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⁺.     

Energy transfer induced Eu3+ photoluminescence enhancement in tellurite glass

In this work, structural, thermal and optical properties of Eu³⁺ doped TeO₂–La₂O₃–TiO₂ glass were investigated. The differential scanning calorimetry (DSC) measurements reveal an important stability factor ΔT=143.52 K, which indicates the good thermal and mechanical stabilities of tellurite glass. From the absorption spectrum, the optical band gap was found to be direct with E_g=3.23 eV. The temperature dependences of photoluminescence (PL) properties of Eu-doped and Eu–Tb codoped tellurite glass are investigated. As the temperature increases from 7 to 300 K, both the PL intensity and the PL lifetime relative to the ⁵D₂→⁷F₀ are nearly constant below 230 K and then an enhancement takes place. This anomalous feature is attributed to the thermally activated carrier transfer process from charged intrinsic defects states to Eu³⁺ energy levels.By co-doping tellurite glasses with Eu and Tb, a strong Eu³⁺ PL enhancement is shown due to excitation transfer from Tb³⁺ and intrinsic defects to Eu ions.     

Probing lattice defects in Sr2MgSi2O7:Eu2+,Dy3+

The Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ materials were prepared with a solid state reaction and their microscopic structure (at 295 K only) and luminescence were studied at selected temperatures between 150 and 295 K. Undisturbed Sr crystal planes were common in the TEM images of the undoped Sr₂MgSi₂O₇ material, whereas with Eu²⁺ doping more disturbed planes were observed even in the nanometer scale. With Dy³⁺ co-doping, a large number of small lattice domains created by the discontinuities in the crystal structure was observed. The domains with different orientations seem to be centered around point defects. The decay curves of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ showed fast (ms scale) persistent luminescence. The intensity of persistent luminescence increased considerably between 200 and 250 K while remaining constant in the ranges of 150–200 and 250–295 K. The changes were used to study the depth of the traps. In general, Dy³⁺ co-doping was found to deepen the traps.     

Upconversion photoluminescence properties of SrY2(MoO4)4:Er3+/Yb3+ phosphors synthesized by a cyclic microwave-modified sol–gel method

SrY_2−x(MoO₄)₄:Er³⁺/Yb³ phosphors with doping concentrations of Er³⁺ and Yb³⁺ (x = Er³⁺ + Yb³⁺, Er³⁺ = 0.05, 0.1, 0.2 and Yb³⁺ = 0.2, 0.45) have been successfully synthesized by a cyclic microwave-modified sol–gel method, and the upconversion photoluminescence properties have been investigated. Well-crystallized particles showed a fine and homogeneous morphology with particle sizes of 1–3 μm. Under excitation at 980 nm, SrY₂(MoO₄)₄:Er³⁺/Yb³⁺ particles exhibited a strong 525-nm, weak 550-nm emission bands in the green region, and a very weak 655-nm emission band in the red region. The possible mechanism of the green and red emissions was discussed in detail under consideration of a two-photon process. The Raman spectra of the particles indicated the presence of strong peaks at both higher and lower frequencies.     

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.     

Thermo,Iono and photoluminescence properties of 100 MeV Si7+ ions bombarded CaSiO3:Eu3+ nanophosphor

This paper reports on the thermo (TL), iono (IL) and photoluminescence (PL) properties of nanocrystalline CaSiO₃:Eu³⁺ (1–5 mol %) bombarded with 100 MeV Si⁷⁺ ions for the first time. The effect of different dopant concentrations and influence of ion fluence has been discussed. The characteristic emission peaks ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) of Eu³⁺ ions was recorded in both PL (1×10¹¹–1×10¹³ ions cm^?2) and IL (4.16×10¹²–6.77×10¹² ions cm^?2) spectra. It is observed that PL intensity increases with ion fluence, whereas in IL the peaks intensity increases up to fluence 5.20×10¹² ions cm^?2, then it decreases. A well resolved TL glow peak at ～304 °C was recorded in all the ion bombarded samples at a warming rate of 5 °C s^?1. The TL intensity is found to be maximum at 5 mol% Eu³⁺ concentration. Further, TL intensity increases sub linearly with shifting of glow peak towards lower temperature with ion fluence.     

