Excitation Of Eu3 Research Articles

Studies on laser-assisted Penning ionization by the optogalvanic effect in Ne/Eu hollow cathode discharge

Laser-assisted Penning ionization (LAPI) is detected in a Ne/Eu hollow cathode (HC) discharge lamp using the pulsed optogalvanic (OG) method. In the Ne/Eu discharge, doubly ionized europium excited energy levels Eu[4f(7)(P(7/2,5/2)6)] lie within the thermal limit (∼kT) from the laser-excited neon's energy level [2p(5)(P3/202)3p or 2p(8) (in Paschen notation)] lying at 149,848 cm(-1). Therefore, Penning ionization (PI) of europium atoms likely to occur into its highly excited ionic states is investigated. To probe the PI of europium, the temporal profiles of its counterpart neon OG signal are studied as a function of discharge current for the transitions (1s(4)→2p(8)) and (1s(2)→2p(2)), corresponding to 650.65 and 659.89 nm wavelengths, respectively. It is observed that PI of europium alters the overall discharge characteristics significantly and, hence, modifies the temporal profile of the OG signals accordingly. The quasi-resonant ionizing energy transfer collisions between laser-excited Ne 2p(8) atoms and electronically excited europium P(9/2)10 atoms are used to explain the LAPI mechanism. Such LAPI studies carried out in HC discharge could be useful for the discharge of a metal-vapor laser with appropriate Penning mixtures.

Achieving visible light excitation in carbazole-based Eu3+–β-diketonate complexes via molecular engineering

A series of visible light excited Eu3+–carbazole based β-diketonate complexes has been developed by molecular engineering.

Near-UV light excited Eu3+, Tb3+, Bi3+ co-doped LaPO4 phosphors: Synthesis and enhancement of red emission for WLEDs

A series of single-phase Eu3+, Tb3+, Bi3+ co-doped LaPO4 phosphors were synthesized by solid-state reaction at 800°C. Crystal structures of the phosphors were investigated by X-ray diffraction (XRD). A monoclinic phase was confirmed. The excitation (PLE) and emission (PL) spectra showed that the phosphors could emit red light centered at 591nm under the 392nm excitation, which is in good agreement with the emission wavelength from near-ultraviolet (n-UV) LED chip (370–410nm). The results of PLE and PL indicated that the co-doped Tb3+ and Bi3+could enhance emission of Eu3+ and the fluorescent intensities of the phosphors excited at 392nm could reach to a maximum value when the doping molar concentration of Tb3+ and Bi3+ is about 2.0% and 2.0%, respectively. The co-doping Tb3+ and Bi3+ ions can strengthen the absorption of near UV region. They can also be efficient to sensitize the emission of Eu3+, indicating that the energy transfer occurs from Tb3+ and Bi3+ to Eu3+ ions. From further investigation it can be found that co-doping Tb3+ and Bi3+ ions can also induce excitation energy reassignment between 5D0–7F1 and 5D0–7F2 in these phosphors, and result in more energy assignment to 5D0–7F2 emission in LaPO4:Eu3+, Tb3+, Bi3+. Our research results displayed that La0.94PO4:Eu3+0.02, Tb3+0.02, Bi3+0.02 could be a new one and could provide a potential red-emitting phosphor for UV-based white LED.

Structure and photoluminescent properties of (200)-oriented Eu-doped CeO2 thin films fabricated on fused silica substrates by chemical solution deposition

(200)-oriented Eu-doped cerium oxide thin films were fabricated, on fused silica substrates by a chemical solution deposition method. The thin films obtained were characterized by X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and photoluminescence measurements. Ce with valence state 4+ is confirmed to be predominant in Eu-doped CeO2 thin films. All the thin films were dense and crack-free, and showed bright orange-red emissions under ultraviolet light excitation, originated from the 5D0→7F1 and 5D0→7F2 transitions of Eu3+ ions. Structure distortions induced by Eu-doping affected the light emission of electric dipole transition 5D0→7F2. The strongest photoluminescent intensity was observed in the thin films with a Eu-doping content x of 0.08, indicating the existence of concentration quenching effect of photoluminescence. Lifetime study of photoluminescence indicated that the decrease of lifetime was originated from augmented pathway for deactivating excited Eu3+ ions. Our study suggests that Eu3+-doped CeO2 thin films have potential applications in optoelectronic devices.

