Synthesis and photophysical properties of new Ln(III) (Ln = Eu(III), Gd(III), or Tb(III)) complexes of 1-amidino-O-methylurea

Three new solid lanthanide(III) complexes, [Ln(1-AMUH)₃] · (NO₃)₃ (1-AMUH = 1-amidino-O-methylurea; Ln = Eu(III), Gd(III), or Tb(III)) were synthesised and characterised by elemental analysis, infrared spectra, magnetic moment measurement, and electron paramagnetic resonance (EPR) spectra for Gd(III) complex. The formation of lanthanide(III) complexes is confirmed by the spectroscopic studies. The photophysical properties of Gd(III), Eu(III), and Tb(III) complexes in solid state were investigated. The Tb(III) complex exhibits the strongest green emission at 543 nm and the Eu(III) complex shows a red emission at 615 nm while the Gd(III) complex shows a weak emission band at 303 nm. Under excitation with UV light, these complexes exhibited an emission characteristic of central metal ions. The powder EPR spectrum of the Gd(III) complex at 300 K exhibits a single broad band with g = 2.025. The bi-exponential nature of the decay lifetime curve is observed in the Eu(III) and Tb(III) complexes. The results reveal them to have potential as luminescent materials.     

Photoluminescence of perovskite nanosheets prepared by exfoliation of layered oxides, K2Ln2Ti3O10, KLnNb2O7, and RbLnTa2O7 (Ln: lanthanide ion)

Luminescent perovskite nanosheets were prepared by exfoliation of single- or double-layered perovskite oxides, K2Ln2Ti3O10, KLnNb2O7, and RbLnTa2O7 (Ln: lanthanide ion). The thickness of the individual nanosheets corresponded to those of the perovskite block in the parent layered compounds. Intense red and green emissions were observed in aqueous solutions with Gd1.4Eu0.6Ti3O10- and La0.7Tb0.3Ta2O7-nanosheets, respectively, under UV illumination with energies greater than the corresponding host oxide band gap. The coincidence of the excitation spectrum and the band gap absorbance indicates that the visible emission results from energy transfer within the nanosheet. The red emission intensity of the Gd1.4Eu0.6Ti3O10-nanosheets was much stronger than that of the La0.90Eu0.05Nb2O7-nanosheets reported previously. The strong emission intensity is a result of a two-step energy transfer cascade within the nanosheet from the Ti-O network to Gd(3+) and then to Eu(3+). The emission intensities of the Gd1.4Eu0.6Ti3O10- and La0.7Tb0.3Ta2O7-nanosheets can be modulated by applying a magnetic field (1.3-1.4 T), which brings about a change in orientation of the nanosheets in solution. The emission intensities increased when the excitation light and the magnetic field directions were perpendicular to each other, and they decreased when the excitation and magnetic field were collinear and mutually perpendicular to the direction of detection of the emitted light.     

Gadolinium(III) complexes of mono- and diethyl esters of monophosphonic acid analogue of DOTA as potential MRI contrast agents: solution structures and relaxometric studies