Luminescence enhancement by the reduction–oxidation synthesis in monoclinic RE2O3 (RE=Eu,Gd) phosphors containing Eu3+ activator

A novel synthesis was developed for enhanced luminescence in sesquioxide phosphors containing Eu³⁺ activator. It consisted of two annealing steps: reduction under vacuum with gaseous H₂ at 10 Torr and 1300 °C and re-oxidation at 300–1500 °C in air. The integrated luminescence intensity of the monoclinic Eu₂O₃ phosphor was enhanced ca. 21 times by this method compared with conventional processing. The photoluminescence (PL) intensity was maximized at re-oxidation temperatures of 500–1100 °C. The PL characteristics of monoclinic Eu₂O₃ and Gd₂O₃:0.06Eu samples were compared with a commercial cubic Y₂O₃:Eu phosphor. The evolution of physical characteristics during the two-step annealing was studied by Raman spectroscopy, XPS, XRD, PL decay analysis, and SEM. PL decay lifetime increased proportionally to the PL intensity over the range 0.5–100 μs. Additional vibrational modes appeared at 490, 497, and 512 cm^?1 after the two-step annealing. The increase in PL intensity was ascribed to the formation of excess oxygen vacancies and their redistribution during annealing. Resonance crossovers between the charge transfer state and the emitting ⁵D_J states are discussed in relation to reported luminescence saturation mechanisms for oxysulfides Ln₂O₂S:Eu³⁺ (Ln=Y, La).     

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.     

Hydrothermal synthesis and the enhanced blue upconversion luminescence of NaYF4:Nd3+,Tm3+,Yb3+

Nd³⁺, Tm³⁺ and Yb³⁺ co-doped NaYF₄ upconversion (UC) material was synthesized by the hydrothermal method. The structure of the sample was characterized by the X-ray diffraction, and its UC luminescence properties were investigated in detail. Under the 980 nm semiconductor laser excitation, its UC spectra exhibited distinct emission peaks at 451 nm, 475 nm and 646 nm respectively. On the basis of the comparison of UC spectra between NaYF₄:Nd³⁺,Tm³⁺,Yb³⁺ and NaYF₄:Tm³⁺,Yb³⁺, it was indicated that the existence of Nd³⁺ ion enhanced the blue emission intensity. The law of luminescence intensity versus pump power proved that the blue emission at 475 nm, and the red emission at 646 nm were the two-photon processes, while the blue emission at 451 nm was a three-photon process.     

Synthesis and photoluminescence of Eu,Mg-alon phosphors by carbothermal reduction

Eu²⁺–Mg²⁺ co-doped alon phosphors were successfully prepared by carbothermal reaction at 1600 °C for 2 h and their structure and photoluminescence properties were studied. The lattice parameter increased with increasing Eu concentration, indicating the incorporation of Eu into alon crystal lattice. The pure alon phase was obtained when Eu concentration is below 0.2%. Compared with solid state reaction process, this method lead to less amounts of secondary phase, larger amounts of Eu²⁺ against Eu³⁺, smaller particle size, narrower particle size distribution and stronger luminescence intensity. The absolute emission intensity of obtained phosphor reached 82% relative to that of famous BAM: Eu²⁺ phosphor. The emission could be tuned widely from blue to green by varying carbon content.     

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.     

