The blue-light emission enhancement mechanism of Eu in Eu, Dy: SiO2 matrix

A Eu, Dy co-doped SiO₂ matrix xerogel with blue emission was prepared by the sol–gel method. Strong blue emission located between 425 nm and 525 nm with a peak at 486 nm is observed under UV laser excitation at room temperature, which is related to a 4f → 5d energy transition of Eu²⁺. Such techniques as FT-IR and TGA–DSC were used to measure the microstructure of the luminescent materials. The influence of Dy³⁺ ions on the luminescent property of Eu²⁺ was investigated. The emission intensity of Eu, Dy-codoped samples is stronger than that of Eu doped samples. The emission enhancement mechanism relating to Eu²⁺ is attributed to an energy transfer involving Dy³⁺ → Eu²⁺. Using energy transition theory, we speculate that the mechanism may be one of the resonance transfers via multi-polar interactions, and present a possible energy transfer model. The Eu²⁺ blue emission intensity reaches the maximum when the Dy³⁺ concentration is 0.1 mol%. When the concentration of Dy³⁺ is 0.3 mol%, a fluorescence quenching appears which might be related to the overlap part of Eu²⁺ excitation and emission levels, and also suggests the existence of Eu²⁺ → Eu²⁺ energy transfer.     

Synthesis and luminescent characteristic of Eu-doped (Gd,Lu)2O3 nanopowders

Eu³⁺ doped (Gd,Lu)₂O₃ nanopowders with particle sizes ranging from 20 to 70 nm were synthesized by the co-precipitant method using mixed precipitants, namely the mixture of ammonium hydroxide (NH₃⋅H₂O) and ammonium hydrogen carbonate (NH₄HCO₃). The precipitate precursor prepared by this method was believed to possess a basic carbonate composition and its thermal decomposition of the (Gd,Lu)₂O₃:Eu³⁺ powders were investigated by Thermogravimetric analysis and differential thermal analysis (TG-DTA). This preparation was followed by a calcination process at 800-1100 °C and corresponding phosphor structure were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Photoluminescence measurement of the (Gd,Lu)₂O₃:Eu³⁺ particles show typical red emission at the 612 nm corresponding to the ⁵D₀ → ⁷F₂ transition. We found that the optimal Eu³⁺ molar doping concentration, calcined temperature and reaction time were 7 mol%, 1000 °C, and 2 h, respectively, which is helpful to obtain the final transparent ceramics with excellent properties.     

Rapid synthesis of pure and narrowly distributed Eu doped ZnO nanoparticles by solution combustion method

Pure ZnO:Eu³⁺ nanoparticles (~ 50 nm) were prepared by a solution combustion method. ZnO and Eu₂O₃ were used as starting materials and dissolved in nitric acid. Citric acid was used as a fuel. The reaction mixture was heated at 350 °C resulting into a rapid exothermic reaction yielding pure nanopowders. The atomic weight concentration of Eu³⁺ doped in ZnO was 20%. Transmission electron microscopy (TEM) was used to study the particle size and morphology. The nanopowders were characterized for phase composition using X-ray diffractrometry (XRD). Particle size distribution (PSD) analysis of ZnO: Eu³⁺ showed particle sizes ranging from 30 to 80 nm.The photoluminescence emission spectra of ZnO:Eu³⁺ nanostructures showed a strong band emission around 618 nm when excited with 515 nm wavelength.     

Basic study of Europium doped LiCaAlF6 scintillator and its capability for thermal neutron imaging application

Eu²⁺ 0.1, 0.5, 1, and 2 mol% doped LiCaAlF₆ single crystalline scintillators were grown by the micro-pulling down (μ-PD) method. Eu²⁺ 2 mol% doped LiCaAlF₆ was also prepared using the Czochralski method. In the transmittance spectra, 4f-5d absorption lines appeared around 200-220 and 290-350 nm. An intense emission at 375 nm due to Eu²⁺ 5d-4f transition was observed under ²⁴¹Am α-ray excitation. When ²⁵²Cf excited pulse height spectra were measured, Eu 2% doped one showed the highest light yield of 29,000 ph/n with 1.15 μs decay time. Using the 2 inchφ Czochralski grown one coupled with the position sensitive photomultiplier tube covered by Cd mask with various size (1, 2, 3, and 5 mm) pin holes, thermal neutron imaging was examined. As a result, the spatial resolution turned out to be better than 1 mm.     

