Hypersensitive 5D0 Research Articles

Site selective spectroscopy in BaYF5:RE3+ (RE = Eu, Sm) nano-glass–ceramics

Trivalent rare-earth (RE=Eu, Sm) doped transparent nano-glass–ceramics comprising BaYF5 nanocrystals were successfully obtained by appropriate heat-treatment of the corresponding precursor sol–gel glasses. Their structural and spectroscopic properties were investigated and compared with those for Eu3+-doped-BaYF5 nanocrystals prepared by a solvothermal method. X-ray Diffraction, Transmission Electron Microscopy and Energy Dispersive X-ray Spectroscopy measurements confirmed the distribution of BaYF5 nanocrystals in the glass matrix, presenting a cubic phase structure with space group Fm-3m. In order to achieve a further structural characterization, the luminescence properties of the Eu3+ and Sm3+ dopants were also used as sensitive probes. The reduction in the emission intensities of hypersensitive transitions 5D0→7F2 and 4G5/2→6H9/2 for Eu3+ and Sm3+ ions respectively, along with time-resolved measurements, confirm the distribution of a significant fraction of RE ions into the fluoride nanocrystal environment. These results suggest that BaYF5 nano-glass–ceramics doped with Eu3+ or Sm3+ can be considered as potential red-emitting phosphors for the development of white LEDs under near UV excitation.

Photoluminescence and structural properties of Eu3+ doped SrZnV2O7 nanocrystals

Novel SrZn1−xEuxV2O7 nanoparticles were synthesized employing urea assisted solution combustion process. The Rietveld refinement technique was used to study the effect of Eu3+ doping on the crystal structure of the host lattice. It was found to crystallize in monoclinic lattice with the P121/c1 (14) space group. The photoluminescent spectral analysis showed that upon excitation in the near UV region, these nanophosphors can emit very intense red luminescence (616nm) corresponding to the hypersensitive 5D0→7F2 transition of Eu3+ ions. X-ray diffraction studies revealed the low symmetrical co-ordinative environment of the activator ion (trigonal bipyramidal) with no inversion center in the SrZnV2O7 host lattice. The optimum concentration of Eu3+ ion in SrZnV2O7 for better luminescence was found to be 4mol% The critical distance for energy transfer (24.1602Å) imparted the initial idea of intensity variation as a function of dopant concentration. Dipole–dipole (d–d) interactions were successfully accounted for the concentration quenching arising from the over-doping of the activator ions. These near UV light absorbers (395nm) can be thrivingly used in white LEDs using lnGaN chip system, plasma display panels (PDPs) and solid state laser.

La(OH)3:Eu3+and La2O3:Eu3+nanorod bundles: growth mechanism and luminescence properties

Oriented attachment assisted self-assembled three-dimensional (3D) flower-like La(OH)3:Eu3+ nanorod bundles were successfully synthesized by a facile wet-chemical method. Hexamethylenetetramine played an important role in the formation of the hexagonal phase of La(OH)3:Eu3+ with respect to the reaction time and its concentration. No other surfactants or capping agents were used. The calcination temperature did not show any influence on the morphological texture, and the La2O3:Eu3+ phase was obtained by a subsequent annealing process. The phase formation and morphological properties were confirmed by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The photoluminescence properties were studied for both the synthesized La(OH)3:Eu3+ and La2O3:Eu3+ samples, and also compared with that of the solid-state reaction based La2O3:Eu3+ phosphor. The 3D flower-like La2O3:Eu3+ nanorod bundles showed an intense red emission due to the hypersensitive 5D0 → 7F2 transition with good asymmetric ratio and chromaticity coordinates. Likewise, a systematic study of the cathodoluminescence (CL) properties was carried out in detail. Furthermore, to estimate the CL potentiality, the La2O3:Eu3+ phosphor was compared with a commercially available Y2O3:Eu3+ red phosphor.