Microwave sol–gel derived NaCaGd(MoO4)3:Er3+/Yb3+ phosphors and their upconversion photoluminescence properties

Ternary molybdate NaCaGd_1−x(MoO₄)₃:Er³⁺/Yb³⁺ phosphors with the proper doping concentrations of Er³⁺ and Yb³⁺ (x = Er³⁺ + Yb³⁺, Er³⁺ = 0, 0.05, 0.1, 0.2 and Yb³⁺ = 0, 0.2, 0.45) were successfully synthesized by microwave sol–gel method for the first time. Well-crystallized particles formed after heat-treatment at 900 °C for 16 h showed a fine and homogeneous morphology with particle sizes of 3–5 μm. The optical properties were examined comparatively using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the doped particles exhibited a strong 525-nm emission band, a weak 550-nm emission band in the green region, which correspond to the ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions, and a very weak 655-nm emission band in the red region, which corresponds to the ⁴F_9/2 → ⁴I_15/2 transition. The optimal Yb³⁺:Er³⁺ ratio was obtained to be 9:1, as indicated by the composition-dependent quenching effect of Er³⁺ ions. The pump power dependence of upconversion emission intensity and Commission Internationale de L’Eclairage chromaticity coordinates of the phosphors were evaluated in detail.     

Lanthanide-doped strontium barium niobate (SBN) materials: A vibrational investigation

Vibrational Raman spectra have been measured for strontium barium niobate (Sr_0.5Ba_0.5Nb₂O₆, SBN50) single crystals and nanopowders doped with 1 mol% of the luminescent ions Eu³⁺ and Er³⁺. The nanocrystalline materials show slightly broader spectra with respect to the single crystals with the same composition. The presence of the Eu³⁺ and Er³⁺ ions at the 1 mol% doping level, and the present particle size (200 nm) do not appear to affect the ferro-to-paraelectric phase transition temperature typical of undoped SBN50 single crystals, as detected from anomalies in the dependence of the position of the Raman peak around 635 cm^?1 as a function of the temperature.     

Luminescent properties of Eu3+ and Sm3+ activated M2SiO4 (M=Ba,Sr and Ca) red-emitting phosphors for WLEDs

Eu³⁺ and Sm³⁺ activated M₂SiO₄ (M=Ba, Sr and Ca) red-emitting phosphors were synthesized by a solid state reaction. The results of XRD and SEM measurements show that the samples are single phase and have irregular shape. The excitation and emission spectra indicate that these phosphors were effectively excited by ultraviolet (395 nm) and blue (466 nm) light and exhibited red performance. The charge compensator R⁺ (R⁺=Li⁺, Na⁺ and K⁺) injecting into the host efficiently enhanced the luminescence intensity of the M₂SiO₄: Eu³⁺ and M₂SiO₄: Sm³⁺ phosphors. The emission intensity of M₂SiO₄: Eu³⁺ and Sm³⁺ doping Li⁺ were higher than that of Na⁺ or K⁺.     

The influence of some processing conditions on host crystal structure and phosphorescence properties of SrAl2O4:Eu2+, Dy3+ nanoparticle pigments synthesized by combustion technique

The spectroscopic and host phase properties of SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors with a series of different initiating combustion temperature, urea concentration as a fuel and critical pH of precursor solution are investigated. The SrAl₂O₄:Eu²⁺, Dy³⁺ nanoparticle pigments were obtained by exothermic combustion process within less than 5 min. The sample that ignited at initiating combustion temperature of 600 °C exhibits highest intensity emission peak at 517 nm in which the SrAl₂O₄ host phase has the maximum fraction of monoclinic SrAl₂O₄ phase. The excitation spectra consist of 240 and 254 nm broad peaks. The experimental results show that the optimum ratio of urea is 2.5 times higher than theoretical quantities for best emission condition of SrAl₂O₄:Eu²⁺, Dy³⁺ phosphor particles. The critical pH was obtained about 5.2. The crystallite size of these pigments is about 40 nm before thermal treatment and 62 nm after thermal treatment, respectively.     

