Investigation of the influence of silver and tin on the luminescence of trivalent europium ions in glass

Europium-doped aluminophosphate glasses prepared by the melt-quenching technique have been studied by photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). The effects of silver and tin doping, and of further thermal processing on Eu³⁺ ions luminescence have been assessed. For the glass system containing only europium, Eu³⁺ PL observed under UV excitation is suggested to occur through energy transfer from the excited glass host. After silver and tin doping, an enhanced UV excited Eu³⁺ PL has been indicated to occur essentially due to radiative energy transfer from isolated Ag⁺ ions and/or two fold-coordinated Sn centers. Since thermal processing of the material leads to a quenching effect on Eu³⁺ PL and Ag nanoparticles (NPs) formation due to reduction of silver ions by tin, XPS was employed in order to investigate the possibility for Eu³⁺→Eu²⁺ reduction during HT as a potential source of the PL decrease. The data points towards Ag NPs as main responsible for the observed weakening of Eu³⁺ PL.     

Synthesis and photoluminescence properties of YVO4:Eu3+, Al3+ phosphor

The Y_0.95?xAl_xVO₄:5%Eu³⁺ (0≤x≤0.1) phosphors were successfully synthesized by solid state reaction at 900 °C for 6 h, and their luminescence properties were investigated under UV and VUV excitation. Monitoring at 619 nm, a strong broad absorption was enhanced by co-doping of Al³⁺ into the YVO₄:Eu³⁺ lattices at 256 nm under UV excitation. The VUV excitation spectra also showed the enhanced excitation bands at about 156 and 200 nm. Under 254 or 147 nm excitation, it was found that Y_0.95?xAl_xVO₄:Eu³⁺(0≤x≤0.1) phosphors showed strong red emission at about 619 nm corresponding to the electric dipole ⁵D₀^–7F₂ transition of Eu³⁺. The improvement of luminescence intensity of YVO₄:Eu³⁺ was also observed after partial substituting Y³⁺ by Al³⁺ and the optimal luminescence intensity appeared with incorporation of 2.5 mol% Al³⁺.     

Synthesis and luminescence properties of a broad-band red phosphor Ca3Si2O7:Eu2+ for warm white light-emitting diodes

Single-phase broad-band red-emitting Ca₃Si₂O₇:Eu²⁺ phosphors, with photoluminescence features that qualify them as candidates for white light-emitting diodes applications, were successfully synthesized via a modified solid-state reaction method that employed H₃BO₃ as a flux. The phosphors produced have an intense broad red emission band, with a peak at 603 nm, a full width at half maximum of 110 nm, and color coordinates of (0.550, 0.438). Concentration quenching occurred at 0.01 mol Eu²⁺. The discussion of the results shows that Eu²⁺ ions should be accommodated at the Ca-sites of the lattice, dipole–dipole interactions should predominantly govern the energy transfer mechanism among them, and the critical distance between them is ～31 Å.     

Blue emission in Eu2+ activated MgXAl10O17 (X = Sr,Ca) phosphors

Here we reported photoluminescence properties of Eu²⁺ activated in novel and existing MgXAl₁₀O₁₇ (X = Sr, Ca) phosphor which has been prepared by combustion synthesis at 550 °C under UV and near UV excitation wavelength. The PL emission properties of MgSrAl₁₀O₁₇:Eu²⁺ were monitored at 254 nm and 354 nm respectively keeping emission wavelength at 469 nm. Whereas novel MgCaAl₁₀O₁₇:Eu²⁺ exhibit emission band at 452 nm keeping excitation at 378 nm. These blue emission corresponds to 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions. Further phosphor was analyzed by XRD for the confirmation of desired phase and purity.     

