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The biocompatibility, bionanointeraction, uptake efficiency, and entry pathway of luminescent nanomaterials are the key factors to understand development of an efficient bionanoprobe. The foremost ...

The development of QDs based fluorescence bionanoprobe for cellular imaging fundamentally relies upon the precise knowledge of particle-cell interaction, optical properties of QDs inside and outside of the cell, movement of a particle in and out of the cell and the fate of particle. We reported engineering and physicochemical characterization of water-dispersible Eu3+/Mn2+ co-doped ZnSe@ZnS core/shell QDs and studied their potentials as bionanoprobes for biomedical applications in RAW 264.7 macrophages by evaluating their biocompatibility, fluorescence imaging capability, time-dependent uptake, endocytosis and exocytosis. The oxidation state and local atomic structure of the Eu dopant studied by X-ray absorption fine structure (XAFS) analysis manifested that the Eu3+ ions occupied sites in both ZnSe and ZnS lattices for the core/shell QDs. A novel approach was developed to relieve the excitation constraint of wide bandgap ZnSe by co-incorporation of Eu3+/Mn2+ dopants, enabling the QDs to be excited at a wide UV-visible range. The QDs displayed tunable emission colors by a gradual increase in Eu3+ concentration at a fixed amount of Mn2+, systematically enhancing the Mn2+ emission intensity via energy transfer from the Eu3+ to Mn2+ ion. The QDs presented high cell viability above 85%, inducing no cell activation. The detailed analyses of QDs treated cells by dual mode fluorescence CytoViva microscopy confirmed the systematic color-tunable fluorescence and its intensity enhances as a function of incubation time. The cells internalized the QDs predominantly via micropinocytosis and other lipid raft-mediated endocytic pathways, retaining an efficient amount for 24 h. The unique color tunability and consistent high intensity emission of QDs would be useful for developing multiplex fluorescent bionanoprobe in the wide-visible region

In this work, design and physiochemical characterization of a biocompatible nanoplatform with integrated photoluminescence and magnetic properties were reported. The potential in vivo toxicity was ...

Luminescent inorganic materials are used in several technological applications such as light-emitting displays, white LEDs for illumination, bioimaging, and photodynamic therapy. Usually, inorganic phosphors (e.g., complex oxides, silicates) need high temperatures and, in some cases, specific atmospheres to be formed or to obtain a homogeneous composition. Low ionic diffusion and high melting points of the precursors lead to long processing times in these solid-state syntheses with a cost in energy consumption when conventional heating methods are applied. Microwave-assisted synthesis relies on selective, volumetric heating attributed to the electromagnetic radiation interaction with the matter. The microwave heating allows for rapid heating rates and small temperature gradients yielding homogeneous, well-formed materials swiftly. Luminescent inorganic materials can benefit significantly from the microwave-assisted synthesis for high homogeneity, diverse morphology, and rapid screening of different compositions. The rapid screening allows for fast material investigation, whereas the benefits of enhanced homogeneity include improvement in the optical properties such as quantum yields and storage capacity.

The synthesis of persistent luminescent materials usually requires a multi-step long time annealing at high temperatures (>1200°C) in a resistive oven, causing a huge energy consumption. Also, to achieve reduced oxidation states of emitter ions (e.g., Eu3+ → Eu2+ ), the H2(g) atmosphere is often used, which can be dangerous and increase the costs of the process. Therefore, the development of a quick and new single-step green strategy, using in-situ low-risk atmosphere (e.g., CO(g)) and a microwave-assisted solid-state (MASS) method has been encouraged. In this work, we present a single-step method to synthesize the compound Sr2MgSi2O7:Eu2+,Dy3+ using the MASS method and the results were compared with those prepared by a conventional ceramic method. The luminescent material was prepared in 25 min of synthesis using carbon as a microwave susceptor and CO(g) atmosphere source at the same time. A higher concentration of Eu2+ emitter was identified by XANES in the MASS method product, which has a significant effect on the luminescence efficiency, as well as an improvement in the optical properties, leading to an emission 100 times more intense. Furthermore, to understand the Eu3+ reduction process under CO(g) atmosphere, we present here the innovative results of in-situ XANES analysis for the Sr2MgSi2O7:Eu2+,Dy3+ material. Finally, the MASS method makes it possible to prepare the materials with less than 5% of the ceramic method's duration in time. The energy-saving and better-quality persistent luminescent properties obtained in the MASS method provide viable applications on anti-counterfeiting markers, solar cell sensitizers, and other luminescent technologies.

The [Zn3(BTC)2·12H2O] (BTC = 1,3,5-tricarboxylate) metal-organic framework (MOF) was successfully synthesized using a microwave-assisted hydrothermal synthesis technique, which allowed for significantly decreased reaction time compared to the production of the same compound via conventional heating. In situ doping with Eu3+ ions at concentrations ranging from 1.0 to 5.0 mol% produced doped materials whose emission ranged from blue to red color. The Eu3+ spectroscopic properties were used to study the incorporation of the dopant into the structure of [Zn3(BTC)2·12H2O], even at very low concentrations. These experiments confirmed the usefulness of this ion as a luminescent probe, as it permitted the identification of small variations in structure not perceptible by X-ray diffraction. The variation in the coordination environment induced by increases in doping percentage was analyzed by evaluating changes in the characteristic Eu3+ excitation and emission profiles, using them to calculate luminescence lifetimes, experimental intensity parameters Ωλ (λ: 2 and 4) as well as the intrinsic quantum yield (QEu+3Eu+3) of the 5D0 emitting level of each doped MOF. The excitation and luminescence spectra show that intramolecular energy transfer from the BTC linker to Eu3+ ion, and we could observe the emission color tuning originated from the emissions of the BTC ligand and Eu3+ ion.

