The determination of the Mg2+.ATP dissociation constant by competition with Eu3+ ion using laser-induced Eu3+ ion luminescence spectroscopy

A direct spectroscopic method for the determination of the submicromolar dissociation constant of Eu3+. ATP using laser-induced Eu3+ ion luminescence spectroscopy is described. The dissociation constant of Mg2+.ATP is then determined by the competition of Mg2+ with Eu3+ for the binding of ATP. The experiments were performed in 2H2O to mitigate the significant quenching of the Eu3+ luminescence that occurs in 1H2O. Values for the effective dissociation constants of the 1:1 ATP metal ion complexes of 1.2 +/- 0.3 X 10(-7) and 2.7 +/- 0.7 X 10(-4) M are obtained for Eu3+ and Mg2+, respectively, at p2H 5.8.     

Absorption and luminescence spectroscopy of Eu3+ in lead silicate glasses

The absorption and luminiscence spectra of a lead silicate glass containing Eu³⁺ as impurity have been measured. The doping ion was found to occupy two classes of non-centrosymmetric sites. The intensities of the 4f⁶→4f⁶ transitions are perturbed by the interaction with low-lying charge-transfer states. The quantum yield of the luminescence from the ⁵D₀ level of Eu³⁺ is usually low, probably because of the presence of a strong ion-phonon coupling.     

Binding of Eu3+ to cardiac sarcoplasmic reticulum (Ca2+ + Mg2+)-ATPase-laser excited Eu3+ spectroscopic studies.

The binding of Eu3+ with Ca2+-stimulated, Mg2+-dependent adenosine triphosphatase ([Ca2+ + Mg2+]-ATPase) of cardiac sarcoplasmic reticulum (SR) has been investigated using direct laser excited Eu3+ luminescence. Eu3+ is found to inhibit both Ca2+-dependent ATPase activity and Ca2+-uptake in a parallel manner. This is attributed to the binding of Eu3+ to the high affinity Ca2+-binding sites. The Ki for Ca2+-dependent ATPase is approximately 50 nM. The 7F0----5D0 excitation spectrum of Eu3+ in cardiac SR shows a peak at 579.3 nm, as compared to 578.8 nm in potassium-morpholino propane sulfonic acid (K-MOPS) pH 6.8. Upon binding with cardiac SR, Eu3+ shows an increase in fluorescence intensity as well as in lifetime values. The fluorescence decay of bound Eu3+ exhibits a double-exponential curve. The apparent number of water molecules in the first coordination sphere of Eu3+ in SR is 2.8 for the short component and 1.0 for the long component. In the presence of ATP, a further increase in fluorescence lifetimes is observed, and the number of water molecules in the first coordination sphere of Eu3+ is reduced further to 1.3 and 0.5. The double exponential nature of the decay curve and the different number of water molecules coordinated to Eu3+ for both decay components suggest that Eu3+ binds to two sites and that these are heterogeneous. The reduction in the number of H2O ligands in the presence of ATP shows a change in the molecular environment of the Eu3+-binding sites upon phosphoenzyme formation, with a movement of Eu3+ to an occluded site on the enzyme.     

Enhancing the luminescence of Eu3+/Eu2+ ion‐doped hydroxyapatite by fluoridation and thermal annealing

This paper reports a novel way for the synthesis of a europium (Eu)‐doped fluor‐hydroxyapatite (FHA) nanostructure to control the luminescence of hydroxyapatite nanophosphor, particularly, by applying optimum fluorine concentrations, annealed temperatures and pH value. The Eu‐doped FHA was made using the co‐precipitation method followed by thermal annealing in air and reducing in a H₂ atmosphere to control the visible light emission center of the nanophosphors. The intensities of the OH^? group decreased with the increasing fluorine concentrations. For the specimens annealed in air, the light emission center of the nanophosphor was 615 nm, which was emission from the Eu³⁺ ion. However, when they were annealed in reduced gas (Ar + 5% H₂), a 448 nm light emission center from the Eu²⁺ ion of FHA was observed. The presence of fluorine in Eu‐doped FHA resulted in a significant enhancement of nanophosphor luminescence, which has potential application in light emission and nanomedicine.     