Synthesis and Photoluminescence Properties of Eu3+‐Doped Silica@Coordination Polymer Core–Shell Structures and Their Calcinated Silica@Gd2O3:Eu and Hollow Gd2O3:Eu Microsphere Products

The conjugation of Eu³⁺‐doped coordination polymers constructed from Gd³⁺ and isophthalic acid (H₂IPA) with silica particles is investigated for the production of luminescent microspheres. A series of doping ratio‐controlled silica@coordination polymer core–shell spheres is easily synthesized by altering the amounts of metal nodes used in the reactions, where the ratios of Gd³⁺ and Eu³⁺ are 10:0 ( 1a ), 9:1 ( 1b ), 8:2 ( 1c ), 7:3 ( 1d ), 5:5 ( 1e ), and 0:10 ( 1f ). The formation of monodisperse uniform core–shell structures is achieved throughout the entirety of a series. Investigations of the photoluminescence property of the resulting series of silica@coordination polymer core–shell spheres reveal that 20% Eu³⁺‐doped product ( 1c ) has the strongest emission intensity. The subsequent calcination process on the silica@coordination polymer core–shell structures ( 1a ‐ f ) results in the formation of a series of doping ratio‐controlled silica@Gd₂O₃:Eu core–shell microspheres ( 2a ‐ f ) with uniform shell thickness. During the calcination step, the coordination polymers within silica@coordination polymer core–shells are transformed into metal oxides, resulting in silica@Gd₂O₃:Eu core–shell structures. The final etching process on the silica@Gd₂O₃:Eu core–shell microspheres ( 2a ‐ f ) produces a series of hollow Gd₂O₃:Eu microspheres ( 3a ‐ f ) as a result of the elimination of silica cores. The luminescence intensities of silica@Gd₂O₃:Eu core–shell ( 2a ‐ f ) and hollow Gd₂O₃:Eu microspheres ( 3a ‐ f ) also vary depending upon the doping ratio of Eu³⁺ ions.     

A study on the magnetic and photoluminescence properties of Eu(n+) and Sm3+ doped Fe3O4 nanoparticles

In this paper, Eu(n+), Sm3+ doped Fe3O4 nanoparticles were prepared via solvothermal method, in which Ferric chloride is used as the iron source, and anhydrous EuCl3, SmCl3 as doping source. Eu, Sm valence in doped Fe3O4 nanoparticles, and effects of Eu, Sm doping amount on their structure, morphology, magnetic properties and PL properties were discussed. The results show, the Eu ions had doped Fe3O4 nanoparticles in the mixed-valence state, when the Eu and Sm doping amount were increased, the doped Fe3O4 nanoparticles changed from hollow nanospheres into spherical particles, and finally changed into uniform cube-shaped particles with 13 nm in diameter. Moreover, the doping sites for doping ions in doped Fe3O4 nanoparticles were discussed from Rietveld analysis of XRD pattern of the doped Fe3O4 nanoparticles. And the changes of the magnetic and PL properties with the doping amount were further discussed. It was found that higher Sm(3+)-doping amount led to stronger magnetic dipole transitions, while the Eu(n+)-doping amount had little effect on the magnetic dipole transitions, thus resulting in different changes in their saturation magnetization with doping amount.     

Electro-deposition of Y2O3:Eu thin film phosphor and its luminescent properties

Y₂O₃:Eu³⁺ red-emitting thin film phosphor was prepared by a two-step process: the cathodical deposition of thin film of yttrium hydroxide and europium hydroxide followed by an annealing process to achieve Eu³⁺ doped Y₂O₃ film. It is found that the atomic content of Eu³⁺ can be well controlled by simply adjusting the volume ratio of Y(NO₃)₃ to Eu(NO₃)₃ solutions. Dependence of the photoluminescence intensity on the atomic content of Eu³⁺ in Y₂O₃ was also studied. The best photoluminescence performance of Y₂O₃:Eu³⁺ thin film phosphor was achieved as atomic content of Eu³⁺ equal to 1.85 at.%.     