In the present work, new Tb3+/Eu3+ tetrakis(benzoyltrifluoroacetone) complexes containing imidazolic counterions were successfully prepared and characterized via elemental analysis, infrared spectroscopy, thermogravimetry, and X-ray powder diffraction. Photophysical features of the Eu3+ ion, such as the intrinsic emission quantum yields, radiative and non-radiative decay rates, and emission lifetimes were dramatically improved when compared with the data from the hydrated tris complex reported in the literature. The values found for the absolute emission quantum yields are up to 0.79 and ratiometric luminescent thermometers were built-up based on the ratio between the spectral areas of the 5D0 → 7F2 (Eu3+) and 5D4 → 7F5 (Tb3+) transitions. The best contactless temperature sensor operates in a wide temperature range (20–225 K) with a relative thermal sensitivity higher than 4% K−1 (maximum value of ∼7.6% K−1 at 20 K) and a temperature uncertainty lower than 0.1 K with a minimal lower than 0.01 K by combining excitation at the ligand (360 nm) and the Tb3+ ion (489 nm), illustrating the potential of lanthanide-based tetrakis complexes in the design of efficient luminescent thermometers.

This paper reports on the preparation, characterization, and photoluminescence properties of novel hybrid materials, in which the EDTA-Ln-L complexes (where L: H2 O, acac, bzac, dbm, and tta ligands, and Ln: Eu, Gd, and Tb) were covalently linked to the precursor medium molecular weight chitosan surface (CS) matrices or on the chitosan surfaces previously crosslinked with epichlorohydrin (CSech). The emission spectra of these materials were characterized by intraconfigurational-4fN transitions centred on the Eu3+ and Tb3+ ions. Some broad bands from the polymeric matrix were also observed in the emission spectra, however the relative intensities of the intraconfigurational bands increased significantly for systems containing diketonate ligands when the antenna effect became more efficient. The values of the radiative rates (Arad ) were higher for crosslinked hybrid systems with epichlorohydrin, while nonradiative rates (Anrad ) presented the opposite behaviour. These data contributed to an increase in the values of emission quantum efficiency (η) for crosslinked materials. The effect of the modification process and antenna ligand on the values of intensities, intensity parameters Ω2 e Ω4 of the Eu3+ complexes were also investigated. The results showed that the crosslinked biopolymer surfaces have great potential for applications in molecular devices light converters.

MWO4 host matrices (M: Sr, Ba) doped with different Tm3+ concentrations (0.02, 0.04, 0.06, 0.08 and 0.10 mol%) have been successfully prepared by the coprecipitation method at room temperature. The as-prepared nanophosphors were characterized by infrared spectroscopy showing intense absorption bands in the range of 700-1000 cm-1 attributed to the symmetrical and asymmetrical stretching vibrations (ν) of the tetrahedral [WO4]2- group. The X-ray diffraction (XRD) measurements reveal the tetragonal scheelite phase with the I41/a (No. 88) space group. The emission spectra of the MWO4:Tm3+ materials are dominated by the highest intensity narrow band of the intraconfigurational 1D2 → 3F4 transitions in the blue region (ca. 456 nm) arising from the Tm3+ ions. Additional low-intensity emission bands originated from the 1G4 → 3H6 (ca. 475 nm), 1G4 → 3F4 (660 nm) and 3H4 → 3H6 (700 nm) transitions are also observed. These optical results indicate that the materials can be used as an alternative to blue-emitting markers.

Eu3+ complexes and specially β-diketonate compounds are well known and studied in several areas due to their luminescence properties, such as sensors and lightning devices. A unique feature of the Eu3+ ion is the experimental determination of the 4f-4f intensity parameters Ωλ directly from the emission spectrum. The equations for determining Ωλ from the emission spectra are different for the detection of emitted power compared to modern equipment that detects photons per second. It is shown that the differences between Ωλ determined by misusing the equations are sizable for Ω4 (ca. 15.5%) for several Eu3+β-diketonate complexes and leads to differences of ca. 5% in the intrinsic quantum yields Q_Ln^Ln. Due to the unique features of trivalent lanthanide ions, such as the shielding of 4f-electrons, which lead to small covalency and crystal field effects, a linear correlation was observed between Ωλ obtained using the emitted power and photon counting equations. We stress that care should be exercised with the type of detection should be taken and provide the correction factors for the intensity parameters. In addition, we suggest that the integrated intensity (proportional to the areas of the emission band) and the centroid (or barycenter) of the transition for obtaining Ωλ should be determined in the properly Jacobian-transformed spectrum in wavenumbers (or energy). Due to the small widths of the emission bands of typical 4f-4f transitions, the areas and centroids of the bands do not depend on the transformation within the experimental uncertainties. These assessments are relevant because they validate previously determined Ωλ without the proper spectral transformation.