Lanthanide-binding tags with unnatural amino acids: sensitizing Tb3+ and Eu3+ luminescence at longer wavelengths

Lanthanide-binding tags (LBTs) are small, genetically encoded, versatile protein fusion partners that selectively bind lanthanide ions with high affinity. The LBT motif features a strategically positioned tryptophan residue that sensitizes Tb3+ luminescence upon excitation at 280 nm. Herein, we describe the preparation of new LBT peptides that incorporate unnatural amino acids in place of tryptophan, and which sensitize both Tb3+ and Eu3+ luminescence at lower energies. We also report the semisynthesis of proteins tagged with these new LBTs using native chemical ligation. This expands the scope of LBTs and will enable their wider use in luminescence applications.     

Synthesis and luminescence study of Eu3+‐doped SrYAl3O7 phosphor

Rare‐earth ions play an important role in eco‐friendly solid‐state lighting for the lighting industry. In the present study we were interested in Eu³⁺ ion‐doped inorganic phosphors for near ultraviolet (UV) excited light‐emitting diode (LED) applications. Eu³⁺ ion‐activated SrYAl₃O₇ phosphors were prepared using a solution combustion route at 550°C. Photoluminescence characterization of SrYAl₃O₇:Eu³⁺ phosphors showed a 612 nm emission peak in the red region of the spectrum due to the ⁵D₀→⁷F₂ transition of Eu³⁺ ions under excitation at 395 nm in the near‐UV region and at the 466 nm blue excitation wavelength. These red and blue emissions are supported for white light generation for LED lighting. Structure, bonding between each element of the sample and morphology of the sample were analysed using X‐ray diffraction (XRD) and scanning electron microscopy (SEM), which showed that the samples were crystallized in a well known structure. The phosphor was irradiated with a ⁶⁰Co‐γ (gamma) source at a dose rate of 7.2 kGy/h. Thermoluminescence (TL) studies of these Eu³⁺‐doped SrYAl₃O₇ phosphors were performed using a Nucleonix TL 1009I TL reader. Trapping parameters of this phosphor such as activation energy (E), order of kinetics (b) and frequency factor (s) were calculated using Chen's peak shape method, the initial rise method and Ilich's method.     

Catalytic Ca2+-binding site of pancreatic phospholipase A2: laser-induced Eu3+ luminescence study

7F0----5D0 excitation spectroscopy of Eu3+ has been used to study the catalytic Ca2+-binding site of pancreatic phospholipases A2. Eu3+ binds competitively with Ca2+ to the enzyme with retention of about 5% of the activity found with Ca2+. The dissociation constants for the Eu3+-enzyme complexes of bovine phospholipase A2 and porcine isophospholipase A2 are 0.22 mM and 0.16 mM, respectively. Results obtained with the porcine phospholipase A2 at neutral pH indicate aggregation of this enzyme at protein concentrations above 0.18 mM. The Eu3+ bound at the catalytic site of pancreatic phospholipase A2 is coordinated to four or five water molecules, which, in conjunction with binding constant data, suggests the involvement of two or three protein ligands. Addition of a monomeric substrate analogue to the enzyme-Eu3+ complex results in the loss of an additional water molecule from the first coordination sphere of the bound Eu3+. This result suggests an interaction between the negative charge of the polar head group of the substrate analogue and the Eu3+. Binding of the enzyme-Eu3+ complex to micelles results in a nearly complete dehydration of the Eu3+ bound to the catalytic center. In the phospholipase A2-Eu3+-micelle complex, only one H2O molecule is coordinated to Eu3+. This dehydration at the active site of phospholipase A2 in the protein-lipid complex can be an important reason for the enhanced activity of this enzyme at lipid-water interfaces.     