Red-shift of vanadate band-gap by cation substitution for application in phosphor-converted white light-emitting diodes

Eu3+ doped YVO4 is excellent traditional red phosphor, but shifting its efficient excitation band to a longer wavelength is necessary for application in white light-emitting diodes, and is a big challenge that calls for good solution. Following the observation that cation substitution usually is an effective way to manipulate the band-gap of phosphors, we carried out ab initio calculation for the band-gap of pure and Bi3+ doped LnVO4 (Ln = Y, Lu, and Sc). The results show that the band-gap decreases with the cationic radius from Y3+ to Sc3+, and the doping of Bi3+ further decreases their band-gaps. The experimental results on the Eu3+ doped and Eu3+, Bi3+ co-doped LnVO4 (Ln = Y, Lu, and Sc) phosphors confirm this. In particular, the excitation of Eu3+ and Bi3+ co-doped ScVO4 is shifted to approach 400 nm, which fulfills the excitation requirement of near-ultraviolet-based white light-emitting diodes, and implies that Eu3+ and Bi3+ co-doped ScVO4 should be a promising candidate as red phosphor in white light-emitting diodes.

Near-infrared frequency down-conversion and cross-relaxation in Eu2+/Eu3+–Yb3+ doped transparent oxyfluoride glass and glass–ceramics

In the present work, Eu2+/Eu3+–Yb3+ co-doped SiO2–K2O–BaF2–La2O3–Sb2O3 oxyfluoride glasses were synthesized by conventional melt quenching method to elucidate the cooperative energy transfer (CET) based frequency down conversion from Yb3+ ions under UV excitation. The in situ formation of divalent europium (Eu2+) along with Eu3+ during high temperature synthesis of these glasses under ambient atmosphere has been perceived and was explained through optical basicity model. Frequency down-conversion due to emission of two near infrared photons at around 1μm from Yb3+ ions has been realized upon excitation of Eu2+ ions under 286nm and further enhancement of this frequency down-conversion has been observed upon ceramization of these glasses. The precipitation of BaF2 nano-crystals in glass–ceramics causes reduction of Eu3+ ions to Eu2+ ions resulting in an enhancement in the cooperative energy transfer from Eu2+ to Yb3+. The weak contribution of Eu3+ excitation towards Yb3+ emission has been attributed to the cross-relaxation process via 5D0→7F6 (Eu3+):2F5/2→2F7/2 (Yb3+) route. The donor (Eu2+/Eu3+)–acceptor (Yb3+) concentration has been optimized at 0.5mol% Eu2O3 and 1.0mol% Yb2O3 to achieve maximum down-conversion intensity near 1μm.

Luminescence properties of Eu2 + and Ce3 + in Na5Ca2Al(PO4)4 produced by the combustion-assisted synthesis method

New greenish-blue luminescence Eu2+/Ce3+ codoped Na5Ca2Al(PO4)4 phosphors were prepared by a combustion-assisted synthesis method. X-ray powder diffraction analysis confirmed the formation of Na5Ca2Al(PO4)4 host lattice.. The Eu2+-doped Na5Ca2Al(PO4)4 sample has an efficient greenish-blue emission band that peaks at 476nm, while Ce3+-doped Na5Ca2Al(PO4)4 sample exhibits a strong emission band at 391nm. Efficient energy transfer from Ce3+ to Eu2+ occurs due to the large spectral overlap between the emission of Ce3+ and excitation of Eu2+. Co-doping Ce3+ enhances the emission intensity of Eu2+ greatly by transferring its excitation energy to Eu2+, and Ce3+ plays a role as a sensitizer. Ce3+/Eu2+ co-doped Na5Ca2Al(PO4)4 can possibly be applied as greenish-blue phosphors in the fields of lighting and display.