Crystal structure and photoluminescent properties of BaZn1−xEuxV2O7 nanoparticles

The structure of novel BaZn1−xEuxV2O7 nanoparticles (synthesised employing solution combustion process) was refined and determined from X-ray diffraction (XRD) profiles by the Rietveld refinement method. It was found to crystallize in orthorhombic lattice with the Pnma space group. Further structural informations and particle morphology were investigated using FT-IR spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photoluminescence spectral analysis showed that these nanophosphor can be effectively excited by near-UV light (305 nm, 395 nm), emitting intense red luminescence (620 nm) corresponding to the hypersensitive 5D0→7F2 transition of Eu3+ ion, located at low-symmetry site with no inversion center in BaZnV2O7 crystal lattice. The dependence of luminescence intensity and chromaticity index on Zn2+ substitution by Eu3+ ions in BaZnV2O7 was also investigated which unveil 5 mol% as the optimum concentration. These nanophosphors are potential candidate for white LEDs using near ultra-violet (NUV) LED chip excitation.

Magnetofluorescent probe of superparamagnetic iron oxide nanoparticles modified with poly(TMSMA-r-PEGMA-r-Eu(NTA)3(MMA)(TOPO)3).

In this study, hybrid magnetofluorescent structures composed of organic moiety of poly(TMSMA-r-PEGMA) for biomolecules-resistant surfaces and methyl methacrylate for conjugation of europium complex inorganic moiety of magnetic nanoparticles are reported. Lanthanide complex of europium ion with 4,4,4-Trifluoro-1-(2-naphthyl)-1,3-butanedione (NTA) and trioctylphosphine oxide (TOPO)[Eu(NTA)3(TOPO)3] were incorporated into poly(TMSMA-r-PEGMA-r-MMA) matrix. Afterward, superparamagnetic iron oxide nanoparticles (SPIONs) were coated with as prepared polymeric europium complex (PEC) to construct hierarchical structure of magnetofluorescent probe. The PL spectra of the PEC@SPIONs excited by UV light showed characteristic emission behavior with a hypersensitive transition 5D0 --> 7F2 at 621 nm. About a 20% quenching in the intensity of the emission peak at 621 nm was found after the addition of SPIONs. Interestingly, when the concentration of PEC against SPIONs is increased, the hypersensitive transition 5D0 --> 7F2 at 621 nm is linearly increased, while 5D1 --> 7F6 at 700 nm is linearly decreased. The cytotoxic effect of PEC@SPIONs was evaluated with U373MG cell by the MTT assay of PEC@SPIONs in cell proliferation. The cell viability in the range of 10-200 ug/ml was more than 80%. No significant difference in cell proliferation until the concentration of 300 ug/ml (77.61 ± 3.33%). The cellular uptake of PEC@SPIONs evaluated by confocal microscopy showed that the magnetofluorescent nanoparticles were internalized extensively in the cytoplasmic region.

Combustion Synthesis and Optical Properties of Eu3+-Doped BaGd2ZnO5 f–f Transition Nanophosphor for White LED

An Eu3+-doped BaGd2(1−x)ZnO5 nanophosphor has been synthesized by means of a single-step, urea-assisted, solution-combustion process. The structural, morphological, and optical properties of the nanophosphor were studied by x-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy. The XRD results showed that the pure orthorhombic BaGd2ZnO5 structure with space group Pbnm was obtained at 900°C. The intense red luminescence at 628 nm on near-UV (396 nm) excitation is because of the hypersensitive 5D0 → 7F2 transition of luminescent activator Eu3+ ions, located at a site with no inversion symmetry in the BaGd2ZnO5 crystal lattice. The optimum doping concentration and decay time of Eu3+-doped BaGd2(1−x)ZnO5 nanophosphor were also determined. The emission could be effectively tuned from blue to the white and red regions by varying the concentration of europium ions. Decay curve analysis revealed that cross-relaxation is primarily responsible for the concentration quenching. High luminescent intensity, low-cost, easy synthesis, uniform shape, and controlled color tunability suggest use of BaGd2ZnO5:Eu3+ as an efficient red-emitting nanophosphor for near-UV-based LED solid-state lighting applications.

