Preparation,luminescence and photofunctional performances of a hybrid layered gadolinium-europium hydroxide

The design and fabrication of rare earth ions incorporated into the inorganic/organic hybrid materials have attracted growing attention for seeking improved optical properties and photofunctional performances. In this paper, a novel hybrid composite based on the layered rare earth hydroxides was successfully prepared by the ion-exchange and intercalation chemical process. The rare earth elements in the composite contain gadolinium (Gd) and europium (Eu) and the molar ratio of Gd to Eu is kept constant at 1.9 : 0.1. Organic sodium dodecyl sulfonate and dye coumarin-3-carboxyllc acid are simultaneously incorporated into the layered rare earth hydroxides as supporting agent and light-harvesting antenna, respectively. The resulting hybrid layered rare earth hydroxides exhibit the enlarged interlayer distance with about 2.60 nm, and the chemical composition was confirmed through X-ray diffraction, carbon, hydrogen and nitrogen (CHN) elemental analysis, infrared spectroscopy, and thermogravimetric analysis. The layered solid compound shows the characteristic red emission corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ ion, and the luminescence intensity of the optimized compound is greatly enhanced as compared to its corresponding nitrate and the hybrid composite without the introduction of dye molecule. The hybrid layered rare earth hydroxides can be exfoliated into bright colloidal solution, which show superior recognition capability to Cu²⁺ ion with the distinct luminescence quenching. The large quenching constant (1.4 × 10⁴ L/mol) and low detection limit (0.35 μmol/L) are achieved for Cu²⁺ ion, implying a “turn-off” fluorescent sensor for Cu²⁺ detection. Moreover, a transparent film was prepared based on the colloidal solution and displays the typical red emission in folded shape. The new hybrid compound with enhanced luminescence and excellent photofunctional performances is expected to be applied in the fields of fluorescent sensing and flexible optical devices.     

A novel fluorescent sensor for Al~(3+) and Zn~(2+) based on a new europium complex with a 1,10-phenanthroline ligand

A new europium complex Eu(tta)₃Li(la)based on 1,10-phenanthroline derivative(Li=(2-(3,5-dimethoxyphenyl)-1 H-imidazo[4,5-f][1,10]phenanthroline),tta=2-thenoyItrifluoroacetone)was designed and synthesized.Its structure was characterized by¹H and¹³C NMR,elemental analysis,UV-vis,fluorescence spectra and single crystal X-ray diffraction.The crystal of the complex la belongs to monoclinic system with the space group P2_1/n.The europium complex la in the solid and in the solution displays the typical emission of Eu(III)ion centered at 612 nm as a result of the electric dipole transition(⁵D₀-?⁷F₂).It exhibits high quantum yield(20.42%),long lifetime(0.29 ms)and good CIE color coordinate(0.67,0.33)in solid.In addition,the complex shows high sensitivity and selectivity towards Al³⁺and Zn²⁺in methanol solution which can be attributed to the Al³⁺/Zn²⁺cation instead of Eu³⁺in the complex la.The LODs for Al³⁺and Zn²⁺were calculated to be 5.880×10^-7and 7.678×10^-8mol/L,respectively.Besides,the additions of Al³⁺and Zn²⁺express remarkable color changes from red to bright blue and ivory that can be clearly observed by the naked eye respectively.     

Structure regulation for ultra-high luminescence quantum yield lanthanide complex and simultaneous detection of cancer marker and ferrous ion

The exploitation of a highly selective and sensitive probe to detect both cancer marker and metal ion is of great importance.In this work,the "one stone two bird" agent of 1,10-phenanthroline(phen) is designed to disrupt the polymeric lanthanide MOFs(LnMOFs,[Ln(CHO_2)_3]n,Ln=Tb,la;Eu,1 b,CHO2=formic acid) {[Ln(CHO_2)_4·(C_2 H_8 N)]_n,Ln=Y,2 a;Gd,2 b;Dy,2 c,C_2 H_8 N=dimethylamine}) into a soluble mononuclear species [Ln(phen)2(NO_3)_3,Ln=Tb,3 a;Eu,3 b] as well as to provide an antenna for efficient photons absorption,resulting in an ultra-high luminescence quantum yield(QY,90%) europium complex.The luminescence QY is among the highest record of monomeric(zero-dimensional) lanthanide complexes.Furthermore,mononuclear Tb3+complex(3 a) functions as a multiplex sensor towards both Fe2+and cancer marker of 5-hydroxyindole-3-acetic acid(5-HIAA).Importantly,the limit of detection(LOD)for sensing 5-HIAA is an ultra-sensitive value of 1 × 10 s mol/L,which is even lower than that necessary for the early diagnosis of carcinoid tumors.More interestingly,sensing results in simulated urine reveals that 3 a has potential application for early diagnosis in the clinic.     