Preparation and upconversion property of TeO2:Er/Yb nanoparticles

Different crystal structure of TeO₂ nanoparticles were used as the host materials to prepare the Er³⁺/Yb³⁺ ions co-doped upconversion luminescent materials. The TeO₂ nanoparticles mainly kept the original morphology and phase after having been co-doped the Er³⁺/Yb³⁺ ions. All the as-prepared TeO₂:Er³⁺/Yb³⁺ nanoparticles showed the green emissions (525 nm, 545 nm) and red emission (667 nm) under 980 nm excitation. The green emissions at 525 nm, 545 nm and red emission at 667 nm were attributed to the ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of the Er³⁺ ions, respectively. For the α-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles, three-photon process involved in the green (²H_11/2 → ⁴I_15/2) emission, while two-photon process involved in the green (⁴S_3/2→⁴I_15/2) and red (⁴F_9/2 → ⁴I_15/2) emissions. For the β-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles, two-photon process involved in the green (²H_11/2 → ⁴I_15/2), green (⁴S_3/2 → ⁴I_15/2) and red (⁴F_9/2 → ⁴I_15/2) emissions. It suggested that the crystal structure of TeO₂ nanoparticles had an effect on transition processes of the Er³⁺/Yb³⁺ ions. The emission intensities of the α-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles and β-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles were much stronger than those of the (α + β)-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles.     

YAG:Ce3+, Gd3+ nano-phosphor for white light emitting diodes

YAG:Ce³⁺, Gd³⁺ nano-phosphors were synthesised by the glycothermal method. The X-ray diffraction measurements showed that the samples can be well-crystallised at 600°C. The transition electron microscope showed that the particles have sizes mostly in the range between 35 and 100?nm. The YAG:Ce nano-phosphor had a wide emission band ranging from blue to yellow with a peak at 532?nm, due to the transition from the lowest 5d band to ²F_7/2, ²F_5/2 states of the Ce³⁺ ion. Red-shift of emission peak wavelength from 532 to 568?nm was achieved doping Gd³⁺ ions into the YAG:Ce³⁺ to substitute some Y³⁺ ions. White light emitting diodes (LEDs) were obtained by combining blue LED chip (InGaN-based 460?nm emitting) with (Y_{2.94? x} Ce_0.06Gd _x )Al₅O₁₂ phosphor. As x has the value of 0.8, an intense white LED with good colour rendering of 86 was obtained.     

Effective lattice stabilization of gadolinium aluminate garnet (GdAG) via Lu3+ doping and development of highly efficient (Gd,Lu)AG:Eu3+ red phosphors

Abstract

The metastable garnet lattice of Gd₃Al₅O₁₂ is stabilized by doping with smaller Lu³⁺, which then allows an effective incorporation of larger Eu³⁺ activators. The [(Gd_1?xLu_x)_1?yEu_y]₃Al₅O₁₂ (x = 0.1–0.5, y = 0.01–0.09) garnet solid solutions, calcined from their precursors synthesized via carbonate coprecipitation, exhibit strong luminescence at 591 nm (the ⁵D₀ → ⁷F₁ magnetic dipole transition of Eu³⁺) upon UV excitation into the charge transfer band (CTB) at ～239 nm, with CIE chromaticity coordinates of x = 0.620 and y = 0.380 (orange-red). The quenching concentration of Eu³⁺ was estimated at ～5 at.% (y = 0.05), and the quenching was attributed to exchange interactions. Partial replacement of Gd³⁺ with Lu³⁺ up to 50 at.% (x = 0.5) while keeping Eu³⁺ at the optimal content of 5 at.% does not significantly alter the peak positions of the CTB and ⁵D₀ → ⁷F₁ emission bands but slightly weakens both bands owing to the higher electronegativity of Lu³⁺. The effects of processing temperature (1000–1500 °C) and Lu/Eu contents on the intensity, quantum efficiency, lifetime and asymmetry factor of luminescence were thoroughly investigated. The [(Gd_0.7Lu_0.3)_0.95Eu_0.05]₃Al₅O₁₂ phosphor processed at 1500 °C exhibits a high internal quantum efficiency of ～83.2% under 239 nm excitation, which, in combination with the high theoretical density, favors its use as a new type of photoluminescent and scintillation material.     

(Eu-Nb)-codoped TiO2 nanopowders synthesized via Ar/O2 radio frequency thermal plasma oxidation processing: Phase composition and photoluminescence properties through energy transfer

(Eu³⁺-Nb⁵⁺)-codoped TiO₂ nanopowders have been prepared by Ar/O₂ radio frequency (RF) thermal plasma oxidizing liquid precursor mists, with various addition contents of dopants (molar ratio of Eu³⁺:Nb⁵⁺ = 1:1). Characterizations have been performed by the combined studies of XRD, TEM, Raman spectra, UV-vis spectroscopy, and excitation and PL spectra. The plasma-generated nanopowders mainly consist of anatase and rutile polymorphs. Doping Nb⁵⁺ cannot have appreciable influence on Eu³⁺ solubility (0.5 at.%) in the TiO₂ host lattice, but can significantly inhibit the increase of rutile weight fraction for TiO₂. 617 nm PL intensity at 350 nm indirect excitation through energy transfer is considerably weaker than that at 467 nm direct excitation, indicating that a defect state level in the TiO₂ host lattice might be lowered below the excited state of Eu³⁺ by doping Nb⁵⁺, which is conceivable from a relatively large amount of oxygen deficiencies yielded in the TiO₂ host lattice.     