In this work is reported the fabrication and characterization of the triple-layer electroluminescent organic devices using a mixture of the gadolinium and europium β-diketonate complexes [GdxEuy(TTA)3 (TPPO)2] as emitting layer. The OLED devices contained the 1-(3-methylphenyl)-1,2,3,4-tetrahydroquinoline-6-carboxyaldehyde-1,1′-diphenylhydrazone (MTCD) as hole-transporting layer and tris(8-hydroxyquinoline aluminum) (Alq3) as electron transporting layer. The electroluminescence spectra present emission narrow bands from 5D1 → 7F1,2 and 5D0 → 7F0,1,2,3,4 transitions characteristics of the Eu3+ ion. These sharp lines are overlapped with a broad band attributed to the electrophosphorescence due to the T1 → S0 transition from TTA ligand. The intermolecular energy transfer from Gd-chelate to Eu-chelate is discussed based on this electrophosphorescence appearance.

[Tb(TMA):RE3+] MOFs (MOF: Metal Organic Framework; TMA: trimesic acid or 1,3,5-benzenetricarboxylic acid, RE3+: Eu and Sm) with tunable color were synthesized by aqueous coprecipitation method. Using a chemical artifice, lanthanide cationic radius contraction, it was possible to obtain only anhydrous MOFs, a very important characteristic in luminescent compounds. TMA3− anions triplet states present higher energy levels compared to the main emitting states of Eu3+ (5D0), Tb3+ (5D4) and Sm3+ (4G5/2), supplying an efficient antenna effect. Based on the spectroscopic investigation, i.e. excitation/emission spectra and lifetimes of the excited states, the material shows a high quantum efficiency (η = 83–86%) due to the very efficient energy transfer process TMA→Tb→Eu, combined to the presence of this high energy absorption ligand and the absence of water molecules.

A microwave-assisted structure-conversion (MASC) method was used to obtain photochromic hackmanites (M,Na)8Al6Si6O24(Cl,S)2 (M: Li, Na, and K) in a fast (12 to 20 min) one-step process. Structural conversion from Zeolite A to hackmanite minerals has been proven to be very effective through an aluminosilicate crystalline intermediate. Photochromism is observed with both UV and X-ray (CuKα) excitation.

Two novel luminescent europium tris ( β -diketonate) complexes [Eu(dbm) 3 ·PX] and [Eu(acac) 3 ·PX] (dbm: dibenzoylmethane, acac: acetylacetonate and PX: piroxicam) were successfully synthesized. These coordination compounds were characterized by infrared vibrational spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and luminescence spectroscopy. The thermal behavior of the complexes was investigated by thermogravimetric analysis (TG) and differential thermogravimetric analysis (DTG) techniques. The optical results have shown that these complexes present a clear intra and inter-molecular energy transfer and corroborates the sensitivity of their emission efficiency to the excitation wavelength, multiphonon non-radiative decays and temperature dependence. These new complexes may act as efficient light converting molecular devices, suggesting that they can be used for controllable photonic applications.

The synthesis of efficient nanosized persistent luminescence materials remains a challenge for the community. Paradoxically, due to the dependence of the point lattice defects and the persistent luminescence efficiency, the control of the defect formation, favorable when the materials are prepared at high temperatures, normally leads to particle growth and sintering. In this work, efficient nanosized rare earth doped disilicates Sr2MgSi2O7:Eu2+,Dy3+ were synthesized via three different wet-chemical methods taking advantages of the microwave-assisted reduction process as a support step to produce high-quality polycrystalline materials. The crystallite size of the sample showed to be smaller when the decomposition temperature of the precursors is higher and close to the phase formation energy. The excitation VUV spectroscopy indicated that despite being nanocrystalline, the materials optical band gap has just a small difference compared one to another. The reduction of Eu3+ to Eu2+ was successfully obtained, since the f-d interconfigurational transitions of Eu2+ 4f65d1→4f7 emission were observed in the blue region of the spectra. The persistent luminescence efficiency measured through its lasting decay time was close to the commercial materials references and with the advantage of having size control during the synthesis method that can lead to the size dependent applications of photonic materials.

JOYSpectra is a free-of-charge web platform to perform online calculations of spectroscopic properties of lanthanide-based compounds and materials. It has several features and functionalities to provide a detailed analysis of the intensity parameters. For instance, their dependence on the chemical environment of the lanthanide ion (Ln3+) such as structure and nature of ligating atoms, can be performed automatically and consider covalency and thermal effects. The program can also calculate the intramolecular energy transfer rates from excited donor states up to 310 transitions involving 12 Ln3+ ions. The web platform was designed to be user-friendly for experimentalists and theoreticians interested in calculations and analyses of the photophysical behavior of lanthanides. Its use requires only the structure of the compound and the choices of a few calculation options. To show its easiness and usefulness, a detailed step-by-step calculation and analysis are performed for the [Ln(tta)3(H2O)2] (Ln: Eu and Tb) complexes to explain and quantify their distinct luminescence properties.

Clay minerals are versatile materials with numerous industrial applications. Their unique layered structure can act as a host for many optically active species. The synthesis and luminescence properties of chlorohectorite clays are now reported for the first time. The synthesized clays are composed of quasi-circular nanoparticles with diameters around 20–30 nm showing blue/green emission and persistent luminescence with a duration of ca. 5 s. The luminescence features are associated with titanium impurities in the chlorohectorite structure. It is shown that Ti can act as activator ion even at low concentrations: the XRF and ICP-MS measurements of the chlorohectorite materials indicate a Ti concentration around 60 ppm originating from the precursors. The XPS measurements of the clay materials showed the Ti 2p3/2 signals at 457.8 and 458.9 eV associated with Ti3+ and TiIV, respectively. The excitation spectra confirm Ti3+ as the luminescent center in the chlorohectorites through the bands at 287 and 370 nm, related to the e − ( O 2 − ( 2 p ) ) → Ti IV charge transfer and the electronic transitions from the t2g to eg levels of Ti3+, respectively. The persistent luminescence properties are due to structural defects common for layered silicates.