Nd~(3+)/Yb~(3+) co-doped mid-infrared luminescence fluorobromide glass with energy transfer and zero-thermal-quenching IR emission

Nd~(3+)/Yb~(3+) co-doped fluorobromide glass samples were prepared by melt quenching.The mid-infrared(MIR) luminescence of the Nd~(3+)/Yb~(3+) co-doped fluorobromide glass was investigated by Br-doping reduces the phonon state density of the matrix.The 3.9 μm MIR luminescence of the samples excited at 793 and 980 nm pump excitation was investigated in detail.There is an effective mutual energy transfer process between Nd~(3+) and Yb~(3+).It is proved under 793 nm excitation that the luminescence of Nd~(3+)at 3.9 μm is reduced by effective energy transfer from,Nd~(3+):~2 H_(11/2)→Yb~(3+):~2 F_(5/2),At the same time,it is proved that the effective energy transfer from Yb~(3+):~2 F_(5/2)→Nd~(3+):2 H_(11/2) under the excitation of 980 nm enhances the luminescence of Nd~(3+) at 3.9 μm.In addition,it is found that the samples still have good infrared(IR) luminescent properties when the temperature changes.The emission cross-sectional area and the absorption cross-sectional area are σ_(em)(3.87 × 10~(-20) cm~2) and σ_(abs)(4.25×10~(-20) cm~2).The fluorescence decay characteristics of the sample at 3.9 μm at the ~2 H_(11/2) level were investigated and the fluorescence lifetime was calculated.The gain performance of the sample was calculated and analyzed,which can reach 4.25 × 10~(-20) cm~2.Those results prove that Nd~(3+)/Yb~(3+)co-doped fluorobromide glass is the potential mid-infrared laser gain material.     

Synthesis of Long Afterglow Phosphors Doped B SrAl2O4:Eu2+, Dy3+ and Its Luminescent Properties

The long afterglow luminescent material SrAl₂O₄: Eu²⁺, Dy³⁺ was prepared by high temperature solid-state method. Effects of doped B on the luminescent properties of phosphors SrAl₂O₄: Eu²⁺, Dy³⁺ were investigated by means of excitation spectra, emission spectra and X-ray diffraction analysis. As the result, the addition of H₃BO₃ as flux promotes the growth of crystalline and reduces the synthesizing temperature, but the wavelength of emission peak of photoluminescent material did not change with the variation of H₃BO₃ content. The effect of Dy³⁺ concentration on the luminescent properties of material was investigated. It was found that the luminescence of phosphors prepared under the condition of the amount of H₃BO₃ 5% and the mole ratio of Eu/Dy = 1/7(Eu = 0.02 mole) had better luminescent property and longer afterglow time.     

Photophysical properties of a new ternary europium complex with 2-thenoyltrifluoroacetone and 5-nitro-1,10-phenanthroline

A ligand, 5-nitro-1,10-phenanthroline (phenNO2), was synthesized. Its Eu(III) complex with 2-thenoyltrifluoroacetone (HTTA) was prepared and characterized by elemental analysis, IR and 1H NMR spectra. The photophysical properties of the complex were studied in detail by using UV, luminescence spectra, luminescence lifetime and quantum yield. The complex exhibited nearly monochromatic red emission at 612 nm, a remarkable luminescence quantum yield at room temperature (36.0%) upon ligand excitation and a long 5D0 lifetime (458 μs), which indicated that the ligand phenNO2 could sensitize the luminescence of Eu(III) ion efficiently.     

Luminescence properties of rare earth complexes bonded to novel mesoporous spherical hybrid materials

YVO₄:Eu³⁺phosphors have been widely used in optoelectronic integration fields of its chemical and thermal stability.However,the excitation spectrum band of VO₄^3- is too narrow for high-efficiency luminescence,restricting its further development.Herein,flower-like and linear-like YVO₄:Eu³⁺ hollow mesoporous spheres were synthesized and connected with Eu organic ligand,to obtain a new hybrid luminescent material.The characterization...     