Photoluminescence of Tb/Ce co-doped aluminum oxynitride powders

Aluminum oxynitride(AlON) phosphors co-doped by Tb³⁺ and Ce³⁺ were synthesized by nitridation of the precursor which was co-precipitated from Al(NO₃)₃ solution and nanosized carbon black at 1750 °C for 2 "hrs" in flowing nitrogen atmosphere. The obtained AlON based powders were composed of polycrystalline spinel typed particles with sizes in the range of 1-3 μm. Under an excitation of 275 nm, it was found that co-doping of Ce³⁺ could drastically enhance the luminescence of AlON:Tb³⁺ powder by energy transfer. The product with 0.5 mol% Ce³⁺ and 0.67 mol% Tb³⁺ exhibited a strong broad green emission at 540 nm. The critical quenching concentration of Tb³⁺ in AlON:0.5 mol% Ce³⁺/xmol% Tb³⁺ phosphor was determined to be 0.67 mol%. It was supposed that the mechanism of concentration quenching of Tb³⁺ in AlON:0.5 mol% Ce³⁺ xmol% Tb³⁺ phosphor was dipole-dipole interaction.     

A novel green luminescent material AlPO4:Tb

A novel green phosphor Tb³⁺ doped AlPO₄ was synthesized by conventional solid-state reaction method. The phosphor showed prominent luminescence in green due to the ⁵D₄-⁷F₅ transition of Tb³⁺. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis. The XRD measurements indicated that there are no crystalline phases other than AlPO₄. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 542 nm under UV excitation. It is shown that the 3 mol% of doping concentration of Tb³⁺ ions in AlPO₄:Tb³⁺ phosphor is optimum. The measured chromaticity for the phosphors AlPO₄:Tb³⁺ under UV excitation is (0.32, 0.53).     

Luminescent properties of Eu3+-doped α-NaYF4 single crystal under NUV-excitation

This paper reports on successful synthesis of α-NaYF₄ single crystal doped with Eu³⁺ at various concentrations by a modified Bridgman method. The crystal structure is characterized by means of X-ray diffraction. The absorption spectra, excitation spectra and emission spectra were measured to investigate the optical properties of the single crystals. An intense red emission located at 611 nm with long lifetime of 9.03 ms was observed in single crystal under the excitation of 394 nm light. It benefits from the low maximum phonon energy of α-NaYF₄ single crystal matrix (390 cm^?1). The CIE chromaticity coordinate of the α-NaYF₄ single crystal doped Eu³⁺ in 4 mol% concentration was calculated (x = 0.6055, y = 0.388), which was close to the National Television Standard Committee standard values for red phosphor (x = 0.67, y = 0.33). All these spectral properties suggest that that this kind of fluoride crystal with high thermal stability and high efficiency of red emission may be used as potential red phosphors for optical devices.     

Spectral analysis of Cu<Superscript>2+</Superscript> and Mn<Superscript>2+</Superscript> ions doped borofluorophosphate glasses

We report here on the development and spectral analysis of Cu²⁺ (0.5 mol%) and Mn²⁺ (0.5 mol%) ions doped in two new series of glasses. The visible absorption spectra of Cu²⁺ and Mn²⁺ glasses have shown broad absorption bands at 820 nm and 495 nm, respectively. For Cu²⁺ BFP glasses, excitation at 380 nm, a blue emission at 441 nm and also a weak emission at 418 nm ions have been observed. For Mn²⁺ ions doped BFP glasses, excitation at 410 nm and a red shift at 605 nm emission have been observed.     