Modification of luminescence spectra of CaF2: Eu2+

CaF₂:Eu²⁺ is a well known phosphor having efficient excitation in the near ultraviolet (NUV) range. Phosphors with NUV excitation are required in newly emerging applications such as photoluminescence liquid crystal displays (PLLCD), solid‐state lighting (SSL), and down‐conversion for solar cells. However, emission of CaF₂:Eu²⁺ is around 424 nm. Eye sensitivity drops considerably at these wavelengths. It is thus not useful for display applications for which emission in one of the primary colours (blue – 450 nm, green – 540 nm or red – 610 nm) is required. Efforts were made to modify the Photoluminescence (PL) spectra of CaF₂:Eu²⁺ to meet these requirements using co‐dopants. A Ca_0.49Sr_0.50Eu_0.01F₂ phosphor showing better colour coordinates and having an emission maximum around 440 nm was discovered during these studies. Copyright © 2015 John Wiley & Sons, Ltd.     

Combustion synthesis and luminescence properties of SrAl2O4:Eu2+, Dy3+, Tb3+ phosphor.

Eu(2+), Dy(3+) and Tb(3+) co-doped strontium aluminate phosphor with high brightness and long afterglow was synthesized by a combustion method, using urea as a reducer. The properties of SrAl(2)O(4):Eu(2+),Dy(3+),Tb(3+) phosphor with a series of initiating combustion temperatures, urea concentrations and boric acid molar fractions were investigated. The sample at initiating combustion temperature of 600 degrees C exhibited an intense emission peak at 513 nm, in which the phosphor existed as a single-phase monoclinic structure. The experimental results showed that the optimum ratio of urea is 2.0 times higher than theoretical quantities and that the suitable molar fraction of H(3)BO(3) is 0.08. The average particle size of the phosphor was 50-80 nm and its luminescence properties were studied systematically. Compared with SrAl(2)O(4):Eu(2+),Dy(3+) phosphor, the initial luminescence brightness improved from 2.50 candela (cd)/m(2) to 3.55 cd/m(2) and the long afterglow time was prolonged from 1290 s to 2743 s.     

The binding site of the strongly bound Eu3+ in Eu(3+)-regenerated bacteriorhodopsin

A Scatchard plot for the strongly bound Eu3+ to deionized bacteriorhodopsin (bR) was made using a method based on measuring the concentration of unbound Eu3+ from its fluorescence intensity. The results suggest that the first mole of Eu3+ added to a mole of bR is strongly bound by displacing 2-3 protons. In order to reconcile this result with the previous time-resolved fluorescence studies on Eu(3+)-regenerated bR, which showed the presence of 3 sites of comparable binding constants, one is forced to conclude that the emission from the strongly bound Eu3+ is completely quenched, e.g. by energy transfer to the retinal. For this to take place, the Eu3+ must be within a few A from the retinal, i.e. within the retinal pocket (the active site). The possible importance of this conclusion to the deprotonation mechanism of the protonated Schiff base, the switch of the proton pump in bR, is discussed.     

Eu2+ luminescence in SrCaP2O7 pyrophosphate phosphor

A series of Eu²⁺ activated SrCaP₂O₇ pyrophosphate phosphors were synthesized by the modified solid‐state reaction method. The X‐ray diffraction (XRD) and photoluminescence (PL) properties of these phosphors were investigated at room temperature. The excitation spectra indicate that these phosphors can be effectively excited by Hg‐free excitation. The emission spectra exhibit strong blue performance, which is due to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The Fourier transform infrared spectrum at room temperature was investigated and surface morphology has been studied by scanning electron microscope. The prepared phosphor exhibited intense blue emission at the 427 nm owing to Eu²⁺ ion by Hg‐free excitation at 330 nm, that is, solid‐state lighting excitation. Hence, the availability of such a phosphor will significantly help in the growth of blue‐emitting solid‐state lighting applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Optically stimulated luminescence in LiCaAlF6:Eu2+ phosphor