Impulsive excitation of mechanoluminescence in SrAl2O4:Eu, Dy phosphors prepared by solid state reaction technique in reduction atmosphere

The present paper reports the impulsive excitation of mechanoluminescence (ML) in SrAl2O4:Eu, Dy phosphor prepared by solid state reaction technique in a reduced atmosphere of 95% Ar+5% H2. The phosphors prepared exhibit such as intense ML that it can be seen in day light with naked eye. When a sample consisting of compact mass of the phosphor is deformed impulsively by the impact of a moving piston, then initially the mechanoluminescence intensity increases linearly with time, attains a peak value Im at a particular time tm, and later on it decreases with time, initially at a fast rate and then at a slow rate. The peak ML intensity Im and total ML intensity IT increase quardratically with the applied pressure and impact velocity. The ML spectra of SrAl2O4:Eu, Dy are found to be similar to the photoluminescence spectra. This result indicates that the ML is emitted from the Eu2+ ions as photoluminescence does. The ML intensity decreases with successive impact of the load onto the phosphors, whereby the diminished ML intensity can be recovered approximately by UV-irradiation. retain-->In the impulsive excitation, the complete recovery of ML intensity does not take place because the probability of radiative transition of luminescence centres formed near the newly created surfaces may decrease due the formation of surface traps. The values of tm, fast decay time and slow decay time do not change significantly with the impact velocity vo. The piezoelectrically-induced detrapping model is able to explain the characteristics of ML. According to this model, the local piezoelectric field near the activators causes the detrapping of electrons trapped in the negative oxygen vacancy and subsequently the detrapped electrons moving in the conduction band are captured by the Eu3+ ion, whereby the excited Eu2+ ions are produced and the subsequent de-excitation of excited Eu2+ ions gives rise to the light emission. It seems that, in addition to the change in crystal structure, in UV-irradiated SrAl2O4:Eu, Dy crystals, some localized electric dipoles present in the vicinity of Eu2+ ions may also enhance the piezoelectric constants of the crystals. The day light visible mechanoluminescence in SrAl2O4:Eu, Dy phosphors may be used for designing the impact stress and impact velocity sensors. Furthermore, the present investigation may be useful for determining the rise time of unknown pressure pulses and for determining the lifetime of charge carriers in shallow traps. The intense ML pulses may also be used in some specific photocatalytic reaction. The present study may also be helpful in preparing the ML-based light source by increasing the trap-depth of shallow traps. If the ML emission in certain materials will be in the ultraviolet range, then the ML pulses of short duration may be used to excite the phosphorescence and determining the decay time.

A novel green-emitting Ca15(PO4)2(SiO4)6:Eu2+ phosphor for applications in n-UV based w-LEDs

A novel green-emitting phosphor Eu2+-doped Ca15(PO4)2(SiO4)6 with a structure derivative of α′-Ca2SiO4 is synthesized by a conventional solid-state reaction method. The photoluminescence properties, the concentration quenching of Eu2+ ion, and the thermal stability are investigated. The Ca15(PO4)2(SiO4)6:Eu2+ phosphor is excited efficiently at a wavelength of 330 nm. At the optimum doping concentration of 0.5 mol% Eu2+ ion, the Ca15(PO4)2(SiO4)6:Eu2+ phosphor has the strongest emission intensity at 491 nm. The main mechanism of concentration quenching is found to be the rapid migration of excitation between the excited Eu2+ ions by exchange coupling. The thermal activation energy barrier is confirmed as 0.244 eV. Furthermore, the performance of this phosphor is tested by the fabrication of a phosphor-converted LED (pc-LED) through the integration of an InGaN-based near-ultraviolet light-emitting diode (LED) and driving under from 50 mA to 300 mA. The pc-LED reveals high color rendering index (CRI) value over 50, which is good for applications in w-LED.

Near-infrared quantum cutting in Eu2+, Yb3+ co-doped Sr3Gd(PO4)3 phosphor

An efficient Near-Infrared (NIR) quantum cutting (QC) in Eu2+–Yb3+ co-doped Sr3Gd(PO4)3 phosphor has been investigated. Upon excitation of Eu2+ with an ultraviolent (UV) photon at 343nm, two NIR emissions have been obtained from 2F7/2→2F5/2 transition of Yb3+. The luminescence spectra both in visible (VIS) and NIR regions and decay lifetime curves of Eu2+ have been measured to prove energy transfer (ET) from Eu2+ to Yb3+. The highest energy transfer efficiency (ETE) related to Yb3+ concentration was found to be 85.3%. So that the Sr3Gd(PO4)3 co-doped with Eu2+ and Yb3+ may be candidates to modify the spectral and improve the solar cell efficiency.