The influence of Eu3+ doping on photoluminescent properties of red emitting phosphor YInGe2O7:Eu3+ by microwave assisted and conventional sintering method

This paper describes an investigation of the crystalline morphology and photoluminescent properties of YInGe₂O₇ powders doped with different Eu³⁺ concentrations using microwave assisted sintering and conventional sintering. X-ray powder diffraction analysis confirmed the formation of monoclinic YInGe₂O₇ structure as YInGe₂O₇:Eu³⁺ powders were sintered at 1200 °C in microwave furnace for 1 h, and the raw material phase of Y₂O₃ was observed when Eu³⁺ concentration was below 30 mol%. Scanning electron microscopy showed microwave assisted sintering results in smaller particle size and more uniform grain size distribution. In the photoluminescent (PL) studies, the concentration quenching effect was observed under the excitation at 393 nm, but not under the excitation at CTS band. The ⁵D₀→⁷F₂ transition (620 nm), exhibits a non-exponential decay behavior as YInGe₂O₇:Eu³⁺ powders were sintered by microwave with the Eu³⁺ concentration higher than 50 mol%.     

Novel EGCG assisted ultrasound synthesis of self-assembled Ca2SiO4:Eu3+ hierarchical superstructures: Photometric characteristics and LED applications

This paper reports for the first time ultrasound, EGCG assisted synthesis of pure and Eu³⁺ (1–5 mol%) activated Ca₂SiO₄ nanophosphors having self-assembled superstructures with high purity. The shape, size and morphology of the product were tuned by controlling influential parameters. It was found that morphology was highly dependent on EGCG concentration, sonication time, pH and sonication power. The probable formation mechanism for various hierarchical superstructures was proposed. The PL studies of Ca₂SiO₄:Eu³⁺ phosphors can be effectively excited by the near ultraviolet (UV) (396 nm) light and exhibited strong red emission around 613 nm, which was attributed to the Eu³⁺ (⁵D₀ → ⁷F₂) transition. The concentration quenching phenomenon was explained based on energy transfer between defect and Eu³⁺ ions, electron–phonon coupling and Eu³⁺–Eu³⁺ interaction. The Judd–Ofelt intensity parameters and radiative properties were estimated by using PL emission spectra. The photometric studies indicate that the obtained phosphors could be a promising red component for possible applications in the field of white light emitting diodes.     

Photoluminescence properties of a new Eu2+-activated CaLaGa3S7 yellowish-green phosphor for white LED applications

A thiogallate chalcogenide phosphor CaLaGa₃S₇:Eu²⁺ was synthesized by a solid-state reaction at 950 °C in a H₂S atmosphere. The photoluminescence excitation,emission spectra, concentration quenching, fluorescence lifetime, and thermal quenching process of the phosphor were investigated in detail. It was found that the synthesized phosphor emitted intense and broadband yellowish-green light with a peak at 554 nm. Thus, the proposed phosphor is suitable for the development of blue or near UV LED. The critical dopant concentration of Eu²⁺ (R_c=15 Å) per unit formula was found to be 0.15 mol. At room temperature, the fluorescence lifetime of Eu²⁺ in CaLaGa₃S₇ was found to be 0.216 μs. The activation energy for thermal quenching was 0.29 eV. The chromaticity coordinates of our phosphor is very close in color to Y₃Al₅O₁₂:Ce³⁺. Therefore, CaLaGa₃S₇:Eu²⁺ can be a good alternative as a yellowish-green phosphor and can be used for white light generation in phosphor-converted LEDs.     

Scintillation kinetics and thermoluminescence of SrI2:Eu2+ single crystals

Single crystal of strontium iodide doped with 1% europium (SrI₂:1% Eu²⁺) was grown by Vertical Gradient Freeze technique. UV excited emission spectra were studied as a function of temperature. Results indicate the thermal quenching of Eu²⁺ emission starts from ～400 K with a thermal activation energy of 0.39 eV. Gamma and UV excited decay measurements indicate that the scintillation decay time of SrI₂:Eu²⁺ is longer than the lifetime of Eu²⁺ luminescence center in the SrI₂ host. The thermoluminescence glow curve revealed a highly concentrated charge carrier trap at 50 K. Elimination of this trap is expected to enhance the energy migration of charge carriers and result in faster scintillation decay.     