Results on optically stimulated luminescence (OSL) in LiCaAlF₆:Eu²⁺ are reported. Continuous wave OSL signal as recorded using blue (470 nm) stimulation was found to be ~31% that of standard phosphor lithium magnesium phosphate. The rate of OSL depletion for standard phosphor lithium magnesium phosphate is only three times less as compared with that of LiCaAlF₆:Eu²⁺. Strong photoluminescence (PL) in the near ultraviolet region is observed for LiCaAlF₆:Eu²⁺ with the characteristic Eu²⁺ emission at 369 nm for 254 nm excitation. The thermoluminescence (TL) glow peak for LiCaAlF₆:Eu²⁺ was observed at around 180°C. The glow peak was about six times more intense compared with the dosimetric peak of the well known thermoluminescence dosimetric (TLD) phosphor LiF‐TLD 100. Thus this phosphor deserves much more attention than it has received until now and may be useful as a dosimetric material in radiation dosimetry. Copyright © 2015 John Wiley & Sons, Ltd.     

Calcium- and magnesium-binding properties of oncomodulin. Direct binding studies and microcalorimetry

Ca2+ binding to the wild type recombinant oncomodulin was studied by equilibrium flow dialysis in the absence and presence of 1, 2, and 10 mM Mg2+. Direct Mg2(+)-binding experiments were carried out by the Hummel-Dryer gel filtration technique. These studies revealed that in the absence of Mg2+ oncomodulin binds two Ca2+ with KCa = 2.2 x 10(7) and 1.7 x 10(6) M-1, respectively. In the absence of Ca2+ the protein binds only one Mg2+ with KMg = 4.0 x 10(3) M-1.Mg2+ antagonizes Ca2+ binding at the high affinity site according to the rule of direct competition. Ca2+ binding to the low affinity site is only slightly affected by Mg2+, so that in the presence of 2-3 mM Mg2+ the two sites have apparently an equal affinity for Ca2+. Microcalorimetry showed that, in spite of the different affinities of the two Ca2(+)-binding sites, delta H0 for the binding of each Ca2+ is identical and exothermic for -18.9 kJ/site. It follows that the entropy gain upon binding of Ca2+ is +77.1 J K-1 site-1 for the high affinity Ca2(+)-Mg2+ site and +56.0 J K-1 site-1 for the low affinity Ca2(+)-specific site. Mg2+ binding is endothermic for +13 kJ/site with an entropy change of +111 J K-1 site-1. The thermodynamic characteristics of the Ca2(+)-Mg2+ site resemble most those of site II (the so-called EF domain) of toad alpha-parvalbumin. The characteristics of Ca2+ binding to the specific site (likely the CD domain) are different from those of the Ca2+ specific sites in troponin C and in calmodulin and suggest that in oncomodulin hydrophobic forces do not play a predominant role in the binding process at the specific site.     

Circularly polarized emission studies on Tb3+ and Eu3+ complexes with potentially terdentate amino acids in aqueous solution.

Circularly polarized emission (CPE) and total emission (TE) spectra are reported for Eu3+ and Tb3+ complexes of L-aspartic acid (L-asp), L-serine (L-ser), L-threonine (L-thr) and L-histidine (L-his) in D2O solution under various pH conditions. Variations in TE and CPE intensities and in CPE splittings and sign patterns as functions of solution pH are correlated with lanthanide ion/ligand binding characteristics and with structural changes in the coordination environment of the metal ion. In the Eu3+/amino acid systems, the emission bands associated with the 5D0 leads to 7F1 and 7F2 Eu3+ transitions are monitored, and in the Tb3+/amino acid systems the 5D4 leads to 7F5 Tb3+ emission is examined.     