Anomalous susceptibility in single crystals of EuCo2Si2 with trivalent Eu: Influence of excited J multiplets

AbstractWe present a detailed study on the physical properties of single crystals of the Eu3+ intermetallic EuCo2Si2. The Eu valence was confirmed by X‐ray absorption. At low temperatures, the anisotropic susceptibility can be explained by a Eu3+ Van Vleck contribution with a crystal field parameter $V_{2}^{0} = 355\,{\rm K}$, but at high temperatures the data exceed the Van Vleck values significantly. This excess susceptibility is possibly related to the magnetic exchange between the excited Eu multiplets and the conduction band. A γ of 9.6 mJ K−2 mol and a Debye temperature of 322 K were estimated from the low temperature specific heat data. The compound does not undergo any phase transition in the temperature range 2–300 K.

Broadband near-infrared downconversion luminescence in Eu2+–Yb3+ codoped Ca9Y(PO4)7

An efficient broadband near-infrared (NIR) quantum cutting was demonstrated in Eu2+–Yb3+ codoped Ca9Y(PO4)7 phosphor. Upon excitation of Eu2+ ions to the 4f65d1 level with an ultraviolet photon at 322nm, emissions of two NIR photons at 983nm of Yb3+were achieved. The dependences of the visible and NIR emissions, the decay lifetime, the energy transfer efficiency (ETE), and the quantum efficiency (QE) on the Yb3+ doping content were investigated in detail. The results indicated that the maximum ETE and the corresponding downconversion QE can reach between 80% and 179%, respectively.

Sol-hydrothermal synthesis and optical properties of Eu3+, Tb3+-codoped one-dimensional strontium germanate full color nano-phosphors

Novel near-UV and blue excited Eu(3+), Tb(3+)-codoped one dimensional strontium germanate full-color nano-phosphors have been successfully synthesized by a simple sol-hydrothermal method. The morphologies, internal structures, chemical constitution and optical properties of the resulting samples were characterized using FE-SEM, TEM, HRTEM, EDS, XRD, FTIR, XPS, PL and PLE spectroscopy and luminescence decay curves. The results suggested that the obtained Eu(3+), Tb(3+)-codoped strontium germanate nanowires are single crystal nanowires with a diameter ranging from 10 to 80 nm, average diameter of around 30 nm and the length ranging from tens to hundreds micrometers. The results of PL and PLE spectra indicated that the Eu(3+), Tb(3+)-codoped single crystal strontium germanate nanowires showed an intensive blue, blue-green, green, orange and red or green, orange and red light emission under excitation at 350-380 nm and 485 nm, respectively, which may attributed to the coexistent Eu(3+), Eu(2+) and Tb(3+) ions, and the defects located in the strontium germanate nanowires. A possible mechanism of energy transfer among the host, Eu(3+) and Tb(3+) ions was proposed. White-emission can be realized in a single-phase strontium germanate nanowire host by codoping with Tb(3+) and Eu(3+) ions. The Eu(3+), Tb(3+)-codoped one-dimensional strontium germanate full-color nano-phosphors have superior stability under electron bombardment. Because of their strong PL intensity, good CIE chromaticity and stability, the novel 1D strontium germanate full-color nano-phosphors have potential applications in W-LEDs.

Tunable white light-emission of a CaW1−x Mo x O4:Tm3+, Tb3+, Eu3+ phosphor prepared by a Pechini sol–gel method

A white light-emitting CaW1−x Mo x O4:Tm3+, Tb3+, Eu3+ phosphor was prepared by a Pechini sol–gel method. The incorporation of Mo6+ into the CaWO4 host matrix can broaden its excitation range and promote tunability to its emission. When the CaW1−x Mo x O4 system is triply-doped with Tm3+, Tb3+, and Eu3+ ions, energy transfer occurs from both WO4 2− and MoO4 2− groups to Tm3+ and Tb3+ ions. A significant red-shift in the excitation of Eu3+ allows the resulting emission to be tunable between cool, natural, and warm white light by varying the excitation wavelength. The undoped and triply-doped CaW1−x Mo x O4 phosphors were characterized by X-ray diffraction, scanning electron microscopy, photoluminescence excitation and emission spectra, and CIE chromaticity (x, y) coordinates.