Low-temperature synthesis, phonon and luminescence properties of Eu doped Y3Al5O12 (YAG) nanopowders

This contribution presents two simple and cost-effective routes for the low-temperature and large-scale production of pure and Eu-doped Y3Al5O12 (yttrium aluminum garnet YAG) nanopowders. The proposed methodologies combine a mechanically assisted metathesis reaction or coprecipitation from solution followed by crystallization of the obtained precursors from molten sodium nitrate/nitrite. Both procedures allow obtaining pure and/or doped YAG nanopowders at remarkably low temperatures, i.e. already at 350 °C although firing at 500 °C is needed in order to get single phase and fully crystalline materials. As-obtained samples were characterized by XRD, TEM, Raman, IR and luminescence methods. These methods showed that the mean crystallite size is near 23–31 and 51 nm, when crystallization is performed from the amorphous precursor obtained by a mechanically assisted metathesis reaction and coprecipitation, respectively. Raman and IR spectra indicated better crystallinity of the powders prepared at 500 °C. The emission study showed that the intensity ratio between hypersensitive 5D0 → 7F2 and magnetic-dipole 5D0 → 7F1 transitions of Eu3+ is significantly larger than expected for well-crystallized YAG. Origin of this behavior is discussed.

Influence of TTAB on morphology and photoluminescence of GdVO4:Eu3 + powders in a wide pH range

We demonstrate that the critical issue of controllable growth of GdVO4:Eu3+ crystal particles is solved by “tetradecyltrimethyl ammonium bromide (TTAB)” in a variable pH range. The microstructure, morphology, and luminescence property of the phosphors were investigated by X-ray powder diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The results suggested that the surfactant TTAB was a key factor for determining the morphology of final GdVO4:Eu3+ crystals. The influence of pH on the nucleation rate was studied as well. The PL results indicated that the PL property of the GdVO4:Eu3+ phosphors was crucially impacted by the micro-structure and morphology. All the phosphors mainly showed strong red emissions at 615 and 618nm originating from the hypersensitive transition 5D0→7F2 of Eu3+ ions. The nano-sized phosphors showed prominent PL properties due to the grain size effect. The crystalline state and the microstructure of the products also affected the PL performance.

Luminescence and structural properties of Eu3+ doped BaY2ZnO5 for LED solid-state lighting application

Eu3+ doped BaY2(1−x)ZnO5 phosphor was successfully synthesized by a single step solution combustion process. The crystal structure and particle morphology were investigated by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy. The XRD results suggest that BaY2ZnO5 crystallizes in a single phased orthorhombic structure with space group Pbnm at 1,100 °C. The phosphor can be effectively excited by near-UV light, emitting intense red luminescence (628 nm) corresponding to the hypersensitive 5D0 → 7F2 transition of Eu3+ ions, located at low-symmetry site with no inversion center in BaY2ZnO5 crystal lattice. Fluorescence decay analysis was carried out to understand the energy transfer mechanism and quenching behavior of luminescence of Eu3+ ions in the BaY2ZnO5 phosphor. The BaY2ZnO5: Eu3+ emission (λex = 395 nm) could be tuned from blue to white and red light by varying the Eu3+ ions concentration, making this phosphor as a promising candidate for LEDs application.

Effects of host composition, Al3+ as a sensitizer and SiO2 surface coating on luminescence intensity, color purity of MVO4: Al3+, Eu3+ @ SiO2 (M = Gd, Y and Gd/Y) red phosphors

MVO4: Al3+, Eu3+@ SiO2 powder phosphors have been synthesized by a modified colloidal precipitation technique followed by calcination. Luminescence optimization was fine tuned mainly in three stages, by investigating the effects of: (i) host composition (Gd, Y and Gd/Y), (ii) co-dopant Al3+ as a sensitizer and finally (iii) with SiO2 coating as a surface protecting layer. XRD data revealed that the produced phosphors were well crystalline and possess body centered tetragonal phase. SEM micrographs illustrate that the synthesized phosphor particles are loosely bound with tetragonal like morphology and consists 1–5 μm dia grain size. Silica coating on phosphor particles were characterized by SEM/EDAX, TEM, FT-IR and PL measurements. An intense charge transfer excitation band owing to VO43− has dominated the f–f transitions of Eu3+ ions. The emission intensities of the hypersensitive 5D0 → 7F2 transitions are stronger than the magnetic dipole 5D0 → 7F1, indicates lowering of inversion symmetry in the vicinity of Eu3+, ions. Red color richness owing to the efficient energy transfer from Al3+ to Eu3+ with Y0.94VO4: Al3+0.01, Eu3+0.05 phosphor were enhanced significantly by 3 times stronger than the phosphor Y0.95VO4: Eu3+0.05, which was further increased 1.2 times with SiO2 protecting layer.