Synthesis and near-infrared luminescence properties of LaOCl:Nd3+/Yb3+

Near-infrared emitting phosphors LaOCl:Nd³⁺/Yb³⁺ were prepared by the solid-state method, and their structures and luminescent properties were investigated by using X-ray diffraction and photoluminescence analysis, respectively. The studies shows that tetragonal LaOCl:Nd³⁺/Yb³⁺ can be synthesized by the solid-state reaction at 600 °C for 3 h. Upon 353 nm UV excitation, LaOCl:Nd³⁺/Yb³⁺ sample shows strong near-infrared emission lines in the region of 1060–1150 nm (corresponding to ⁴F_3/2 → ⁴I_J′ transition of Nd³⁺, J′ = 9/2, 11/2, 13/2, 15/2) and 980–1050 nm (corresponding to ²F_5/2 → ²F_7/2 transition of Yb³⁺). The decreasing emission intensity of Nd³⁺ with increasing doping concentration of Yb³⁺ proved the energy transfer in LaOCl:Nd³⁺/Yb³⁺. The possible near-infrared emission and energy transfer mechanism between Nd³⁺ and Yb³⁺, as well as the energy transfer efficiency of LaOCl:Nd³⁺/Yb³⁺ were discussed.     

Photoluminescence properties of Er-doped β-FeSi2 grown by ion implantation

Photoluminescence (PL) properties of Er-doped β-FeSi₂ (β-FeSi₂:Er) and Er-doped Si (Si:Er) grown by ion implantation were investigated. In PL measurements at 4.2 K, the β-FeSi₂:Er showed the 1.54 μm PL due to the intra-4f shell transition of ⁴I_13/2→⁴I_15/2 in Er³⁺ ions without a defect-related PL observed in Si:Er. In the dependence of the PL intensity on excitation photon flux density, the obtained optical excitation cross-section σ in β-FeSi₂:Er (σ=7×10⁻¹⁷ cm²) is smaller than that in Si:Er (σ=1×10^-15 cm²). In the time-resolved PL and the temperature dependence of the PL intensity, the 1.54 μm PL in β-FeSi₂:Er showed a longer lifetime and larger activation energies for non-radiative recombination (NR) processes than Si:Er. These results revealed that NR centers induced by ion implantation damage were suppressed in β-FeSi₂:Er, but the energy back transfer from Er³⁺ to β-FeSi₂ was larger than Si:Er.     

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⁺.     

Visible luminescence of nanocrystalline AlN:Er thin film by co-deposition of AlN,Er, and SiO2

We report a visible luminescence of Er³⁺ ions in an amorphous-nanocrystalline AlN:Er thin film prepared by co-deposition using AlN, Er, and SiO₂ targets. A PL emission spectrum of Er³⁺ in the AlN:Er film annealed at 750 °C showed a strong bluish green emission of Er³⁺ in the amorphous-nanocrystalline AlN:Er thin film, which is attributed to the intra-4fEr³⁺ transitions of ²H_11/2 → ⁴I_15/2 and ⁴F_7/2 → ⁴I_15/2. It was found that crystallite diameters were between 3 and 5 nm by high-resolution transmission electron microscopy. The occurrence of the strong Er³⁺ emission in the annealed AlN:Er thin film with a mixture of amorphous and nanocrystalline phases may be contributed to an increase in the number of excitation Er³⁺ centers and a presence of oxygen related to Er³⁺ excitation and recombination process in the AlN:Er thin film.     

Synthesis and luminescence of La2BaZnO5 phosphors

A modified synthesis of La₂BaZnO₅ phosphors activated with rare earths Eu³⁺, Tb³⁺, Pr³⁺ and Sm³⁺, and ns² ion Bi³⁺ is reported. RE₂BaZnO₅ compounds are conventionally prepared by two step solid state reaction. In the first step, carbonates or similar precursors are intimately mixed and heated at 900 °C to decompose the precursors to oxides. To eliminate the unwanted phases like BaRE₂O₄, the resulting powders are reheated at 1100 °C for long time. We prepared La₂BaZnO₅ phosphors activated with various activators by replacing the first step by combustion synthesis. Results on photoluminescence are presented. PL results on Eu³⁺ and Tb³⁺ are in good agreement with the literature reports. PL emission from Sm³⁺, Pr³⁺ and Bi³⁺ had not been reported earlier. Excitation spectrum of Eu³⁺ is dominated by a charge transfer band around 318 nm, while for the other rare earths a band at 240 nm is always present. This is attributed to the host absorption.