Luminescent properties of red-emitting LiSr4B3O(9−3x/2)Nx:Eu2+ phosphor for white-LEDs

An Eu²⁺-activated oxynitride LiSr_(4?y)B₃O_(9?3x/2)N_x:yEu²⁺ red-emitting phosphor was synthesized by solid-state reactions. The synthesized phosphor crystallized in a cubic system with space group Ia–3d. The LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphors exhibited a broad red emission band with a peak at 610 nm and a full width at half maximum of 106 nm under 410 nm excitation, which is ascribed to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The optimal doped nitrogen concentration was observed to be x=0.75. The average decay times of two different emission centers were estimated to be 568 and 489 ns in the LiSr_3.99B₃O_8.25N_0.5:0.01Eu²⁺ phosphors, respectively. Concentration quenching of Eu²⁺ ions occurred at y=0.07, and the critical distance was determined as 17.86 Å. The non-radiative transitions via dipole–dipole interactions resulted in the concentration quenching of Eu²⁺-site emission centers in the LiSr₄B₃O₉ host. These results indicate LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphor is promising for application in white near-UV LEDs.     

Optical properties,luminescence quenching mechanism and radiation hardness of Eu-doped GaN red powder phosphor

We report on the luminescence quenching mechanism of Eu-doped GaN powder phosphor produced with a low-cost, high yield rapid-ammonothermal method. We have studied as-synthesized and acid rinsed Eu-doped GaN powders with the Eu concentration of ～0.5 at.%. The Eu-doped GaN photoluminescence (PL) was investigated with 325 nm excitation wavelength at hydrostatic pressures up to 7.7 GPa in temperature range between 12 K and 300 K. The room temperature integrated Eu³⁺ ion PL intensity from acid rinsed material is a few times stronger than from the as-synthesized material. The temperature dependent PL studies revealed that the thermal quenching of the dominant Eu³⁺ ion transition (⁵D₀ → ⁷F₂) at 622 nm is stronger in the chemically modified phosphor indicating more efficient coupling between the Eu³⁺ ion and passivated GaN powder grains. Furthermore, it was found that thermal quenching of Eu³⁺ ion emission intensity can be completely suppressed in studied materials by applied pressure. This is due to stronger localization of bound exciton on Eu³⁺ ion trap induced by hydrostatic pressure. Furthermore, the effect of 2 MeV oxygen irradiation on the PL properties has been investigated for highly efficient Eu-doped GaN phosphor embedded in KBr–GaN:Eu³⁺ composite. Fairly good radiation damage resistance was obtained for 1.7 × 10¹² to 5 × 10¹³ cm^?2 oxygen fluence. Preliminary data indicate that Eu-doped GaN powder phosphor can be considered for devices in a radiation environment.     

Photoluminescence properties of red-emitting phosphors Ln3BWO9:Eu3+ (Ln=Y,La, Gd)

Undoped and Eu³⁺ activated Ln₃BWO₉ (Ln=Y, La, Gd) were prepared by the Pechini method and characterized with X-ray diffraction (XRD) and ultraviolet (UV) spectroscopy. All the samples have the hexagonal phase after heat treatment in the range of 850–1000 °C. The Eu³⁺ doped samples emit high-purity red light with peak maximum at about 617 nm under excitation of UV light (～285 nm) at room temperature. When the doping concentration of Eu³⁺ is about 20–30%, luminescence intensity reaches the maximum. Luminescence decay curves indicate that Ln₃BWO₉:Eu³⁺ exhibits a fast decay time of about 0.5 ms. A possible luminescence mechanism has also been proposed. It is worth noting that both the absorption of host lattice and the charge transfer (CT) transition of Eu³⁺ are of great importance to the promising luminescent performance of Ln₃BWO₉:Eu³⁺.     