In this work the synthesis, characterization and photoluminescent and electroluminescent behavior of the [Eu(DBM)₃(PTSO)₂] complex have been investigated. The emission spectrum of this Eu³⁺–β– diketonate complex show characteristics narrow bands arising from the ⁵D₀→⁷Fȷ (J = 0–4) transitions, which are split according to the selection rule for Cs, Cn or Cnv site symmetries. Triple and doublelayer organic light-emitting diodes (OLEDs) using NPB as hole transporting layer, Alq₃ as electron transporting layer and [Eu(DBM)₃(PTSO)₂] complex as emitting and electron transporting layer were grown and characterized. We found the presence of two concurrent mechanisms for the electroluminescent behavior: (1) the electroluminescence (EL) from the exciton-ligand-Eu³+ ion energy transfer, responsible for the EL narrow bands; and (2) the molecular electrophosphorescence with an initial energy transfer exciton-ligand and posterior intersystem crossing from the excited singlet S₁ to the triplet T state followed by molecular phosphorescence (T→S₀). The electroluminescent behavior of [Eu(DBM)₃(PTSO)₂] complex suggest that this complex is promising to applied at Light Conversion Molecular Devices (LCMDs) such as in OLED devices.

Undergraduate-level laboratory experiments that involve the synthesis of nanomaterials with well-defined/controlled shapes are very attractive under the umbrella of nanotechnology education. Herein we describe a low-cost and facile experiment for the synthesis of Cu(OH)2 and CuO nanowires comprising three main parts: (i) synthesis of Cu(OH)2 nanowires by a precipitation approach followed by a calcination step that converts Cu(OH)2 to CuO; (ii) use of Cu(OH)2 and CuO nanowires as model systems to explore a variety of characterization techniques relevant in the context of solid-state chemistry, materials chemistry, and nanoscience; and (iii) presentation/discussion of the data. Other learning objectives include probing of chemical transformations at the nanoscale and the use of concepts borrowed from coordination chemistry to understand the formation mechanism of Cu(OH)2 and CuO nanowires from a Cu2+(aq) precursor. This experiment can be performed with a relatively simple laboratory infrastructure and with ...

The triply-doped xTb 3+ /xEu 3+ /xDy 3+ CaWO 4 (x: 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 mol%) nanomaterials were prepared at room temperature by a coprecipitation method. The luminescence materials were characterized by X-ray powder diffraction (XPD), thermal analysis (TG), infrared absorption spectroscopy (FTIR) and UV excited photoluminescence. The prepared powder phosphors are single-phase scheelite structure with porous morphology and particle sizes around 11 nm. The materials display white color from cool to the warm white, under UV excitation, as a result of the intraconfigurational 4f transitions from trivalent rare earth ions. The non-radiative energy transfer processes from the O→W and O→Eu LMCT as well as the 4f 8 →4f 7 5d 1 states to the intraconfigurational 4f excited levels of rare earth ions and simultaneous emissions from the 4 F 9/2 (Dy 3+ )→ 5 D 4 (Tb 3+ )→ 5 D 1 , 5 D 0 (Eu 3+ ) emitter levels are reported. Furthermore, CIE parameters and the color correlated temperature (CCT) are discussed in order to characterize the color emission. Based on the results, these luminescence materials may be potential candidates for white light emitting diodes and solid-state lighting.

The preparation of novel triply-doped bifunctional Fe3O4/ZnS@LaF3:xCe3+,xGd3+,yTb3+ (x = 5; y = 5, 10 and 15 mol%) nanocomposites with efficient optical and magnetic features has been reported. The ZnS semiconductor functionalized Fe3O4 particles were coated with LaF3:RE3+ materials via a chitosan-assisted co-precipitation method. The size of iron oxide ∼7.2 nm and trigonal structures of bifunctional nanostructures were confirmed through X-ray diffraction and high-resolution transmission electron microscopy. The static magnetic measurements supported and manifested the superparamagnetic behavior of the materials at 300 K. A broad emission band was observed in the blue region (400–550 nm) due to the sulphur vacancy on the surface of the Fe3O4/ZnS nanocomposite. For a triply doped bifunctional nanostructure, the excitation spectra revealed broad absorption bands centered at around 270 nm, which were attributed to the 4f(7F7/2) → 5d interconfigurational transition of the Ce3+ ion accompanied by narrow absorption lines arising from the 4f–4f intraconfigurational transitions of the Tb3+ ion. The emission spectra of the nanocomposites showed characteristic narrow emission lines assigned to the 5D4 → 7FJ transitions (J = 6–0) of the Tb3+ ion. The energy transfer process from the Ce3+ → Gd3+ → Tb3+ ions has also been presented and discussed. Furthermore, the structural, photoluminescence and magnetic properties of Fe3O4/ZnS@LaF3:RE3+ suggested that it may be an efficient candidate for magnetic light-converting molecular devices (MLMCDs) and high energy radiation detection.

Self-supported oligo-layered ZnAlEu LDH nanotubes (∅ 20 nm) self-assemble upon controlled hydrolysis of the metal ions (Zn2+, Al3+, Eu3+) in the presence of 1,3,5-benzenetricarboxylate anions and non-ionic worm-like micelles. Their high surface area and easily accessible cylindrical mesopores (175 m2 g−1; 0.75 cm3 g−1) facilitate interaction with 5 nm CdTe quantum dots, enhancing the overall luminescence behavior.