Speciation of Eu3+ bound to humic substances by time-resolved laser fluorescence spectroscopy (TRLFS) and parallel factor analysis (PARAFAC)

The bioavailability and toxicity of metal ions including radionuclides in the biosphere are greatly influenced by their speciation. Humic substances (HSs) are important constituents of various soil and water systems and have significant impact on the speciation and mobility of metal ions because of their high affinity to metal ions.In this study, the speciation of europium (Eu3+), a chemical homologue of trivalent actinides, with HSs collected from various origins was investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The difficulties associated with the separation of the contribution of different Eu3+ species due to overlapping spectra or similar fluorescence lifetimes were addressed and mitigated by applying a multi-mode factor analysis, parallel factor analysis (PARAFAC), which resulted in the number, spectra, decay curves and relative fluorescence intensity profiles of different Eu3+ species. Subsequently, the interpretation of the Eu3+ species, was tackled by principal component analysis (PCA) and partial linear square (PLS) regression to deduce the nature of the Eu3+ species by taking into account the physicochemical properties of the HSs.Three factors corresponding to different Eu3+ species were obtained at 70μM Eu3+ for all HSs investigated except for one humic acid. One of the factors corresponded to free Eu3+ ion interacting with HSs via diffusion. The remaining two factors were thought to be Eu3+ bound to HSs: one bound to acidic functional groups of HSs and the other to the sites of HSs influenced by the carbon backbone structures. It was also found that the latter factor exhibited strong energy transfer from the excited Eu3+ center to HSs. At lower Eu3+ concentration (10μM), two factors having similar fluorescent characteristics to those of the second and third factors were obtained.

Investigation on the Luminescence Improvement of Nanosized La2O3/Eu3+ Phosphor under Charge-Transfer Excitation

When the size of La2O3/Eu3+ phosphor decreases to the nanoscale, the rigidity of the lattice environment is decreased, causing the enlargement of the charge-transfer state (CTS) coordinate offset for the optical centers in La2O3/Eu3+ nanophosphor. The enlargement of the CTS coordinate offset results in the decrease of the CTS feeding probability to the 5D states of Eu3+ ions in the optical centers. In addition, the energy transfer to the quenching centers in the surface leads to the decrease of the 5D emission efficiency of the excited Eu3+ ions. In view of these two quenching mechanisms of the optical centers, proper surface coating is adopted to improve the luminescence efficiency for La2O3/Eu3+ nanophosphor under CT excitation. The changes in the related parameters of La2O3/Eu3+ nanophosphor in the surface coating and the subsequent annealing process have been experimentally determined and objectively analyzed. By surface coating, the luminescence efficiency of La2O3/Eu3+ nanophosphor has been signific...

Excitation of Eu3+ in gallium nitride epitaxial layers: Majority versus trap defect center

We report studies of the excitation mechanism of Eu ions in situ doped during organometallic vapor-phase epitaxy (OMVPE) of GaN. We find that the bright red emission under above-band gap excitation originates primarily from an incorporation site that exhibits high excitation efficiency but occurs in low relative abundance ( 97%).

Activation of a PARACEST agent for MRI through selective outersphere interactions with phosphate diesters.