Two new macrocyclic DOTA-like chelates containing one phosphonate pendant arm were synthesised as potential contrast agents for MRI (magnetic resonance imaging). The chelates bind to the lanthanide(III) in an octadentate manner, via four nitrogen atoms, three carboxylate and one phosphonate oxygen atoms. Solution structures of [Ln(do3ap(OEt2))(H(2)O)] and [Ln(do3ap(OEt))(H(2)O)](-) were studied using (31)P and (1)H NMR spectroscopy and SAP (square-antiprismatic)/TSAP (twisted square-antiprismatic) isomerism was observed. Depending on the nature of the lanthanide(III) ion, the lanthanide(III) complexes of H(4)do3ap(OEt) are present in solution as up to four different diastereoisomers observable with NMR. The TSAP isomer is the most abundant at the beginning of the lanthanide series and, with a decrease of the ionic radius of lanthanide(III) ions, both TSAP and SAP forms were observed. A second interconversion (SAP<-->TSAP') becomes important at the end of the series (TSAP' means the TSAP species without a coordinated water molecule). The remaining axial coordination site is occupied by one water molecule for the Gd(3+)-complex. The calculated fraction of the TSAP isomer in the gadolinium(III) complexes increases in the order [Gd(DOTA)(H(2)O)](-) < [Gd(do3ap(OEt2))(H(2)O)] < [Gd(do3ap(OEt))(H(2)O)](-) < [Gd(do3ap)(H(2)O)](2-). Gadolinium(III) complexes of phosphorus-containing chelates, generally, have the advantage of a relatively fast water exchange rate due to a greater sterical demand of the phosphorus acid moiety and of the presence of the second-sphere water shell, which also contributes to the overall relaxivity. The [Gd(do3ap(OEt2))(H(2)O)] and [Gd(do3ap(OEt))(H(2)O)](-) complexes were studied by variable-temperature (17)O NMR and (1)H NMRD. The experimental data were evaluated simultaneously with commonly used equations based on Solomon-Bloembergen-Morgan approximation, extended by a contribution of the second coordination sphere. The water exchange rates were found to be strongly dependent on the TSAP/SAP isomeric ratio and the overall charge of the complex: the monoanionic [Gd(do3ap(OEt))(H(2)O)](-) complex with TSAP molar fraction equal to 0.36 has the water exchange rate of 20 x 10(6) s(-1) (tau(M) = 50 ns) while neutral [Gd(do3ap(OEt2))(H(2)O)] complex with TSAP molar fraction 0.28 has an exchange rate equal to 4.4 x 10(6) s(-1) (tau(M) = 227 ns).     

Structural and photophysical properties of coordination networks combining [Ru(bipy)(CN)4]2- anions and lanthanide(III) cations: rates of photoinduced Ru-to-lanthanide energy transfer and sensitized near-infrared luminescence

Co-crystallization of K2[Ru(bipy)(CN)4] with lanthanide(III) salts (Ln = Pr, Nd, Gd, Er, Yb) from aqueous solution affords coordination oligomers and networks in which the [Ru(bipy)(CN)4]2- unit is connected to the lanthanide cation via Ru-CN-Ln bridges. The complexes fall into two structural types: [{Ru(bipy)(CN)4}2{Ln(H2O)m}{K(H2O)n}] x xH2O (Ln = Pr, Er, Yb; m = 7, 6, 6, respectively), in which two [Ru(bipy)(CN)4]2- units are connected to a single lanthanide ion by single cyanide bridges to give discrete trinuclear fragments, and [{Ru(bipy)(CN)4}3{Ln(H2O)4}2] x xH2O (Ln = Nd, Gd), which contain two-dimensional sheets of interconnected, cyanide-bridged Ru2Ln2 squares. In the Ru-Gd system, the [Ru(bipy)(CN)4]2- unit shows the characteristic intense (3)metal-to-ligand charge transfer luminescence at 580 nm with tau = 550 ns; with the other lanthanides, the intensity and lifetime of this luminescence are diminished because of a Ru --> Ln photoinduced energy transfer to low-lying emissive states of the lanthanide ions, resulting in sensitized near-infrared luminescence in every case. From the degree of quenching of the Ru-based emission, Ru --> Ln energy-transfer rates can be estimated, which are in the order Yb (k(EnT) approximately 3 x 10(6) sec(-1), the slowest energy transfer) < Er < Pr < Nd (k(EnT) approximately 2 x 10(8) sec(-1), the fastest energy transfer). This order may be rationalized on the basis of the availability of excited f-f levels on the lanthanide ions at energies that overlap with the Ru-based emission spectrum. In every case, the lifetime of the lanthanide-based luminescence is short (tens/hundreds of nanoseconds, instead of the more usual microseconds), even when the water ligands on the lanthanide ions are replaced by D2O to eliminate the quenching effects of OH oscillators; we tentatively ascribe this quenching effect to the cyanide ligands.     