Photoluminescence characterization of a novel red-emitting phosphor In2(MoO4)3:Eu3+ for white light emitting diodes

The red-emitting phosphor In₂(MoO₄)₃:Eu³⁺ with cubic crystal structure was synthesized by a conventional solid-state reaction technique and its photoluminescence properties were investigated. The prepared phosphor can be efficiently excited by ultraviolet (395 nm) and blue (466 nm) light. The emission spectra of the phosphor manifest intensive red-emitting lines at 612 nm due to the electric dipole ⁵D₀→⁷F₂ transitions of Eu³⁺. The chromaticity coordinates of x=0.63, y=0.35 (λ_ex=395 nm) and x=0.60, y=0.38 (λ_ex=466 nm) are close to the standard of National Television Standard Committee values (NTSC) values. The concentration quenching of In₂(MoO₄)₃:Eu³⁺ is 40 mol% and the concentration self-quenching mechanism under 466 nm excitation was the dd intereaction. As a result of the strong emission intensity and good excitation, the phosphor In₂(MoO₄)₃:Eu³⁺ is regarded as a promising red-emitting conversion material for white LEDs.     

Enhanced infrared to visible upconversion emission in Er3+ doped phosphate glass: Role of silver nanoparticles

Phosphate glasses with compositions (59.5–x)P₂O₅–MgO–xAgCl–0.5Er₂O₃ (0.0≤x≤1.5 mol%) containing fixed concentration of Er³⁺ ion with and without silver nanoparticles (NPs) are prepared using melt quenching technique. The amorphous nature of the glass is confirmed using the X-ray diffraction method. The homogeneous distribution of spherical Ag NPs (average size ～37 nm) in the glassy matrix is evidenced from the transmission electron microscopy (TEM) analyses. The UV–vis–NIR absorption spectra shows 10 bands corresponding to ⁴I_13/2, ⁴I_11/2, ⁴I_9/2, ⁴F_9/2, ⁴S_3/2, ²H_11/2, ⁴F_7/2, ⁴F_5/2, ²G_9/2, ⁴G_11/2 transitions in which the most intense bands are ²H_11/2 and ⁴G_11/2. The absorption spectrum of Er³⁺ ions free glass sample containing Ag NPs displays a prominent surface Plasmon resonance (SPR) band located at 528 nm. The infrared to visible frequency upconversion (UC) emission under 797 nm excitation shows two emission bands green (⁴S_3/2–⁴I_15/2) and red (⁴F_9/2–⁴I_15/2) centered at 540 nm and 634 nm, respectively, corresponding to Er³⁺ transitions. An enhancement in UC emission intensity of green band (⁴S_3/2–⁴I_15/2) is observed in the presence of silver NPs and the maximum enhancement occurred for 1.5 mol% AgCl. However, the enhancement of emission intensity of the red band (⁴F_9/2–⁴I_15/2) is smaller. The enhancement of UC emission is understood in terms of the intensified local field effect due to silver NPs.     

Effect of Na+ co-dopant and activator concentration on luminescent properties of CaGa4O7:Eu3+

Two series of calcium gallate phosphors: Ca_1?xEu_xGa₄O₇ and Ca_1?2xEu_xNa_xGa₄O₇ (x=0, 0.002, 0.01, 0.02, 0.03, 0.05) were synthesized by a modified Pechini method and their optical properties at 298 and 77 K were investigated. In undoped CaGa₄O₇ upon 255 nm excitation a bluish white emission (λ_max=500 nm) followed by an afterglow of the same color lasting for 10–20 s was observed. Eu³⁺-doping quenched the host-related luminescence and the characteristic red emission of the dopant with maximum at 613 nm appeared. Its excitation spectrum consisted of a broad band assigned to ligand to metal, O^2?→Eu³⁺, charge transfer absorption and narrow lines arising from intraconfigurational transitions within the 4f⁶ states of Eu³⁺ ion. The effects of Eu³⁺ concentration and Na⁺ co-doping on the luminescence properties and decay kinetics were studied. Low temperature emission spectra showed that Eu³⁺ ions are positioned in environments of different symmetries. Their relative populations changed with the activator content. Co-doping with Na⁺ ions led to a remarkable reduction of the number of Eu³⁺ sites as well as to noticeable improvement of the luminescence brightness though it did not affect the decay time of the emission. The quantum efficiencies of singly doped CaGa₄O₇:Eu³⁺ were very low (in the range of 1–3.7%). Na⁺ co-doping improved this parameter leading to the highest efficiency of 11% for CaGa₄O₇:3%Eu³⁺,3%Na⁺.     