Pressure-induced phase transitions in sodium europium carbonate (Na3Eu(CO3)3) and europium-doped yttrium sesquioxide (Y2O3:Eu3+) by time-resolved laser fluorescence spectroscopy

Time-resolved laser fluorescence spectroscopy has been used to investigate pressure-induced phase transitions in Y2O3:Eu3+ and Na3Eu(CO3)3. Na3Eu(CO3)3 shows a reversible structural phase transformation at 10.5 GPa that can be monitored by fluorescence spectroscopy, fluorescence lifetime measurements and X-ray diffraction. The bulk modulus of Na3Eu(CO3)3 was determined to be B=55(2) GPa from synchrotron X-ray diffraction data. The pressure-induced phase transformations of Y2O3:Eu3+ were characterised by fluorescence lifetime measurements of the hypersensitive 5D0→7F2 transition, which allowed us to monitor the pressure-induced increase in the coordination number.

Structure evolution and tunable luminescence of (Sr0.98−mBamEu0.02)2Ca(Mo1−nWn)O6 phosphor with ultraviolet excitation for white LEDs

Double perovskite (Sr0.98−mBamEu0.02)2Ca(Mo1−nWn)O6 phosphors were successfully synthesized by an improved citrate–EDTA complexing method. The structure evolution and the resulting luminescence variation were systematically investigated by X-ray diffraction with Rietveld structure refinement, Fourier transform infrared spectra, Raman spectra, diffuse reflection spectra and photoluminescence spectra. The increased crystal symmetry and increased lattice parameters were observed from (Sr0.98−mBamEu0.02)2CaMoO6 phosphors. These series of phosphors could be effectively excited by near ultraviolet light and emitted a dominant 594nm (5D0–7F1). The hypersensitive 5D0–7F2 transition (615nm) varied with the changed structure symmetry. The CIE chromaticity coordinates were tuned from (0.642, 0.348) to (0.601, 0.389). The luminescence intensity of W6+ substituted powders was greatly enhanced by the blue shift of charge transition band of (Mo/W)O6 with stable emission color. The composition-optimized Sr2Ca(Mo0.5W0.5)O6:Eu phosphor had the highest luminescence intensity and quantum yield comparing to the commercial red phosphors.

Molecular interactions between serum albumin proteins and Keggin type polyoxometalates studied using luminescence spectroscopy

The interaction between the plenary Keggin H3PW12O40, lacunary Keggin K7PW11O39 and the Eu(III)-substituted Keggin K4EuPW11O39 (Eu-Keggin) type polyoxometalates (POMs), and the proteins human and bovine serum albumin (HSA and BSA) was studied using steady state and time-resolved Eu(III) luminescence and tryptophan (Trp) fluorescence spectroscopy. The excitation spectrum of the Eu-Keggin POM is dominated by a ligand-to-metal charge transfer band at 291 nm. In the absence of proteins, the number of water molecules coordinated in the first coordination sphere of the Eu(III) center of Eu-Keggin was determined to be 4, indicating that Eu(III) occurs as a 1 : 1 isomer in solution. In the presence of HSA or BSA, the number of coordinated water molecules decreased to 0 and 1, respectively, suggesting interaction between the Eu-Keggin POM and the protein surface. As a result of this interaction, a five-fold increase of the hypersensitive (5)D0 → (7)F2 transition in the luminescence intensity was observed for the Eu-Keggin-HSA complex. The association constants were calculated to be 1.5 × 10(2) M(-1) and 2.0 × 10(3) M(-1) for the Eu-Keggin-HSA and Eu-Keggin-BSA complexes, respectively. Tryptophan fluorescence quenching studies were performed and the quenching constants were calculated using a Stern-Volmer analysis. The obtained values of the quenching constants were 6.1 × 10(4) M(-1) and 2.0 × 10(6) M(-1) for the Eu-Keggin-HSA and Eu-Keggin-BSA complexes, respectively. The surface map of both proteins shows that the cavity containing the tryptophan has a positive surface potential, providing a specific binding site at the surface of albumin proteins for the negatively charged POM.