Luminescence study of europium（Ⅲ） tris（β-diketonato）/phosphonate complexes in chloroform

The extraction of Eu（Ⅲ） with β-diketone, HA, and monodentate or bidentate Lewis bases, B, into chloroform and the luminescence properties of the extracted species were studied. Pivaloyltrifluoroacetone, Hpta, and 2-thenoyltfifluoroacetone, Htta, were used as the β-diketones. The Lewis bases, B, were tetraethyl methylene diphosphonate, POPO, which was bidentate, and diethyl benzylphosphonate, PhPO which was monodentate. Based on the extraction data, the stability constants, log β, of the first complexes between tfis（β-diketonato）Eu（Ⅲ） and the phosphonate, EuA3B, were determined to be 6.0 for the POPO complex and 3.40 for the PhPO complex. The Eu（Ⅲ） luminescence intensity in the EuA3POPO was larger than EuA3 where A was either pta or tta at similar concentrations of Eu（Ⅲ）, while that in Eu（pta）3PhPO was stronger than EuA3; however, in Eu（tta）3PhPO, it was weaker than Eu（tta）3. The POPO functions as a sensitizer, and the PhPO functions as a quencher for the tta chelate and as a sensitizer for the pta chelate. From the lifetime and quantum yield, φ, of the Eu（Ⅲ） luminescence in the complexes as well as the observation of the extractability of Eu（Ⅲ） with the Hpta and the phosphonates and of the luminescence spectra of the complexes, it was confirmed that the extraction of Eu（Ⅲ） was remarkably enhanced with a β-diketonate and a strong Lewis base, and also the ternary complex that was formed as the extracted species, showed luminescence enhancement. This phenomenon may be due the formation of a strong bond between the Eu（Ⅲ） and the strong Lewis base leading to more hydrophobicity in the extracted species and also to more effective energy transfer from the Lewis base to the Eu（Ⅲ）. It was not significant whether the donor atoms were N or O.     

Rare earth double activated phosphors for different applications

For the purpose of development of highly energy-efficient light sources, one needs to design highly efficient green, red and yellow phosphors, which are able to absorb excitation energy and generate emissions. In this contribution, we present our results on producing some efficient phosphors with improved luminescence properties. Using double activation, energy could be transferred from one luminescent activator to the other one, resulting in more efficient or brighter device operation. Co-activators could be added to a host material to change the color of the emitted light. The incorporation of Eu³⁺ or Tb³⁺ ions into the CaWO₄ crystal lattice modified the luminescence spectrum due to the formation of the emission centers that generated the specific red and green light. Very efficient new red phosphors based on YNbO₄ and doped by Eu³⁺, Ga³⁺, Al³⁺ allowed recommending these materials as good candidates for different applications including LED and X-ray intensifying screens. For double activated TAG with Ce³⁺ and Eu³⁺ and for different mole ratios of Ce/Eu, the color temperature changed from 5500 K (0.331, 0.322) up to 4200 K (0.370, 0.381) and the light became “warmer”. Application of TAG: Ce, Eu in the light emitting device showed better chromaticity coordinates of luminescence and color rendering index of LEDs.     

Luminescence modification of Eu3+-activated molybdate phosphor prepared via co-precipitation

Eu-activated CaMoO4 phosphors were co-precipitated in an aqueous solution, and NH3·H2O, NH4HCO3 and (NH2)2CO as pre-cipitating aid agents were compared based on the morphology and particle size distribution of the phosphor samples. Sm3+ as sensitizer ion was investigated on the luminescence of CaMoO4:Eu, and it could strengthen the 406 nm absorption of this phosphor. At last, the scheelite CaMoO4:Eu and wolframite ZnMoO4:Eu were selected to compare their host absorption. The result showed that the scheelite molybdate host exhibited stronger UV absorption than wolframite one.     