Dual color emitting Eu doped strontium orthosilicate phosphors synthesized by bio-template assisted ultrasound for solid state lightning and display applications

A novel Sr₂SiO₄:Eu (1–5 mol %) superstructures (SS) were synthesized using bio-sacrificial A.V. gel assisted ultrasound method. Powder X-ray diffraction patterns confirmed the presence of both α and β phase formation. It was evident that the morphological growth was highly reliant on A.V. gel concentration, sonication time, pH and sonication power. The formation mechanisms for different hierarchical SS were proposed. From diffuse reflectance spectra, the energy band gap was estimated and found to be ∼4.70–5.11 eV. The photoluminescence emission spectra for the excitation at 392 nm, shows characteristic emission peaks at 593, 613, 654 and 702 nm which were attributed to ⁵D₀ → ⁷F₀, ⁷F_1, ⁷F₂ and ⁷F₃ transitions of Eu³⁺ ions respectively. Conversely, when the samples were subjected to the heat treatment at 850 °C for 3 h under argon atmosphere, display an intense broad emission peak with two de-convoluted peaks at 490 and 550 nm due to 4f⁶5d¹→4f¹ (⁸S_7/2) transitions of Eu²⁺ ions. The concentration quenching phenomenon was discussed which attributes to energy transfer, electron–phonon coupling and ion–ion interaction. The Judd–Ofelt intensity parameters and other radiative properties were estimated by using emission spectra. The CIE chromaticity coordinate values of Sr₂SiO₄:Eu²⁺ and Eu³⁺ nanophosphors were located in green and red regions respectively. The calculated CCT and CRI values specify that the present phosphor can be fairly useful for both green and red components of white LED’s. Luminescence decay and quantum yield suggest the suitability of this phosphor as an efficient luminescent medium for light emitting diodes. Overall, the results elucidated a rapid, environmentally benign, cost-effective and convenient method for Sr₂SiO₄:Eu³⁺ synthesis and for the possible applications such as solid state lighting and display devices.     

Preparation and luminescence properties of Eu2+-doped BaSi2O5 glass-ceramics

We report on the preparation of Eu²⁺-doped BaSi₂O₅ glass-ceramics by crystallizing an Eu³⁺-doped barium-silicate glass at temperatures in the range from 750 to 1100 °C. Single phase BaSi₂O₅ glass ceramics can be obtained by thermal annealing at temperatures of about 950 °C. The luminescence intensity of Eu²⁺ increases dramatically if monoclinic BaSi₂O₅ is formed. Monoclinic Eu²⁺:BaSi₂O₅ shows efficient, broad band luminescence between 450 and 550 nm by excitation in the near UV. Annealing at temperatures >1000 °C leads to orthorhombic BaSi₂O₅ with much smaller Eu²⁺ luminescence. Static and time-resolved luminescence measurements indicate that Eu²⁺ ions are incorporated into the BaSi₂O₅ crystallites while Eu³⁺ ions remain in the amorphous phase.     