Synthesis, structural and optical properties of Eu3+–doped Ca2V2O7 nanophosphors

Europium doped calcium pyrovanadate nanoparticles Ca2V2O7:Eu3+, having a size of 57–63 nm, were synthesized using combustion process. Structure, morphological and optical properties of nanophosphors have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), fluorescence spectrometry (PL) and Fourier transform infra-red (FT-IR) spectroscopy. X-ray studies shows that a pure triclinic Ca2V2O7 phase was obtained at 900 °C temperature. The red emission observed at 620 nm upon excitation at 305 nm is due to hypersensitive transition 5D0 → 7F2 of luminescent activator Eu3+ location at a site with no inversion symmetry in Ca2V2O7 crystal lattice. High luminescent intensity and easy synthesis technique make this red phosphor a promising candidate for application as luminescent materials.

Strongly luminescent, highly ionic europium in a lanthanum diphenylphosphinate matrix

A series of insoluble, chemically inert and thermally stable compounds La1−xEux(DPP)3 (x=0.50, 0.20, 0.10, and 0.050; DPP=diphenylphosphinate) was synthesized and characterized by elemental and thermogravimetric analysis, FT Infrared spectroscopy and X-ray powder diffraction. Luminescence spectroscopy at both 77 and 298K showed changes in the intensity of the hypersensitive transition 5D0→7F2 of Eu3+ which are dependent of the excitation wavelength, suggesting that the europium occupies two different sites in the compounds. The large quantum efficiency and quantum yield, as well as the long radiative lifetime of the 5D0 Eu3+ level of the series of compounds, which are desirable qualities for light-conversion molecular devices, are discussed in terms of the interactions and the energy transfer process between the ligands and the metal ion.

Photoluminescence investigations of Li2SiO3:Ln (Ln=Er3+, Eu3+, Dy3+, Sm3+) phosphors

In this study, we report a comprehensive structural and photoluminescence (PL) study on lithium metasilicate (Li2SiO3) phosphor ceramics doped with four rare earth (RE) ions. X-ray diffraction (XRD) patterns show a dominant phase, characteristic of the orthorhombic structure Li2SiO3 compound and the presence of dopants has no effect on the basic crystal structure of the material. The first excited state Er3+ luminescence at 1.54μm arises from a sharp atomic-like radiative transition between the 4I13/2 state and the 4I15/2 state (ground level) under a 532nm line of an Ar ion laser excitation. Sm doped samples showed Sm3+ emission characteristics corresponding to the some 4G5/2→6Hj (j=5/2,9/2,11/2) transitions indicating a strong crystal-field effect. PL spectra of Eu doped material exhibited peaks corresponding to the 5D0→7Fj (j=0,1,2,3 and 4) transitions under 405nm excitation. The dominant red color emission at 612nm from the hypersensitive (5D0→7F2) transition of Eu3+ indicates the inversion antisymmetry crystal field around Eu3+ ion, which is favorable to improve the red color purity. Dy doped samples showed the Dy3+ emission characteristic due to the 4F9/2→6H13/2 transition. Their relative intensity ratios also suggested the presence of a symmetric environment around the metal ion. We suggest that lithium metasilicate has enough potential candidates to be a phosphor material.