Highly uniform and monodisperse Gd(2)O(2)S:Ln(3+) (Ln = Eu, Tb) submicrospheres: solvothermal synthesis and luminescence properties

Gd(2)O(2)S:Ln(3+) (Ln = Eu, Tb) submicrospheres were successfully prepared through a facile and mild solvothermal method followed by a subsequent heat treatment. X-ray diffraction (XRD) results demonstrate that all the diffraction peaks of the samples can be well indexed to the pure hexagonal phase of Gd(2)O(2)S. The energy dispersive spectroscopy (EDS), element analysis, and FT-IR results show that the precursors are composed of the Gd, Eu, O, S, C, H, and N elements. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results show that these spheres are actually composed of randomly aggregated nanoparticles. The formation mechanism for the Gd(2)O(2)S:Ln(3+)(Ln = Eu, Tb) spheres has been proposed on an isotropic growth mechanism. Under ultraviolet excitation, Gd(2)O(2)S:Ln(3+)(Ln = Eu, Tb) spheres show red and green emission corresponding to the (5)D(0)→(7)F(2) transition of the Eu(3+) ions and the (5)D(4)→(7)F(5) transition of the Tb(3+) ions. Furthermore, this synthetic route may have potential applications for fabricating other lanthanide oxysulfides.     

Radiative and Nonradiative Lifetimes of Band Edge States and Deep Trap States of CdS Nanoparticles Determined by Time-correlated Single Photon Counting

Emission lifetimes of band edge and deep trap states of CdS nanoparticles with different surface capping were measured using time-resolved single-photon-counting^[1]. For unpassivated nanoparticles with low fluorescence yield, the emission is dominated by deep trap states and the decay can be fit to a single exponential with a time constant of 5 ns that is independent of excitation intensity. For surface passivated nanoparticles with strong luminescence, the emission is dominated by band edge states and the decay is fit to a double exponential with time constants of a few ns and 50 ns. While the 50 ns decay is independent of excitation intensity, the fast component is strongly dependent on intensity. For the fast decay component, the amplitude decreases non-linearly and the time constant becomes longer (from 2.5 to 7.9 ns) as the intensity decrease. The results support the model of exciton-exciton annihilation^[2] upon trap state saturation at high excitation intensities.     

Lanthanide(III) complexes of novel mixed carboxylic-phosphorus acid derivatives of diethylenetriamine: a step towards more efficient MRI contrast agents

Three novel phosphorus-containing analogues of H(5)DTPA (DTPA = diethylenetriaminepentaacetate) were synthesised (H6L1, H5L2, H5L3). These compounds have a -CH2-P(O)(OH)-R function (R = OH, Ph, CH2NBn2) attached to the central nitrogen atom of the diethylenetriamine backbone. An NMR study reveals that these ligands bind to lanthanide(III) ions in an octadentate fashion through the three nitrogen atoms, a P-O oxygen atom and four carboxylate oxygen atoms. The complexed ligand occurs in several enantiomeric forms due to the chirality of the central nitrogen atom and the phosphorus atom upon coordination. All lanthanide complexes studied have one coordinated water molecule. The residence times (tau(M)298) of the coordinated water molecules in the gadolinium(III) complexes of H6L1 and H5L2 are 88 and 92 ns, respectively, which are close to the optimum. This is particularly important upon covalent and noncovalent attachment of these Gd(3+) chelates to polymers. The relaxivity of the complexes studied is further enhanced by the presence of at least two water molecules in the second coordination sphere of the Gd(3+) ion, which are probably bound to the phosphonate/phosphinate moiety by hydrogen bonds. The complex [Gd(L3)(H2O)](2-) shows strong binding ability to HSA, and the adduct has a relaxivity comparable to MS-325 (40 s(-1) mM(-1) at 40 MHz, 37 degrees C) even though it has a less favourable tau(M) value (685 ns). Transmetallation experiments with Zn(2+) indicate that the complexes have a kinetic stability that is comparable to-or better than-those of [Gd(dtpa)(H2O)](2-) and [Gd(dtpa-bma)(H2O)].     

Crystal structures, phase-transition, and photoluminescence of rare earth carbodiimides

Rare earth carbodiimides with the general formula RE 2(CN 2) 3 crystallize with two modifications. A monoclinic( C2/m) modification is obtained for RE = Y, Ce-Tm and a rhombohedral ( R3 c) modification for RE = Tm-Lu. The space group R3 c is confirmed by single-crystal structure determination on Lu 2(CN 2) 3 and indexed powder patterns of RE = Tm, Yb and Lu. The use of diverse chemical syntheses conditions for Tm 2(CN 2) 3 revealed the dimorphic character of this compound. In addition, pressure experiments on Tm 2(CN 2) 3 have induced a phase-transition from rhombohedral to monoclinic. This transformation comprises an increase of the coordination number of Tm from 6 to 7, and a unit-cell volume reduction in the order of 20 %. The photoluminescence behavior of lanthanide doped Gd 2(CN 2) 3:Ln samples is presented with different activators (Ln = Ce, Tb) revealing a broad band emission of Gd 2(CN 2) 3:Ce, quite similar to that of the well-known YAG:Ce.     