Photoluminescence properties of Eu2+–Mn2+ codoped Ca-α-SiAlON phosphors

Eu²⁺–Mn²⁺ codoped Ca-α-SiAlON phosphors, Ca_0.736?ySi_9.6Al_2.4O_0.8N_15.2:0.064 Eu²⁺, yMn²⁺, were firstly synthesized by the high temperature solid state reaction method. The effects of doped Eu²⁺ and Eu²⁺–Mn²⁺ concentrations on the photoluminescence properties of the as-prepared phosphors were investigated systematically. Powder X-ray diffraction shows that pure Ca-α-SiAlON phase is synthesized after sintering at 1700 °C for 2 h under 0.5 MPa N₂ atmosphere. The excitation spectra of Eu²⁺-doped Ca-α-SiAlON phosphors are characterized by two dominant bands centered at 286 nm and 395 nm, respectively. The photoluminescent spectrum of Eu²⁺-doped Ca-α-SiAlON phosphor exhibits an intense emission band centered at 580 nm due to the allowed 4f ⁶5d→4f ⁷ transition of Eu²⁺, showing that the phosphor is a good candidate for creating white light when coupled to a blue LED chip. The intensities of both excitation and emission spectra monotonously decrease with the increment of codoped Mn²⁺ content (i.e. y value), indicating that energy transfer between Eu²⁺ and Mn²⁺ is inefficient in the case of Eu²⁺–Mn²⁺ codoped Ca-α-SiAlON phosphors.     

Synthesis and photoluminescent behavior of Eu3+-doped alkaline-earth tungstates

Eu³⁺-doped alkaline-earth tungstates MWO₄ (M=Ca²⁺, Sr²⁺, Ba²⁺) were prepared by a polymeric precursor method based on the Pechini process. The polymeric precursors were calcined at 700 °C for 2 h in order to obtain well-crystallized powders and then characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and photoluminescence spectroscopy (PL). All prepared samples showed a pure crystalline phase with scheelite-type structure confirmed by XRD. It was noted that the charge-transfer band shifted from 260 to 283 nm when calcium is replaced by strontium. However, this band was not observed for Eu³⁺-doped barium tungstate. Upon excitation at 260 nm, the emission spectra are dominated by the red ⁵D₀→⁷F₂ transition at 618 nm. By analyzing of the emission lines, it was inferred that Eu³⁺ ions occupy low symmetry sites in the host lattice. It was also found that Eu³⁺-doped SrWO₄ displays better chromaticity coordinates and greater luminescence intensity than the other samples.     

Absorption,luminescence, and electron paramagnetic resonance of molybdenum ions in CdWO4

A single crystal of cadmium tungstate (CdWO₄) containing approximately 200 ppm of molybdenum was grown by the Czochralski method and then characterized in a series of optical absorption, photoluminescence (PL), photoluminescence excitation (PLE), and electron paramagnetic resonance (EPR) experiments. The Mo⁶⁺ ions substitute for W⁶⁺ ions and serve as recombination sites for electrons and holes when the crystal is exposed to ionizing radiation. A charge-transfer absorption band for the Mo⁶⁺ ions was observed near 320 nm at 10 K. The PL experiments, performed at low temperature with 325 nm excitation, showed a Mo-associated emission peaking near 680 nm. A direct correlation of the 680 nm emission and the 320 nm absorption band was established by the PLE data. When these doped CdWO₄ crystals are exposed at low temperature either to light that is near or above the band gap or to X-rays, the Mo⁶⁺ ions can trap an electron and form stable Mo⁵⁺ ions. The EPR spectrum of the Mo⁵⁺ ions was observed at temperatures near 15 K, and a complete set of parameters describing the g matrix was obtained from an angular dependence study.     

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Bi(PO4)3 phosphors

A series of orange reddish emitting phosphors Eu³⁺-doped Sr₃Bi(PO₄)₃ have been successfully synthesized by conventional solid-state reaction, and its photoluminescence (PL) properties have been investigated. The excitation spectra reveal strong excitation bands at 392 nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr₃Bi(PO₄)₃:Eu³⁺ phosphors invariably exhibit five peaks assigned to the ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) transitions of Eu³⁺ and have dominating emission peak at 612 nm under 392 nm excitation. The luminescence intensity was enhanced with increasing Eu³⁺ content and the emission reached the maximum intensity at x=0.05 in Sr₃Bi(PO₄)₃:xEu³⁺. The energy transfer behavior in the phosphors was discussed. The Commission Internationale de lEclairage (CIE) chromaticity coordinates, the quantum efficiencies, and the decay curves of the entitled phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu³⁺-doped Sr₃Bi(PO₄)₃ phosphors are promising orange reddish-emitting phosphors pumped by near-UV light.