The odd-even effect in luminescent [Eu2 (L)3 (H2 O)x ]⋅y(H2 O) complexes with aliphatic dicarboxylate ligands (L: OXA, MAL, SUC, GLU, ADP, PIM, SUB, AZL, SEB, UND, and DOD, where x=2-6 and y=0-4), prepared by the precipitation method, was observed for the first time in lanthanide compounds. The final dehydration temperatures of the Eu3+ complexes show a zigzag pattern as a function of the carbon chain length of the dicarboxylate ligands, leading to the so-called odd-even effect. The FTIR data confirm the ligand-metal coordination via the mixed mode of bridge-chelate coordination, except for the Eu3+ -oxalate complex. XRD results indicate that the highly crystalline materials belong to the monoclinic system. The odd-even effect on the 4 f-4 f luminescence intensity parameters (Ω2 and Ω4 ) is explained by using an extension of the dynamic coupling mechanism, herein named the ghost-atom model. In this method, the long-range polarizabilities ( α * ) were simulated by a ghost atom located at the middle of each ligand chain. The values of α * were estimated using the localized molecular orbital approach. The emission intrinsic quantum yield ( Q L n L n ) of the Eu3+ complexes also presented an the odd-even effect, successfully explained in terms of the zigzag behavior shown by the Ω2 and Ω4 intensity parameters. Luminescence quenching due to water molecules in the first coordination sphere is also discussed and rationalized.

In this study, a novel type of tris(2-acyl-1,3-indandione)-aluminum(III) coordination compounds of the general formula [Al(acind)3]H2O, where 2-acyl-1,3-indandione (acind), 2-acetyl-1,3-indandione (aind), 2-benzoyl-1,3-indandione (bind), and 4-methyl-2-benzoyl-1,3-indandione (mbind), were synthesized and characterized by elemental analysis (CHN), Fourier transform infrared (FTIR) and nuclear magnetic resonance (1H NMR) spectroscopies, thermal analysis (TG/DTG and DTA), and optical absorption spectroscopy in the UV-Vis region. These compounds present remarkably high green luminescence in powder and in thin-film forms. However, when these compounds are applied in glass/ITO/β-NPB/spiro-2CBP/[Al(acind)3]/Al and glass/ITO/β-NPB/[Al(acind)3]/LiF/Al electroluminescent devices, where spiro-2CBP is 2,7-bis(carbazol-9-yl)-9,9-spirobifluorene and β-NPB is N,N’-bis(naphthalen-2-yl)-N,N’-bis(phenyl)-benzidine, the emission color tuned from green to red, reflecting a change from the direct charge recombination in the emitting layer of the [Al(acind)3] complexes to an exciplex-based emission in which [Al(acind)3] complexes and spiro 2-CBP acted as acceptor and donor, respectively. These results suggest that [Al(acind)3] complexes have potential applications as molecular light converter materials for fabricating new electroluminescent devices.

Three new β-diketone–Ln-EDTA (β-diketone = TTA, BTFA, ACAC; Ln=Eu3+ and Tb3+) water-soluble complexes were prepared, and their photophysical properties were investigated in aqueous solutions and compared with the Eu–EDTA complex. A very strong red and green luminescence was observed by the addition of ligands to the aqueous solutions of the Eu–EDTA and Tb–EDTA complexes, respectively, due to the formation of water-soluble β-diketone–Ln–EDTA complexes. To confirm the formation and stoichiometry of the new β-diketone–Ln–EDTA complex, the Judd–Ofelt intensity parameters Ω2 for Eu3+ complexes and the band width at half height (Δλ) for Tb3+ complexes were used. The dependence of these parameters on the addition of the β-diketone strongly suggests that only one β-diketonate ligand is in the first coordination sphere of the β-diketone–Ln–EDTA complexes. These new Eu3+ and Tb3+ systems may act as red and green optical markers for bioassay or bioimaging.

RE2O2S:Yb3+ and RE2O2S:Yb3+,Ti,Mg2+ near-infrared persistent luminescence materials (RE3+: La, Gd, Y) were designed based on the efficient red-emitting RE2O2S:Eu3+,Ti,Mg2+, due to the similar ground state level positions between Eu3+ and Yb3+. The Y2O2S:Yb3+,Ti,Mg2+ showed the longest near-infrared (~983 nm) persistent luminescence time (~1 h) when excited at the charge transfer transition, demonstrating that Ti,Mg2+ co-doping enhances the persistent luminescence only for the Y2O2S host. The unprecedented relationship between Eu3+ and Yb3+ persistent luminescence opens a new path in the systematic design of efficient Yb3+-activated persistent luminescence materials e.g. Y2O2S:Yb3+,Ti,Mg2+, which present potential for photonic applications such as bioimaging probes.

In this work, the microwave-assisted solid-state (MASS) synthesis is reported as a rapid, cost-effective and environmental-friendly way to prepare Gd2O2S:Tb3+ X-ray scintillation standards. The preparation procedure employs active charcoal as the microwave susceptor, using a domestic microwave oven without a setup for special gases. The MASS method drastically reduced the synthesis time and energy consumption (up to 97% in nominal power) over previous reports using conventional solid-state methods. A single-step synthesis of 10 min is enough to yield highly crystalline powders starting from Gd2O3 and Tb4O7 precursors and elemental sulfur. In order to obtain 100% pure materials with superior scintillation efficiency, two microwave treatments of 25 min each are required. Due to the reducing CO atmosphere generated in situ by the active charcoal during the microwave synthesis, no Tb4+ impurity was found according to Synchrotron Radiation X-ray Absorption (SR-XAS) experiments. Spectroscopic studies were carried out using SR Vacuum-Ultraviolet (VUV) photoluminescence and SR X-ray Excited Optical Luminescence (XEOL). The material prepared by two-step synthesis exhibited a better scintillation performance owing to higher crystal purity and emission intensity, presenting versatility for technological applications such as X-ray imaging and scintillation bio-probing.