Nanorods of white light emitting Sr2SiO4:Eu2+: microemulsion-based synthesis,EPR, photoluminescence,and thermoluminescence studies

White light emitting Sr₂SiO₄:Eu²⁺ nanoparticles were prepared using reverse micellar route using Tergitol as a surfactant. The systems were characterised by X-ray diffraction, scanning electron microscopy (SEM), photoluminescence, thermoluminescence (TL), and electron paramagnetic resonance (EPR) spectroscopy. SEM shows the formation of silicate nanorods. Two emission bands of bluish-green at 490 nm (S(I)) and of orange-red at 605 nm (S(II)) were observed. The two emission bands are assigned to the 4f–5d transition of Eu²⁺ ions in two different cation sites in α′-Sr₂SiO₄ orthorhombic lattices. Gamma-irradiated Sr₂SiO₄:Eu showed the presence of three TL glow peaks at 437, 487 K and weak peak at 540 K; however, no glow was observed in the undoped sample. Reduction of Eu³⁺ to Eu²⁺ is confirmed by EPR spectroscopy.     

Effects of Zn doping on the structural and luminescent properties of Sr4Si3O8Cl4:Eu phosphors

Sr₄Si₃O₈Cl₄: Eu²⁺ phosphors were synthesized by the solid-reaction at high temperature. The emission intensity reaches a maximum at 0.08 mol% of Eu²⁺ concentration. The present paper mainly focused on the effects of Zn²⁺ on the crystallization behavior and photoluminescence (PL) properties of Sr₄Si₃O₈Cl₄:0.08Eu²⁺. Results suggested that no new phase is introduced by co-doping with a small amount of Zn²⁺ ions, but when co-doped with excessive amount of Zn²⁺ ions, Sr₂ZnSi₂O₇ appears. We find that the co-doping of a small amount of Zn²⁺ could remarkably improve the PL intensity of Sr₄Si₃O₈Cl₄:0.08Eu²⁺. When x = 0.05, the intensity of Sr₄Si₃O₈Cl₄:0.08Eu²⁺,xZn²⁺ was increased up to 2.3 times that of pure Sr₄Si₃O₈Cl₄:0.08Eu²⁺, which could be attributed to the flux effect of Zn²⁺ ions, and the Zn²⁺ doping reduces the opportunities of the energy transfer between Eu²⁺.     

Influence of atmosphere on photoluminescence properties of Eu-doped ZnO nanocrystals

We have fabricated Eu³⁺-doped ZnO (ZnO:Eu) nanocrystals (NCs) by a reverse micelle method, and have studied their photoluminescence (PL) properties in vacuum, nitrogen gas, and oxygen gas atmospheres. The ZnO:Eu NCs exhibit the exciton, defect and Eu³⁺ PL under the inter-band photoexcitation of the ZnO host NCs. The intensity ratio among the three PL peaks is sensitive to the atmosphere for the PL measurements. We discuss the influence of the surrounding gas atmosphere to the PL properties.     

Novel blue-emitting phosphor NaMg4(PO4)3:Eu, Ce with energy transfer

A blue-emitting phosphor of NaMg₄(PO₄)₃:Eu²⁺, Ce³⁺ was prepared by a combustion-assisted synthesis method. The phase formation was confirmed by X-ray powder diffraction measurement. Photoluminescence excitation spectrum measurements show that the phosphor can be excited by near UV light from 230 to 400 nm and presents a dominant luminescence band centered at 424 nm due to the 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions at room temperature. Effective energy transfer occurs in Ce³⁺/Eu²⁺ co-doped NaMg₄(PO₄)₃ 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⁺, and Ce³⁺ plays a role as a sensitizer. Ce³⁺-Eu²⁺ co-doped NaMg₄(PO₄)₃ powders can possibly be applied as blue phosphors in the fields of lighting and display.     

Photoluminescent characterization of KNbO3:Eu

In this study, the photoluminescence (PL) spectra of europium-doped potassium niobate (KNbO₃) crystallites prepared by a vibrating milled solid-state reaction method were studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical spectral analysis (luminescence excitation, emission spectra and time-resolved spectra) were used to characterize the KNbO₃:Eu³⁺ powders. The results of the XRD revealed that the powders remained as a single orthorhombic structure at doping concentrations below 3 mol%. A second phase of EuNbO₄ begins to appear at 5 mol%. The ⁵D₀–⁷F₁ (593 nm) and ⁵D₀–⁷F₂ (614 nm) emission characteristics of Eu³⁺ appear at a quenching concentration of above 3 mol%. The Commission Internationale d’Eclairage (CIE) chromaticity coordinates of a Eu:KNbO₃ host excited at λ_ex = 400 nm and λ_ex = 466 nm wavelengths, both presented a red-shift when increasing the Eu³⁺ ion doping. The lifetime of the Eu³⁺ ion decreased as the doping concentration was increased from 1 to 7 mol%.