Luminescent nine-coordinate lanthanide complexes derived from fluorinated β-diketone and 2,4,6-tris(2-pyridyl)-1,3,5-triazine

The synthesis, photoluminescence, 4f–4f absorptions, and NMR studies of nine-coordinate lanthanide(III) complexes, [Ln(tfaa)3(tptz)] (Ln = La, Nd, Sm, and Eu; tfaa is the anion of 1,1,1-trifluoro-2,4-pantanedione; and tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine), are reported. These complexes are synthesized in a single pot by in situ method and thoroughly characterized. The β-diketone and tptz chemical shifts, in the cases of paramagnetic complexes, are in the opposite directions. The lanthanide-induced shifts are dipolar in nature. The luminescence and 4f–4f absorptions are analyzed and discussed. The samarium and europium complexes emit strong pink and red luminescences due to 4G5/2 → 6Hj (j = 5/2, 7/2, 9/2) and 5D0 → 7Fj (j = 0–4) transitions, respectively. The 4G5/2→6H7/2 (607 nm) emission transition of Sm(III) has no Stark components and indicates a higher local symmetry around Sm(III). The very strong hypersensitive 5D0 → 7F2 transition of Eu reflects a highly polarizable chemical environment around Eu(III). The absorption spectra of the neodymium complex are investigated and analyzed.

Synthesis of a functionalized europium complex and deposition of luminescent Langmuir–Blodgett (LB) films

The synthesis, characterization and formation of Langmuir–Blodgett (LB) films for the luminescent [(C12H25)2(CH3)2N][Eu(tta)4] complex, where [(C12H25)2(CH3)2]N+ is didodecyldimethylammonium and the tta ligand is thenoyltrifluoroacetone, are reported. The coordination of tta ligands to the Eu3+ ion was confirmed by FTIR spectroscopy and the emission spectrum comprised bands corresponding to 5D0 → 7F0–4 transitions. The lifetime (τ) from the emission state (5D0) was 0.41 ms, measured by monitoring the hypersensitive 5D0 → 7F2 transition, with the curve being fitted with a first-order exponential function. The surface pressure–area isotherm indicated that the anionic complex may form condensed structures at the air–water interface due to the amphiphilic properties of the counter ion and the β-diketone ligand. Y-type LB films of [(C12H25)2(CH3)2N][Eu(tta)4] were deposited on quartz substrates, with preserved luminescence and a band assigned to the 5D0 → 7F2 transition. The molecular arrangement at the air/water interface and the preserved luminescence in LB films are consistent with theoretical predictions using a semi-empirical Sparkle/AM1 calculation method for the molecule in vacuum. These tools were used for the first time to predict the behavior of organized films.

Synthesis and optical characterization of strong red light emitting KLaF4:Eu3+ nanophosphors

Monophasic KLaF4 possessing cubic symmetry with varied Eu3+ concentrations were synthesized by wet-chemical reaction. The obtained nanophosphor exhibits nanocrystals of 5nm size and the dopant Eu3+ ions were successfully incorporated into the sites of La3+ ions of the host lattice. The dominant red color emission at 612nm from the hypersensitive (5D0→7F2) transition of Eu3+ indicates the inversion antisymmetry crystal field around Eu3+ ion, which is favorable to improve the red color purity. Furthermore, the emission life times are high enough and our results broadly suggest the potential application for white LEDs, mercury-free lamps and display panels.

Crystal field effects on the photoluminescence properties of Y1−x La x VO4:Eu3+ phosphors

Y1−xLaxVO4:Eu3+ phosphors were synthesized using a solid-state reaction. The microstructure and surface morphology of the Y1−xLaxVO4:Eu3+ phosphors were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. PL measurements of these phosphors revealed the characteristic Eu3+ emissions due to 5D0→7F1 and 5D0→7F2 transitions. The Y1−xLaxVO4:Eu3+ phosphors showed strong red emission at 619 nm, which radiated from the hypersensitive transition 5D0–7F2 of Eu3+ ions. In particular, the incorporation of La into the YVO4 lattice could induce a remarkable increase in PL. The highest emission intensity was observed in Y0.2La0.8VO4:Eu3+, whose brightness was increased by more than 100 fold compared to that of the LaVO4:Eu3+ phosphors. The Y1−xLaxVO4:Eu3+ phosphors with highly enhanced luminescence are expected to have applications in display devices.