Ln(S-THP)(3+) complexes are paramagnetic chemical exchange saturation transfer (PARACEST) agents for magnetic resonance imaging (MRI; S-THP = (1S,4S,7S,10S)-1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane, Ln(III) = Ce(III), Eu(III), Yb(III)). CEST spectra at 11.7 T show that the PARACEST effect of these complexes is enhanced at neutral pH in buffered solutions containing 100 mM NaCl upon the addition of 1-2 equiv of diethylphosphate (DEP). CEST images of phantoms at 4.7 T confirm that DEP enhances the properties of Yb(S-THP)(3+) as a PARACEST MRI agent in buffered solutions at neutral pH and 100 mM NaCl. Studies using (1)H NMR, direct excitation Eu(III) luminescence spectroscopy, and UV-visible spectroscopy show that DEP is an outersphere ligand. Dissociation constants for [Ln(S-THP)(OH(2))](DEP) are 1.9 mM and 2.8 mM for Ln(III) = Yb(III) at pH 7.0 and Eu(III) at pH 7.4. Related ligands including phosphorothioic acid, O,O-diethylester, ethyl methylphosphonate, O-(4-nitrophenylphosphoryl)choline, and cyclic 3,5-adenosine monophosphate do not activate PARACEST. BNPP (bis(4-nitrophenyl phosphate) activates PARACEST of Ln(S-THP)(3+) (Ln(III) = Eu(III), Yb(III)), albeit less effectively than does DEP. These data show that binding through second coordination sphere interactions is selective for phosphate diesters with two terminal oxygens and two identical ester groups. A crystal structure of [Eu(S-THP)(OH(2))]((O(2)NPhO)(2)PO(2))(2)(CF(3)SO(3)) x 2 H(2)O x iPrOH has two outersphere BNPP anions that form hydrogen bonds to the alcohol groups of the macrocycle and the bound water ligand. This structure supports (1)H NMR spectroscopy studies showing that outersphere interactions of the phosphate diester with the alcohol protons modulate the rate of alcohol proton exchange to influence the PARACEST properties of the complex. Further, DEP interacts only with the nonionized form of the complex, Ln(S-THP)(OH(2))(3+) contributing to the pH dependence of the PARACEST effect.

Ce3+→Eu2+ energy transfer mechanism in the Li2SrSiO4:Eu2+, Ce3+ phosphor

Abstract Ce3+/Eu2+ co-doped Li2SrSiO4 phosphor yields two emission bands consisted of blue and yellow components, which shows great potential as single host white phosphor for white LEDs. Effective energy transfer occurs in Ce3+/Eu2+ co-doped Li2SrSiO4 due to large spectral overlap between the emission of Ce3+ and excitation of Eu2+. Co-doping of Ce3+ enhances the emission intensity of Eu2+ greatly by transferring its excitation energy to Eu2+. The Ce3+ → Eu2+ energy transfer, thoroughly investigated by their absorption, excitation and photoluminescence decay behaviors, is demonstrated to be in the mechanism of electric dipole–dipole interaction.

Intermolecular Interactions as Actors in Energy-Transfer Processes in Lanthanide Complexes with 2,2′-Bipyridine

A series of lanthanide complexes [LnCl(x)(bpy)(y)(H(2)O)(z)]Cl(3-x)(H(2)O)(n)(EtOH)(m) (Ln = Eu, Gd, Tb; x = 1, 2; y = 1, 2; z = 2-4) with different numbers of 2,2'-bipyridine (bpy), chloride ions, and water molecules in the inner coordination sphere were synthesized and investigated with the aim of relating their molecular geometry and crystal packing to the efficiency of ligand-to-metal energy transfer. In conjunction to the rotation of the pyridine rings upon coordination to the Ln ion, the high flexibility displayed by bpy ligands leads to rather unexpected bending of these rings with respect to the central bond, owing to intermolecular interactions such as Cl...pi and pi-stacking ones. Deciphering the luminescence properties of the Eu and Tb complexes needs to take into account both the composition of the inner coordination sphere and the peculiarities of the crystal packing. For instance, in addition to the classical ligand --> Eu charge-transfer state (LMCT), another charge-transfer state induced by pi-stacking interactions (SICT) could be identified. These two states, located between the singlet and triplet states of the bpy ligand(s), provide relays facilitating the energy migration from the singlet to the triplet states and eventually to the excited Eu states, improving the overall ligand-to-Eu energy transfer. Another point is the involvement of the inner-sphere water molecules in H-bonding with chloride ions, which considerably lowers their luminescence quenching ability, so that the adducts remain highly luminescent. For instance, the terbium chloride with two bpy ligands is an efficient near-UV to green light converter, with an overall quantum yield equal to 37% despite the coordinated water molecules. The interpretations given are substantiated by DFT and TD-DFT theoretical calculations of the complexes and ligand assemblies.