developments of the pure Ln‐CPs materials. Herein, we have designed a new white color composite material capable of white light‐emission upon excitation at 338 nm, which fabricated by compositing a graphitic‐phase nitrogen carbon (g‐C₃N₄) treated with nitric acid and lanthanide‐based complexes, with the photoluminescencequantum yield (QY) in solid state reaching 11.7 %. WLEDs constructed by depositing the (g‐C₃N₄)_0.783/Eu_0.133/Tb_0.083‐dbpt [dbpt = 3‐(3,5‐dicarboxylphenyl)‐5‐(pyrazinyl)‐1H‐1,2,4‐triazole] composites on a commercial UV LED chip feature a CIE chromaticity coordinate at (0.33, 0.33), high color rendering index (CRI) of 94.6. Compared to conventional white light‐emission Ln‐CPs materials of La_0.928Eu_0.045Tb_0.027‐dbpt and La_0.896Eu_0.104‐dbpt reveals that (g‐C₃N₄)_0.783/Eu_0.133/Tb_0.083‐dbpt composites have higher QY and CRI values.     

Fluorescence Properties of Europium and Terbium Triundecylenate-Containing Polymers and Solutions

Europium triundecylenate, Eu(UA)₃, and terbium triundecylenate, Tb(UA)₃, were prepared by the method described in our previous paper. Either Eu(UA)₃ or Tb(UA)₃ was dissolved in methacrylic acid (<20%) and copolymerized as a crosslinker with methyl methacrylate (>80) by bulk polymerization in molds made of two glass plates. The fluorescence spectroscopy of these Eu- or Tb-containing polymers under ultraviolet/visible excitation light was investigated. The fluorescence spectroscopy of solutions of Eu(UA)₃ or Tb(UA)₃ in methacrylic acid was measured and compared with that of the solid-state Eu- or Tb-containing polymers. The fluorescence excitation and emission spectra of the solutions and polymers showed the characteristic features of free Eu³⁺ or Tb³⁺. The lifetime fluorescence of the solutions and polymers with Eu³⁺ are also included.