Eu2+‐induced enhancement of defect luminescence of ZnS

The Eu²⁺‐induced enhancement of defect luminescence of ZnS was studied in this work. While photoluminescence (PL) spectra exhibited 460 nm and 520 nm emissions in both ZnS and ZnS:Eu nanophosphors, different excitation characteristics were shown in their photoluminescence excitation (PLE) spectra. In ZnS nanophosphors, there was no excitation signal in the PLE spectra at the excitation wavelength λ_ex > 337 nm (the bandgap energy 3.68 eV of ZnS); while in ZnS:Eu nanophosphors, two excitation bands appeared that were centered at 365 nm and 410 nm. Compared with ZnS nanophosphors, the 520 nm emission in the PL spectra was relatively enhanced in ZnS:Eu nanophosphors and, furthermore, in ZnS:Eu nanophosphors the 460 nm and 520 nm emissions increased more than 10 times in intensity. The reasons for these differences were analyzed. It is believed that the absorption of Eu²⁺ intra‐ion transition and subsequent energy transfer to sulfur vacancy, led to the relative enhancement of the 520 nm emission in ZnS:Eu nanophosphors. In addition, more importantly, Eu²⁺ acceptor‐bound excitons are formed in ZnS:Eu nanophosphors and their excited levels serve as the intermediate state of electronic relaxation, which decreases non‐radiative electronic relaxation and thus increases the intensity of the 460 nm and 520 nm emission dramatically. In summary, the results in this work indicate a new mechanism for the enhancement of defect luminescence of ZnS in Eu²⁺‐doped ZnS nanophosphors. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and luminescence properties of Ca3(BO3)2:Eu3+ via two‐step method

Novel Ca₂B₂O₅·H₂O:Eu³⁺ nanotubes, constructed with nanobelts, were prepared using a hydrothermal method. The Ca₃(BO₃)₂:Eu³⁺ nanobelts with a thickness of about 100 nm were made for the first time using a two‐step hydrothermal process with Ca₂B₂O₅·H₂O:Eu³⁺ as the precursor. The samples were characterized by energy dispersive X‐ray spectroscopy, X‐ray diffraction, Fourier transform infra‐red spectroscopy, thermogravimetry differential thermal analysis and scanning electron microscopy. The relationship between Ca₃(BO₃)₂:Eu³⁺ and Ca₂B₂O₅·H₂O:Eu³⁺ was also studied. Possible reaction and growth mechanisms for Ca₂B₂O₅·H₂O:Eu³⁺ and Ca₃(BO₃)₂:Eu³⁺ were proposed. Ca₃(BO₃)₂:Eu³⁺ preserved the basic microstructure unit of Ca₂B₂O₅·H₂O:Eu³⁺. Both Ca₂B₂O₅·H₂O:Eu³⁺ and Ca₃(BO₃)₂:Eu³⁺ exhibited red emissions centred at 614 nm, but the maximum excitation peaks for Ca₂B₂O₅·H₂O:Eu³⁺ and Ca₃(BO₃)₂:Eu³⁺ differed. Ca₃(BO₃)₂:Eu³⁺ exhibited higher photoluminescence intensity but a lower R/O value than Ca₂B₂O₅·H₂O:Eu³⁺.     

Thermal quenching of luminescence of LiSr4(BO3)3:Eu2+ orange‐emitting phosphor

An orange‐emitting phosphor, Eu²⁺‐activated LiSr₄(BO₃)₃, was synthesized using the conventional solid‐state reaction. The photoluminescence excitation and emission spectra, and temperature dependence of the luminescence intensity of the phosphor were investigated. The results showed that LiSr₄(BO₃)₃:Eu²⁺ could be efficiently excited by incident light of 250–450 nm, and emits a strong orange light. With increasing temperature, the emission bands of LiSr₄(BO₃)₃:Eu²⁺ show an abnormal blue‐shift with broadening bandwidth and decreasing emission intensity. Copyright © 2013 John Wiley & Sons, Ltd.     