Flexible double narrowband near-infrared photodetector based on PMMA/core-shell upconversion nanoparticle composites

Flexible narrowband near infrared(NIR)photodetectors(PDs)are urgently in demand in the fastdeveloping era of flexible electronics,due to their crucial roles in various innovative applications.Hence,we designed and synthesized the core-shell structured NaYF4:Yb³⁺,Er³⁺@NaYF4:Nd³⁺upconversion nanoparticles(UCNPs),which can be pumped by the 808 and 980 nm lights.The upconversion luminescence(UCL)are significantly enhanced after being assembled with the opal photonic crystals(OPCs)due to the photonic crystal effect,with 55 and 48 folds of enhancement factors under illuminations of 808 and 980 nm lights,respectively.Based on this hybrid,the flexible narrowband PDs were successfully fabricated on the PET substrate with the structure of OPCs/NaYF4:Yb³⁺,Er³⁺@Nd³⁺/MAPbl3,which displays excellent detection performance to double narrowband NIR light(808 and 980 nm)benefiting from the amplified UCL,with responsivity of 8.79 and 7.39 A/W,detectivity of 3.01×10¹¹and2.68×10¹¹cm·Hz^1/2/W for 808 and 980 nm lights detection respectively,along with short response time in the range of 120-160 ms.Furthermore,the OPCs/NaYF4:Yb³⁺,Er³⁺@NaYF4:Nd³⁺/MAPbI3 double narrowband PDs display low photodetection power threshold(0.05 W/cm2),outstanding flexibility,prominent moisture resistance,and good long-time stability.This work displays a new concept of narrowband NIR PDs,which open a new field for specific NIR light detections.     

Luminescent properties of Eu~（3＋） doped Gd_2WO_6 and Gd_2（WO_4）_3 nanophosphors prepared via co-precipitation method

Eu3+ doped Gd2WO6 and Gd2(WO4)3 nanophosphors with different concentrations were prepared via a co-precipitation method. The structure and morphology of the nanocrystal samples were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The emission spectra and excitation spectra of samples were measured. J-O parameters and quantum efficiencies of Eu3+ 5D0 energy level were calculated, and the concentration quenching of Eu3+ luminescence in different matrixes were studied. The results indicated that effective Eu3+:5D0-7F2 red luminescence could be achieved while excited by 395 nm near-UV light and 465 nm blue light in Gd2WO6 host, which was similar to the familiar Gd2(WO4)3:Eu. Therefore, the Gd2WO6:Eu red phosphors might have a potential application for white LED.     

Synthesis and optical properties of novel double perovskite Ca_2MgTeO_6:Dy~(3+),Na~+ phosphors for white LEDs

Novel yellow-emitting phosphors of Dy~(3+)-doped double perovskite Ca_2 MgTeO_6 were synthesized by using a conventional high-temperature solid-state reaction.The phase purity,particle morphology,size distribution,elemental composition,luminescence properties,and luminescence decay curves of the resulting products were then analyzed in detail.The Ca2 MgTeO_6:Dy~(3+),Na~+ phosphors show three emission peaks after near-ultraviolet excitation at 350 nm,which correspond to ~4 F_(9/2)→~6 H_(11/2),~4 F_(9/2)→~6 H_(13/2),and ~4 F_(9/2)→~6 H_(13/2) transitions,respectively.Among them,the strongest peak is observed at 573 nm.The best doping content of Dy~(3+)in Ca_2 MgTeO_6:xDy~(3+),xNa~+ phosphors is x=5 mol%.The calculated critical distance of energy transfer between Dy~(3+) ions is 1.6 nm.Luminescence quenching is confirmed to be due to dipole-dipole interactions among Dy~(3+) ions.The phosphors show excellent thermal stability with high activation energy(0.27 eV).The Commission Internationale de l'Eclairage(CIE) chromaticity coordinates of the Ca_2 MgTeO_6 Dy~(3+),Na~+ phosphors are located in the yellow region.White light-emitting diodes(w-LEDs) were fabricated with a high color rendering index(R_a) of 88 and a good correlated color temperature(CCT) of 5440 K.All observed properties indicate that Ca_2 MgTeO_6:Dy~(3+),Na~+ phosphors have potential applications in display and photonic devices.     