A critical review on the mechanisms and behavior of 4f intraconfigurational transitions in controllable chemical environments related to nonradiative intramolecular energy transfer processes in lanthanide chelates is presented. The term “modeling” is here used in the sense of manipulating and controlling the photophysical properties of these compounds, allowing obtaining distinguished and specific luminescent behavior. In this chapter an effort is made to show that a theoretical model, jointly used with experimental available data, is able to provide this modeling process in a comprehensive and useful way. The model allows estimating quantitatively intramolecular energy transfer rates by several mechanisms. Selection rules and the spectral overlap factor (energy mismatch conditions, for which an analytical expression is available) may be used to define relevant energy transfer pathways, and the solution (analytically or numerically) of appropriate systems of rate equations is crucial to deduce dominant pathways. Emission quantum yields, then, can be estimated and rationalized. In these rate equations all possible transition channels (radiative and non-radiative) must be included; some of them may be taken into account through the level decaying lifetime. Attempts to standardize notation is made, and some misinterpretations, perspectives and challenges on this subject are discussed.

The visible green and red upconversion luminescence hexagonal phase Er3+ and Yb3+ doped NaGdF4 nanoparticles of different sizes and morphologies were prepared through high temperature RE3+ ions/oleic acid based organometals and hydrothermal methods, respectively. Their microstructural characterizations were accomplished using X-ray powder diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy analyses. High resolution transmission electron microscopy (HR-TEM) images suggested spherical ultra-small nanocrystals of 6.4 nm for the green luminescence β-NaGdF4:Yb3+,Er3+ and oval/mostly rod shapes particles of ~ 40 nm width and ~ 100 nm length for the red emitting one. The same hexagonal (β-NaGdF4) local structure was confirmed from the selected area electron diffraction (SAED), in corroboration with XRD patterns for both sizes and shapes nanoparticles. Raman scattering result exhibited red Raman shifts of lattice peaks and anomalous line narrowing with decreasing the particle size from ~ 100 to ~ 6.4 nm. The photoluminescence spectroscopy manifested higher intensity 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 (green emission) transitions of Er3+ ion for ultra-small nanocrystals and dominant 4F9/2 → 4I15/2 (red emission) one for the large size nanorods. The change in size of the particles might be account for the observed tuning in upconversion emission.

The fabrication of bifunctional nanocomposites, co-assembling photonic (RE3+) and magnetic (Fe3O4) features into single entity nanostructures is reported through a facile method, using Fe3O4 as core nanoparticles, which were coated with SiO2 shell and further grafted with Eu3+ and Tb3+ complexes. The sophisticated structural features and morphologies of the core-shell Fe3O4@SiO2-(TTA-RE-L) nanomaterials were studied by Small-angle X-ray Scattering. The core mean size 〈 D SAXS 〉 , shell thickness Δ R , cluster size ξ and fractal dimension DF were determined by fitting the experimental SAXS data, corroborating through Transmission Electron Microscopy images. The DC magnetic properties at temperatures of 2 and 300 K were explored in support to the structural conclusions from SAXS and TEM analyses. The magnetic contributions of the RE3+ ions to the magnetizations of the Eu3+ and Tb3+ nanocomposites were discussed. The photoluminescence properties of the Eu3+ and Tb3+ nanocomposites based on the emission spectral data and luminescence decay curves were studied. The experimental intensity parameters (Ωλ), lifetimes (τ), emission quantum efficiencies (η) as well as radiative (Arad) and non-radiative (Anrad) decay rates were calculated and discussed, in addition, the structural conclusions from the values of the 4f-4f intensity parameters in the case of the Eu3+ ion. These novel Eu3+ and Tb3+ nanocomposites may act as red and green emitting layers for magnetic and light converting molecular devices.

Rare earth silicate based MnMgSi2O5+n (M = Ca, Sr or Ba and n=1-2) phosphors, have attracted interest of researchers due to their high efficiency as a host, excellent thermal and chemical stability and high brightness adding to their low cost. These phosphors showed great potential in various applications such as fluorescent lamps, white light emitting diodes, and display components. High temperature solid-state reactions are usually employed to synthesize those compounds. This paper proposes an alternative method of obtaining nanophosphor host based on Eu-doped CaMgSi2O6 (CMS:Eu), persistent luminescence phosphor. Sol gel technique combined to a modified molten salt method was used. The resulted powder was calcined for 3h under an atmosphere of 5% H2 and 95% Ar2. Phase identification by XRD and the measurements of photoluminescence (PL) and photoluminescence excitation (PLE) were performed. Single phased CMS:Eu with persistent luminescence characteristics was prepared.