Ultra small Gd(2)O(3) nanoparticles: Absorption and emission properties

In this paper, we report a facile method for synthesis of ultra small (1-3nm) gadolinium oxide (Gd(2)O(3)) nanoparticles using citric acid (CA) as a capping agent. The dependence of nanoparticle (NP) size on the ratio between CA and gadolinium (Gd) is investigated. Absorption properties of the ultra small Gd(2)O(3) NPs in UV region have four characteristic peaks at 312nm, 274nm, 253nm and 228nm. Finally, we show that the Gd(2)O(3) nanoparticles synthesized by this method induce triplet emission (phosphorescence) from CA and EG in the NIR region.     

Geometric and electronic structure of lanthanide orthophosphate nanoparticles determined with X-rays

The evolution of the geometric and electronic structures within the entire series of lanthanide orthophosphate nanoparticles ( approximately 2- approximately 5 nm) has been determined experimentally with X-ray diffraction and near edge X-ray absorption fine structure spectroscopy. In particular, the interplay between electronic structure, crystal morphology, and crystal phase has been systematically studied. A missing local order in the crystal structure accompanied by multiple ion sites in the nanoparticles was revealed to be due to the small crystal size and large surface contribution. All lanthanide ions were found to be in "3+" configuration and accommodated in three different crystallization states: the larger lanthanide ions (La, Ce, Pr, Nd, Sm) in the monoclinic phase, the smaller ones (Er, Tm, Yb, Lu) in the tetragonal phase, and the intermediate lanthanide ions (Eu, Gd, Tb, Dy, Ho) in a "mixed phase" between monoclinic and tetragonal phases.     

A self-assembled complex with a titanium(IV) catecholate core as a potential bimodal contrast agent

A ditopic chelating ligand (H(6)4) that bears catechol and diethylenetriamine-N,N,N',N',N'-pentaacetate (DTPA) has been designed and shown to specifically bind lanthanide(III) ions at the DTPA core ([Ln(H(2)4)(H(2)O)](-)) and further self-assemble with titanium(IV), thereby giving rise to the formation of a supramolecular metallostar complex with a lanthanide(III)-to-titanium(IV) ratio of 3:1, [(Ln4)(3)Ti(H(2)O)(3)](5-) (Ln=La, Eu, Gd). The efficacy of the metallostar complex as a potential bimodal optical/magnetic resonance imaging (MRI) agent has been evaluated. Nuclear magnetic relaxation dispersion (NMRD) measurements for the [(Gd4)(3)Ti(H(2)O)(3)](5-) complex have demonstrated an enhanced r(1) relaxivity that corresponds to 36.9 s(-1) mM(-1) per metallostar molecule at 20 MHz and 310 K, which is a result of a decreased tumbling rate. The ability of the complex to bind to human serum albumin (HSA) was also examined by relaxometric measurements. In addition, upon UV irradiation the [(Gd4)(3)Ti(H(2)O)(3)](5-) complex exhibits broad-band green emission in the range 400-750 nm with a maximum at 490 nm. Taking into account the high relaxivity and luminescence properties, the [(Gd4)(3)Ti(H(2)O)(3)](5-) complex is a good lead compound for the development of efficient bimodal contrast agents.     