High pressure luminescence studies of europium doped GaN

We reported on the high pressure luminescence spectra of polycrystalline Eu-doped GaN material synthesized in the reaction between alloys of gallium, bismuth and europium in ammonia atmosphere. The integrated luminescence intensity of the dominant Eu³⁺ ion transition (⁵D₀→⁷F₂) at 622 nm increased approximately one order of magnitude whereas its spectral position and line width did not change significantly between ambient and 6.8 GPa pressure, respectively. Moreover, material was characterized with photo- and cathodo-luminescence, and photoluminescence excitation spectra at different temperatures. It was found that the Eu³⁺ ions occupying substitutional Ga site created different centers which could be effectively excited with above band gap excitation and from excitons resonantly photoexcited at the I₂ bound exciton energy. Furthermore, the less efficient Eu³⁺ ions excitation path existed through intrinsic impurities and defects generating shallow energy levels in the forbidden gap. It was proposed that reduction of the thermal quenching and consequent enhancement of Eu³⁺ ion emission intensity resulted from stronger localization of bound exciton on RESI trap induced by applied pressure.     

Synthesis of mesoporous core-shell structured GdPO_4:Eu@SiO_2@mSiO_2 nanorods for drug delivery and cell imaging applications

Mesoporous GdPO_4:Eu@SiO_2@mSiO_2 core-shell nanorods(NRs) were prepared by a facile two-step method.First,the monodispersed GdPO_4:Eu NRs were obtained on a large scale via a facile precipitation method,then mesoporous silica was wrapped onto their surface through hydrolysis of tetraethylorthosilicate(TEOS).The XRD result indicates that the as-prepared GdPO_4:Eu NRs core has hexagonal phase.The FTIR and the N_2 adsorption/desorption isotherm analysis confirm the successful coating of mesoporous silica.The TEM images show that the obtained GdPO_4:Eu@SiO_2@mSiO_2 NRs exhibit uniform monodisperse core-shell structure with a nanorod core(length of 200 nm;width of 20 nm),and mesoporous silica shell of 15 nm.Under excitation of 274 nm,GdPO_4:Eu@SiO_2@mSiO_2 NRs show strong red luminescence from ~5 D_0→~7 F_J(J=1,2,3 and 4) transitions of Eu~(3+).Furthermore,the GdPO_4:Eu@-SiO_2@mSiO_2 NRs exhibit obvious T_1 enhancement effect due to paramagnetism of Gd~(3+).The drug loading capacity and pH-sensitive releasing behavior of the as-prepared GdPO_4:Eu@SiO_2@mSiO_2 NRs were studied by using doxorubicin(DOX) as model drug.The excellent biocompatibility of GdPO_4:Eu@-SiO_2@mSiO_2 NRs was demonstrated by MTT assay.Taken together,the mesoporous GdPO_4:Eu@-SiO_2@mSiO_2 NRs may be potentially applied in fields of drug delivery and dual-modal imaging.     

Detection of 2,4,6-trinitrophenol based on f-f transition of Eu~(2+)

In this paper,we designed Eu~(2+)-doped BaAlF_5 and BaSiF_6 downconversion nanophosphors with strong f-f transition emission to realize the quantitative detection of TNP.The surface of the as-prepared nanophosphors was modified by polyethylenimine(PEI) to increase the water solubility and to provide a pair of electrons to bind to the benzene ring in TNP,forming a Meisenheimer complex.The detection principle of TNP is based on luminescence resonance energy transfer(LRET) technology,where the PEI-functionalized BaAlF_5:Eu~(2+) and BaSiF_6:Eu~(2+) nanophosphors are used as energy donors and TNP is an energy acceptor.With increasing TNP concentrations,the luminescence intensity of the BaAlF_5:Eu~(2+)and BaSiF_6:Eu~(2+) nanophosphors at 359 nm [~4 f_7(~6 P_(7/2))→~4 f_7(~8 S_(7/2)) transition of Eu~(2+)] displays dramatic luminescent quenching.The BaAlF_5:Eu~(2+)@PEI or BaSiF_6:Eu~(2+)@PEI nanophosphor downconversion luminescent sensors show great sensitivity and selectivity and good linearity,and the detection limits of TNP are 0.57 and 2.82 ng/mL,respectively.     

Glass forming regions and concentration-dependent luminescence properties of Tb3+-activated tellurium-lutetium-tungsten glasses

The glass-forming regions of tellurium-gadolinium-tungsten ternary system prepared at 1000℃for 60 min were firstly determined.To improve density,the full replacement of lutetium for gadolinium to form Tb³⁺-activated tellurium-lutetium-tungsten glasses with the composition of 64 TeO₂-20 WO₃-(16-y)Lu₂O₃-yTb₂O₃were designed for scintillation application.The concentration-dependent optical properties of Tb³⁺-activated tellurium-lutetium-tungsten glasses were fully investigated by transmittance,excitation and emission spectra,together with the luminescence decay curves.The energy transfer mechanism was discussed according to Huang’s rule.The optimized 4 mol%Tb₂O₃activated tellurium-lutetium-tungsten glasses with the density of 6.49 g/cm³and the lifetime of 0.551 ms are developing to be suitable for the potential detection of slow events in the future work.     