The thermodynamic properties of the fabrication of NiTiO3 material in different reaction times are reported. The design of this material is accessible through a new efficient sol–gel methods, utilizing Ni(Ac)2·4H2O and Ti(OiPr)4 as starting materials for the formation of NiTiO3 final product through thermal decomposition. The thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques were used to analyze the reaction of Ni(Ac)2·4H2O and Ti(OiPr)4, which produces precursor materials at 0.5, 1, 2, 24, 48 and 72 h of reaction times, as well as the thermal stability of these precursors and the final product. The DSC data show an exothermic phenomenon of releasing large amount of energy of −1393 J/g at T Peak 655 K due to the first event of decomposition started at T Onset 607 K and finished at T Endset 663 K for the precursor materials obtained at 0.5 h of reaction, showing the presence of starting materials in this precursor. A similar exothermic behavior was observed in the sample of 1 h of reaction time and was vanished in the materials obtained at 2–72 h of reaction, indicating the influence of the time on the completion of reaction and formation of NiTiO3 crystalline phase as final product of thermal decomposition. In addition, using the information obtained from the TG/DSC, XRD and FTIR analyses, the optimum temperature for the thermal decomposition of the precursor materials to NiTiO3 with fairly high crystallinity was also determined and discussed.

The yellow emitting dysprosium oxysulfide (Dy2O2S) and dysprosium oxysulfate (Dy2O2SO4) compounds were prepared from the thermal decomposition of hydrated dysprosium sulphate. The materials were characterized by using thermogravimetry (TG/DTG), X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopies. The thermal stability temperatures at around 1151 and 1313 K were determined for the Dy2O2S and Dy2O2SO4 materials, respectively. The photoluminescence properties of the dysprosium oxysulfide were investigated, showing narrow emission bands assigned to the 4F9/2→6HJ intraconfigurational transitions of the Dy3+ ion. The yellow emission color of this phosphor suggests that the Dy2O2S is a promising material for applications in LEDs.

[RE(TMA)] anhydrous complexes (RE3+: Y, Gd and Lu) present high red emission intensity with a quantum efficiency (~45%) for the [Y(TMA):Eu3+] complexes, due to the absence of non-radioactive decay pathways mediated by water molecules. The complexes were prepared in mild conditions. All the compounds are crystalline and thermostable up to 460 °C. Phosphorescence data of the complexes with Y, Gd and Lu show that the T1 state of the TMA3− anion has energy higher than the 5D0 emitting level of the Eu3+ ion, indicating that the ligand can act as an intramolecular energy sensitizer. The photoluminescence properties of the doped materials were studied based on the excitation and emission spectra and luminescence decay curves. The experimental intensity parameters (Ωλ), lifetimes (τ), radiative (Arad) and non-radiative (Anrad) decay rates were determined and discussed.

Three organic–inorganic hybrid materials based on silica gel functionalized with (3-aminopropyl)trimethoxysilane (APTS), [3-(2-aminoetilamino)-propil]-trimetoxissilano (DAPTS) and 3-[2-(2-aminoetilamino)etilamino] propiltrimetoxysilane (TAPTS) and subsequently modified with EDTA derivative were prepared by nonhomogeneous route and were then characterized. The resulting materials named SilXN-EDTA (X=1 for APTS, 2 for DAPTS and 3 for TAPTS) were used to obtain new lanthanide Ln3+-β-diketonate (Ln3+=Eu3+, Gd3+ and Tb3+) complexes covalently linked to the functionalized silica gel surfaces (named SilXN-EDTALn-dik, dik=tta, dbm, bzac and acac). The photophysical properties of the new luminescent materials were investigated and compared with those with similar system presenting water molecules coordinated to the lanthanide ions, SilXN-EDTALn-H2O. The SilXN-EDTAEu-dik and SilXN-EDTATb-dik systems displayed characteristic red and green luminescence when excited by UV radiation. Furthermore, the quantitative results showed that the emission quantum efficiency (η), experimental intensity parameters Ω2 and Ω4, and Einstein's emission coefficient (A0J) of the SilXN-EDTAEu-dik materials were largely dependent on the ligands. Based on the luminescence data, the most efficient intramolecular energy transfer processes were found to the SilXN-EDTAEu-dik (dik: tta and dbm) and SilXN-EDTATb-acac materials, which exhibited more pure emission colors. These materials are promising red and green phosphors, respectively.

The impurities and dopants' inappropriate valences may deteriorate the performance of luminescent materials, cause waste of the precious rare earth (R) material and thus incur financial losses. The usual methods to detect the valence of rare earths; XPS, Mossbauer and XANES spectroscopies, are not sensitive enough for low concentrations and the EPR methods are not very suitable for powders. In this work, the comparison between the theoretical and experimental temperature-dependent paramagnetic susceptibilities was used to obtain quantitatively the concentrations of the impurity valence in Eu 2 O 2 S and Tb 2 O 2 SO 4 , both containing nominally only R 3+ . Minute (ppm level) Eu 2+ impurities could be analyzed because of the huge difference in the paramagnetic susceptibility between Eu 2+ and Eu 3+ at low temperatures. However, temperatures below 50 K are then needed whilst the Tb IV impurity in a Tb 3+ matrix can be observed already at higher temperatures. The latter method based on comparing the slopes of the Tb 3+ /Tb IV paramagnetic susceptibility vs temperature curves for the Tb 3+ /Tb IV couple is less sensitive than for the Eu 2+ /Eu 3+ one. Finally, the host independent temperature evolution of the paramagnetic susceptibility was calculated for Gd 3+ (or Eu 2+ or Tb IV ) to yield a simple analytical expression to be used universally.