Syntheses, crystal structures and luminescent properties of new lanthanide(III) organoarsonates

The first examples of lanthanide(III) organoarsonates, Ln(L(1))(H(2)O)(3) (Ln = La (1), H(3)L(1) = 4-hydroxy-3-nitrophenylarsonic acid), Ln(L(1))(H(2)O)(2) (Ln = Nd (2), Gd (3)), and mixed-ligand lanthanide(III) organoarsonates, Ln(2)(HL(1))(2)(C(2)O(4))(H(2)O)(2) (Ln = Nd (4), Sm (5), Eu (6)), were hydrothermally synthesized and structurally characterized. Compounds 1-3 feature a corrugated lanthanide arsonate layer, in which 1D lanthanide arsonate inorganic chains are further interconnected via bridging L(1)(3-) ligands. Compounds 4-6 exhibit a complicated 3D network. The interconnection of the lanthanide(III) ions by the bridging arsonate ligand leads to the formation of a novel 3D framework with long narrow 1D tunnels along the a-axis, with the oxalate anions are located at the above tunnels and bridging with lanthanide(III) ions. Compounds 2 and 4 exhibit the characteristic emission bands of the Nd(III) ion, whereas compound 6 displays the characteristic emission bands of the Eu(III) ion. The magnetic properties of compounds 3-6 were also investigated.     

Sensitized emission from lanthanide-doped nanoparticles embedded in a semiconductor sol-gel thin film.

In(2)O(3) sol-gel thin films made with LaF(3):Ln(3+) (Ln=Er, Nd, and Eu) nanoparticles were prepared and showed sensitized emission of the lanthanide ions after In(2)O(3) matrix excitation. The excitation spectra showed an In(2)O(3) absorption band in addition to the excitation peaks of the lanthanide ions, clearly demonstrating that there is energy transfer from the In(2)O(3) matrix to Ln(3+) (Er(3+), Nd(3+), and Eu(3+)). Similarly, HfO(2) and ZrO(2) sol-gel thin films made with LaF(3):Ln(3+) nanoparticles also showed energy transfer from the semiconductor matrix to the lanthanide ions.     

Physicochemical characterization of the dimeric lanthanide complexes [en{Ln(DO3A)(H2O)}2] and [pi{Ln(DTTA)(H2O)}2]2-: a variable-temperature 17O NMR study

The Gd(III) complexes of the two dimeric ligands [en(DO3A)2] {N,N'-bis[1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecan-10-yl-methylcarbonyl]-N,N'-ethylenediamine} and [pi(DTTA)2]8- [bisdiethylenetriaminepentaacetic acid (trans-1,2-cyclohexanediamine)] were synthesized and characterized. The 17O NMR chemical shift of H2O induced by [en{Dy(DO3A)}2] and [pi{Dy(DTTA)}2]2- at pH 6.80 proved the presence of 2.1 and 2.2 inner-sphere water molecules, respectively. Water proton spin-lattice relaxation rates for [en{Gd(DO3A)(H2O)}2] and [pi{Gd(DTTA)(H2O)}2]2- at 37.0 +/- 0.1 degrees C and 20 MHz are 3.60 +/- 0.05 and 5.25 +/- 0.05 mM(-1) s(-1) per Gd, respectively. The EPR transverse electronic relaxation rate and 17O NMR transverse relaxation time for the exchange lifetime of the coordinated H2O molecule and the 2H NMR longitudinal relaxation rate of the deuterated diamagnetic lanthanum complex for the rotational correlation time were thoroughly investigated, and the results were compared with those reported previously for other lanthanide(III) complexes. The exchange lifetimes for [en{Gd(DO3A)(H2O)}2] (769 +/- 10 ns) and [pi{Gd(DTTA)(H2O)}2]2- (910 +/- 10 ns) are significantly higher than those of [Gd(DOTA)(H2O)]- (243 ns) and [Gd(DTPA)(H2O)]2- (303 ns) complexes. The rotational correlation times for [en{Gd(DO3A)(H2O)}2] (150 +/- 11 ps) and [pi{Gd(DTTA)(H2O)}2]2- (130 +/- 12 ps) are slightly greater than those of [Gd(DOTA)(H2O)]- (77 ps) and [Gd(DTPA)(H2O)]2- (58 ps) complexes. The marked increase in relaxivity (r1) of [en{Gd(DO3A)(H2O)}2] and [pi{Gd(DTTA)(H2O)}2]2- result mainly from their longer rotational correlation time and higher molecular weight.     