Optical properties of Eu2+/Eu3+ mixed valence phosphor Ca2SiO2F2:Eu2+/Eu3+

The Eu²⁺/Eu³⁺ mixed valence phosphor Ca₂SiO₂F₂:Eu²⁺/Eu³⁺ was prepared using a solid‐state reaction synthesis method in a CO atmosphere, and the optical properties were investigated. The spectroscopic properties revealed that Ca²⁺ ions were occupied by both Eu²⁺ and Eu³⁺ ions in Ca₂SiO₂F₂, and both ions were able to generate their characteristic emissions. A broad 5d → 4f Eu²⁺ band at ~470 nm and narrow 4f → 4f Eu³⁺ peaks upon excitation with n‐UV light were observed. The ratio between Eu²⁺ and Eu³⁺ emissions changed regularly, and the relative intensity of the red component from Eu³⁺ became systematically stronger with increasing overall Eu content. As a result, the emission color of these phosphors can be tunable from blue to pink under n‐UV light excitation.     

Synthesis and luminescence properties of cubic‐shaped Ca1‐xTiO3:Eu3+ particles

In this article Ca_1‐xTiO₃:xEu³⁺ single crystalline particles with a cubic morphology and average size of 248 to 815 nm were synthesized by a solvothermal method. The structural and optical properties of the Ca_1‐xTiO₃:xEu³⁺ cubes were investigated, the formation mechanism of the cubes were analyzed and discussed, and the influence of Eu doping content and cubic size on the photoluminescence were examined. The differences in the photoluminescence between Ca_1‐xTiO₃:xEu³⁺ cubic crystals and nanoparticles was analyzed. It was found that an addition of a small amount of water can substantially reduce the size of the cubes. An obvious red emission band centered at 615 nm was observed under the excitation at 395 nm for the cubes. Our results demonstrate CaTiO₃ cubes are good host materials for designing red phosphors.     

Study on luminescence properties of Ce3+ and Eu3+ ions in a nanocrystalline hexagonal Zn4Al22O37 novel system

The present communication is strongly focused on the investigation of synthesis, structural and luminescence properties of cerium (Ce³⁺)- and europium (Eu³⁺)-activated Zn₄Al₂₂O₃₇ phosphors. Ce³⁺- and Eu³⁺-doped Zn₄Al₂₂O₃₇ novel phosphors were prepared using a solution combustion synthesis route. Structural properties were studied using powder X-ray diffraction and high-resolution transverse electron microscopy. The optical properties were studied using ultraviolet–visible light spectroscopy and Fourier transform infrared spectroscopy; luminescence properties were studied using a photoluminescence (PL) technique. The crystal structure of the prepared Zn₄Al₂₂O₃₇ host and Ce³⁺- and Eu³⁺-activated Zn₄Al₂₂O₃₇ phosphors was investigated and was found to have a hexagonal structure. The measured PL emission spectrum of the Ce³⁺-doped Zn₄Al₂₂O₃₇ phosphor showed an intense and broad emission band centred at 421 nm under a 298 nm excitation wavelength. By contrast, the Eu³⁺-doped Zn₄Al₂₂O₃₇ phosphor exhibited two strong and intense emission bands at approximately 594 nm (orange) and 614 nm (red), which were monitored under 395 nm excitation. The Commission Internationale de l’Eclairage (CIE) colour coordinates of the Ce³⁺-doped Zn₄Al₂₂O₃₇ were investigated and found to be x = 0.1567, y = 0.0637 (blue) at 421 nm and for Eu³⁺-doped Zn₄Al₂₂O₃₇ were x = 0.6018, y = 0.3976 (orange) at 594 nm and x = 0.6779, y = 0.3219 (red) at 614 nm emission. The luminescence behaviour of the synthesized phosphors suggested that these phosphors may be used in lighting applications.