Persistent luminescence materials Lu2O3:R(3+),M (Pr,Hf(IV); Eu; or Tb,Ca(2+)) were successfully and rapidly (22 min) prepared by microwave-assisted solid-state synthesis (MASS) using a carbon microwave susceptor and H3BO3 as flux. Reaction times are reduced by up to 93% over previous synthetic methods, without special gases application and using a domestic microwave oven. All materials prepared with H3BO3 flux exhibit LuBO3 impurities that were quantified by Rietveld refinement from synchrotron radiation X-ray powder diffraction patterns. The flux does not considerably affect the crystalline structure of the C-Lu2O3, however. Scanning electron micrographs suggest low surface area when H3BO3 flux is used in the materials' synthesis, decreasing the amount of surface hydroxyl groups in Lu2O3 and improving the luminescence intensity of the phosphors. The carbon used as the susceptor generates CO gas, leading to complete reduction of Tb(IV) to Tb(3+) and partial conversion of Pr(IV) to Pr(3+) present in the Tb4O7 and Pr6O11 precursors, as indicated by X-ray absorption near-edge structure data. Persistent luminescence spectra of the materials show the red/near-IR, reddish orange, and green emission colors assigned to the 4f(n) → 4f(n) transitions characteristics of Pr(3+), Eu(3+), and Tb(3+) ions, respectively. Differences between the UV-excited and persistent luminescence spectra can be explained by the preferential persistent luminescence emission of R(3+) ion in the S6 site rather than R(3+) in the C2 site. In addition, inclusion of Hf(IV) and Ca(2+) codopants in the Lu2O3 host increases the emission intensity and duration of persistent luminescence due to generation of traps caused by charge compensation in the lattice. Photonic materials prepared by MASS with H3BO3 flux show higher persistent luminescence performance than those prepared by the ceramic method or MASS without flux. Color tuning of persistent luminescence in Lu2O3:R(3+),M provides potential applications in bioimaging as well as in solar cell sensitizers.

In this work, the coordination compounds presenting the formulas [Eu(acac)(NO3)2 (phen)2]⋅H2O (Eu1) and [Eu(bzac)(NO3)2(phen)2]⋅H2O (Eu2), acac: acetylacetonate, bzac: benzoylacetonate and, phen: 1,10-phenantroline, were successfully synthesized and some spectroscopic properties were investigated by theoretical and experimental methods. These compounds were characterized via elemental analysis, FTIR spectroscopy and thermogravimetric analysis (TGA). The X-ray diffraction data revealed that the compound Eu1 crystallizes in the monoclinic space group P2/n. Spectroscopic data showed that ligand-to-metal charge transfer states (LMCT) in the [Eu(β-dik)(NO3)2(phen)2]⋅H2O complexes (β-dik: acac or bzac) are redshift as compared with [Eu(β-dik)3(phen)] complexes. These data showed that LMCT states play the most important role on the luminescence quenching in the complexes Eu1 and Eu2, which only exhibit high luminescence intensities at low temperatures. Furthermore, the role of changes in the chemical environment on the intensity parameters Ωλ (λ = 2 and 4) have been investigated from the theoretical point of view for the complexes Eu1 to Eu2, and from these to tris β–dik complexes. Interestingly, the theoretical intensity parameters ratio Ω2/Ω4 calculated are in a good agreement with those experimental ones.

The coordination network consisting of trivalent bismuth ions and pyromellitic acid (H4Pyr), [Bi(HPyr)], was successfully applied as a host matrix for in situ incorporation of trivalent rare earth (RE3+) ions Sm3+, Eu3+, Tb3+ and Dy3+. High-throughput methods for hydrothermal synthesis allowed us to prepare and study the phase purity and crystallinity of the sample series, accelerating and facilitating the comparison between the synthesis parameters. Infrared absorption spectroscopy, elemental and thermogravimetric analysis, scanning electron microscopy and energy-dispersive X-ray spectroscopy, as well as powder X-ray diffraction and refinement of the unit cell parameters of the compounds, indicated that doping did not affect the structure, crystallinity, morphology and thermal stability of the matrix. The study of the spectroscopic luminescence properties of the nondoped and doped [Bi(HPyr)] allowed investigation of the sensitization processes of dopant RE3+ ions. The characteristic spectroscopic properties of the Eu3+ ion were used to study the incorporation site and coordination environment of the dopant by calculation of the experimental intensity parameters Ωλ (λ: 2 and 4) and intrinsic quantum yield of the Eu3+ single-doped [Bi(HPyr)]. Straightforward emission color tuning by changing the relative concentrations of the dopant ions is possible and has been studied for the four systems double-doped with Tb3+:Eu3+, Tb3+:Sm3+, Dy3+:Eu3+ and Dy3+:Sm3+ ions. The Dy-containing systems show different shades of white emission and a wide range of correlated color temperatures (CCT), ranging from 2500 to 7500 K, hence being a promising candidate for the development of single-phase white light emitting devices.

Y2O2SO4:Eu3+ with monoclinic crystalline structure was synthesized in air by low temperature thermolysis (500 °C, 1 h) of RE3+-STMA precursors (RE: Rare Earth, STMA: 5-sulfoisophthalate). The annealing of the samples for 1 h at temperatures ranging from 500 to 1000 °C promotes a nanometric phase (18–89 nm) with increased crystallinity for higher temperatures. At the limit temperature of 1100 °C, the complete removal of Sulfur atoms leads to the formation of highly luminescent Y2O3:Eu3+ nanocrystals. Evaluation of the luminescent properties of the particles produced at different calcination temperature showed high emission quantum efficiencies (η = 44–70%).