Judd-Ofelt intensity parameters and spectral properties of Gd2O3:Eu3+ nanocrystals

Three nonequivalent centers of Cs (A, B, and C) in monoclinic phase and C2 and S6 centers in cubic phase were identified in the Gd2O3:Eu3+ nanocrystals with spectral techniques. Size dependence in the spectra indicated that the excitations from both host and charge-transfer band (CTB) for the 5D0 --> 7F2 transition of Eu3+ ions were nearly equal for a larger size of 135 nm of the cubic phase; however, with decreasing the size to or less than 23 nm, the excitations by the CTB dominated. The variation of excitation leading to the symmetry and energy change in the C2 and S6 sites was also observed for larger particle sizes. The Judd-Ofelt intensity parameters Omega(lambda) (lambda = 2, 4) for Gd2O3:Eu3+ nanoparticles were experimentally determined. The parameters Omega(lambda) were found to significantly change with the sizes of Gd2O3:Eu3+ from nanoparticles to bulk material. With decreasing the size from 135 to 15 nm, the quantum efficiencies for 5D0 reduced from 23.6% to 4.6% due to the increasing ratio of surface to volume.     

Highly Luminescent and Thermally Stable Lanthanide Coordination Polymers Designed from 4-(Dipyridin-2-yl)aminobenzoate: Efficient Energy Transfer from Tb(3+) to Eu(3+) in a Mixed Lanthanide Coordination Compound

Herein, a new aromatic carboxylate ligand, namely, 4-(dipyridin-2-yl)aminobenzoic acid (HL), has been designed and employed for the construction of a series of lanthanide complexes (Eu(3+) = 1, Tb(3+) = 2, and Gd(3+) = 3). Complexes of 1 and 2 were structurally authenticated by single-crystal X-ray diffraction and were found to exist as infinite 1D coordination polymers with the general formulas {[Eu(L)(3)(H(2)O)(2)]}(n) (1) and {[Tb(L)(3)(H(2)O)].(H(2)O)}(n) (2). Both compounds crystallize in monoclinic space group C2/c. The photophysical properties demonstrated that the developed 4-(dipyridin-2-yl)aminobenzoate ligand is well suited for the sensitization of Tb(3+) emission (Φ(overall) = 64%) thanks to the favorable position of the triplet state ((3)ππ*) of the ligand [the energy difference between the triplet state of the ligand and the excited state of Tb(3+) (ΔE) = (3)ππ* - (5)D(4) = 3197 cm(-1)], as investigated in the Gd(3+) complex. On the other hand, the corresponding Eu(3+) complex shows weak luminescence efficiency (Φ(overall) = 7%) due to poor matching of the triplet state of the ligand with that of the emissive excited states of the metal ion (ΔE = (3)ππ* - (5)D(0) = 6447 cm(-1)). Furthermore, in the present work, a mixed lanthanide system featuring Eu(3+) and Tb(3+) ions with the general formula {[Eu(0.5)Tb(0.5)(L)(3)(H(2)O)(2)]}(n) (4) was also synthesized, and the luminescent properties were evaluated and compared with those of the analogous single-lanthanide-ion systems (1 and 2). The lifetime measurements for 4 strongly support the premise that efficient energy transfer occurs between Tb(3+) and Eu(3+) in a mixed lanthanide system (η = 86%).     

Energy Migration Upconversion in Manganese(II)‐Doped Nanoparticles

We report the synthesis and characterization of cubic NaGdF₄:Yb/Tm@NaGdF₄:Mn core–shell structures. By taking advantage of energy transfer through Yb→Tm→Gd→Mn in these core–shell nanoparticles, we have realized upconversion emission of Mn²⁺ at room temperature in lanthanide tetrafluoride based host lattices. The upconverted Mn²⁺emission, enabled by trapping the excitation energy through a Gd³⁺ lattice, was validated by the observation of a decreased lifetime from 941 to 532 μs in the emission of Gd³⁺ at 310 nm (⁶P_7/2→⁸S_7/2). This multiphoton upconversion process can be further enhanced under pulsed laser excitation at high power densities. Both experimental and theoretical studies provide evidence for Mn²⁺ doping in the lanthanide‐based host lattice arising from the formation of F^? vacancies around Mn²⁺ ions to maintain charge neutrality in the shell layer.     