Shape control over microwave hydrothermally grown Y2O3:Eu by europium concentration adjustment

Two-step synthesis of Y2〇3:Eu nanostructures was performed. It includes microwave driven hydrothermal and calcination stages. Performed route results in crystallization of Y4〇(OH)g(N〇3):Eu crystals initially, then Y2〇3:Eu crystals after calcination. Arranged Eu contents in relation to overall cation quantity were set to 2 mol%, 10 mol% and 20 mol%. Varying europium concentrations influence habit of obtained Y4〇(OH)g(N〇3):Eu crystals from needle-like to plate-like and as a result, also shapes of final Y2〇3:Eu nanostructures. Additionally, certain amount of Eu2+ ions was detected in as-grown material using laser spectroscopy and decay kinetics measurements. Obtained material was calcined at 1200 °C in the air, which results in oxidation of Eu2+ ions and crystallization of small number of cubic EU2 O3 nanocrystals. Characterization of obtained materials was performed using XRD, SEM, TEM, EDX, CL,Raman and photoluminescence spectroscopy.     

Luminescence properties of calcium tungstate activated by lanthanide(Ⅲ) ions

Calcium tungstate phosphors activated by the Ln3+ ions(Ln=Pr, Nd, Tb, Yb) were synthesized by a traditional high-temperature solid-state method. The crystal structures and morphologies of the products were characterized by scanning electron microscopy(SEM), X-ray powders diffraction(XRD) and infrared spectra(FT-IR). The samples were found to show luminescence properties(down-conversion, DC, at excitation wavelength 254 nm and up-conversion, UC, at excitation wavelength 980 nm). CaWO4 doped with Tb3+/Yb3+ showed green DC and UC luminescence characteristic of Tb(III) ion in the range of 470–660 nm, corresponding to the 5D4→7F6,5,4,3,2 electronic transition. CaWO4 doped with Pr3+/Yb3+ showed week blue, green and red(DC and UC) luminescence of Pr(III) ion, in the wavelength region of 450–700 nm. Emission peaks were ascribed to the 3P1→3H4,5,6, 3P0→3H4,5,6, 3P1→3F2 and 3P0→3F2 transitions, respectively. CaWO4 doped with Nd3+/Yb3+ phosphor emitted orange UC luminescence at 450–690 nm(2P3/2→4I15/2, 4G7/2→4I9/2,11/2,13/2) and strong near-infrared UC luminescence at 720–900 nm(4F7/2+4S3/2→4I9/2, 4F5/2+2H3/2→4I9/2, 4F3/2→4I9/2) which is the characteristic of Nd(III) ion.     

Lanthanide complexes-functionalized ordered mesoporous TiO2: Multicolor emission (visible and near-infrared luminescence) based on visible-light sensitization

Recently, much attention has been paid to the lanthanide luminescent materials based on the visible-light sensitization for their potential applications in the fields of bio-imaging and optical devices. In this work, the lanthanide complexes have been covalently bonded to the ordered mesoporous titania (OMT) matrix, and the resulting titania-based hybrid ordered mesoporous materials (named as LnDB-OMT, Ln = Eu, Sm, Yb, Nd) were characterized by using Fourier-transform infrared (FT-IR) spectroscopy, small-angle X-ray powder diffraction (SAXD), N₂ adsorption–desorption isotherms, transmission electron microscopy (TEM), fluorescence spectroscopy, and thermogravimetric analysis. Generally, exciting with visible light is advantageous over UV excitation. Of importance here is that, under excitation with visible light, the LnDB-OMT all show characteristic visible (Eu³⁺, Sm³⁺) as well as near-infrared (Sm³⁺, Yb³⁺, Nd³⁺) luminescence of the corresponding Ln³⁺ ions (multicolor emission covered from 500 to 1400 nm spectral region), which is attributed to the energy transfer from the ligands to the Ln³⁺ ions via an antenna effect.