The effect of the size of raw Gd(OH)3 precipitation on the crystal structure and PL properties of Gd2O3:Eu

Our experiments show that cetyltrimethylammonium bromide (CTAB) has an obvious effect on the particle size of the precipitation of Gd(OH)3. Without CTAB, the particle size of the Gd(OH)3 precipitation is about 50 nm, whereas with CTAB, the particle size is less than 5 nm. We propose a mechanism where CTAB micelles work as a catalyst for the nucleation process and result in the precipitation of 5 nm particles. These small particles, after heat treatment at 1073 K, did not result in small Gd2O3 nanoparticles of the same size, but instead, forming crystals of 30-80 nm size in both cubic and monoclinic phases. When monitoring the photoluminescence (PL) peak at 610 nm, we found that the charge transfer state (CTS) absorption amplitude of Eu-O is reduced in the mixed structures. We speculate that the mixed structures modify the surface properties of the Gd2O3:Eu nanoparticles, leading to the reduction of Eu-O CTS absorption.     

New types of blue, red or near IR luminescent phosphonate-decorated lanthanide oxalates

Hydrothermal reactions of the lanthanide chlorides with MeN(CH2CO2H)(CH2PO3H2), (H3L1) (or Me2NCH2PO3H2, H2L2) and sodium oxalate lead to seven new lanthanide oxalate phosphonate hybrids with three types of 3D network structures, namely, [Ln(C2O4){MeNH(CH2CO2)(CH2PO3H)}]0.5 H2O (Ln=Nd: 1; Eu: 2; Gd: 3), [Ln4(C2O4)5(Me2NHCH2PO3)2(H2O)4]2 H2O (Ln=La: 4, Nd: 5), [Ln3(C2O4)4(Me2NHCH2PO3)(H2O)6]6 H2O (Gd: 6, Er: 7). Their structures have been established by X-ray single-crystal diffraction. Complexes 1-3 are isostructural and feature a 3D network formed by the interconnection of 3D network of {Ln(H2L1)}2+ with 1D chains of {Ln(C2O4)}+. Complexes 4 and 5 are isostructural and feature a complex 3D network built from 3D network of lanthanide oxalate and {Ln4(HL2)2} units. The isostructural 6 and 7 form another type of 3D network composed of porous lanthanide-oxalate network inserted by 1D chains of lanthanide-oxalate phosphonate. Compounds 1, 5 and 7 are luminescent materials in the near IR region. Compounds 3 and 6 exhibit a broad blue fluorescent emission band at 451 and 467 nm, respectively. Compound 2 displays very strong and sharp emission bands at 592, 616 and 699 nm with a long luminescent lifetime of 1.13 ms.     

Ytterbium(III) Porpholactones: β‐Lactonization of Porphyrin Ligands Enhances Sensitization Efficiency of Lanthanide Near‐Infrared Luminescence

The near‐infrared (NIR) luminescence efficiency of lanthanide complexes is largely dependent on the electronic and photophysical properties of antenna ligands. Although porphyrin ligands are efficient sensitizers of lanthanide NIR luminescence, non‐pyrrolic porphyrin analogues, which have unusual symmetry and electronic states, have been much less studied. In this work, we used porpholactones, a class of β‐pyrrolic‐modified porphyrins, as ligands and investigated the photophysical properties of lanthanide porpholactones Yb‐1 a – 5 a . Compared with Yb porphyrin complexes, the porpholactone complexes displayed remarkable enhancement of NIR emission (50–120 %). Estimating the triplet‐state levels of porphyrin and porpholactone in Gd complexes revealed that β‐lactonization of porphyrinic ligands lowers the ligand T₁ state and results in a narrow energy gap between this state and the lowest excited state of Yb³⁺. Transient absorption spectra showed that Yb^III porpholactone has a longer transient decay lifetime at the Soret band than the porphyrin analogue (30.8 versus 17.0 μs). Thus, the narrower energy gap and longer lifetime arising from β‐lactonization are assumed to enhance NIR emission of Yb porpholactones. To demonstrate the potential applications of Yb porpholactone, a water‐soluble Yb bioprobe was constructed by conjugating glucose to Yb ‐ 1 a . Interestingly, the NIR emission of this Yb porpholactone could be specifically switched on in the presence of glucose oxidase and then switched off by addition of glucose. This is the first demonstration that non‐pyrrolic porphyrin ligands enhance the sensitization efficiency of lanthanide luminescence and also display switchable NIR emission in the region of biological analytes (800–1400 nm).