Effect of strontium additive on thermoluminescence properties of (Ba1-xSrxSO4)99.8%: Eu0.2% nanophosphor

Nanophosphors of barium strontium sulfate complex (Ba_1-xSr_xSO₄)_99.8%:Eu_0.2% (0 ≤ x ≤ 1) were prepared through the chemical co-precipitation method at room temperature. Precipitated samples were characterized using X-ray diffraction (XRD), dynamic light scattering (DLS) and high resolution transmission electron microscope (HRTEM) techniques. The obtained XRD patterns from the prepared nanophosphate series (Ba_1-xSr_xSO₄)_99.8%:Eu_0.2% exhibit an orthorhombic structure with semispherical particle shape. The lattice parameters of (Ba_1-xSr_xSO₄)_99.8%:Eu_0.2% solid crystals change and the cell volume decreases with the increase of x value of strontium. The thermoluminescence (TL) glow curves induced by gamma rays of (Ba_1-xSr_xSO₄)_99.8%:Eu_0.2% series were recorded and compared. The substitution of Ba²⁺ by Sr²⁺ cations shift the trap centers in the host of (Ba_1-xSr_xSO₄)_99.8%:Eu_0.2% material to the higher temperature side. The TL glow curve (GC) of sample with x = 0.12, with grain size ranging between 13–31 nm, reveals that it has deep trap centers, and higher TL sensitivity. The different heating rates effect of the glow peaks of samples with x = 0, 0.12 and 1 showed that they follow the first-order kinetics. These samples have been studied and analyzed with the help of both T_stop experimental method, and the computerized glow curve deconvolution (CGCD) program. T_m–T_stop experiment indicates that there are three trapping levels in both (BaSO₄)_99.8%:Eu_0.2% and (SrSO₄)_99.8%:Eu_0.2% sulfate samples at 452, 489, 543 K and 487, 513, 530 K respectively, while five peaks at 458, 486, 499, 544 and 556 K in the complex GC of (Ba_0.88Sr_0.12SO₄)_99.8%:Eu_0.2%. These values are used as input for CGCD. The figure of merit (FOM) during fitting procedures is determined.     

White-light generation through Ce3+/Mn2+-codoped and Eu2+-doped Ba1.2Ca0.8SiO4 T-phase phosphors

Hexagonal Ba_1.20Ca_0.8?2x?ySiO₄:xCe³⁺,xLi⁺,yMn²⁺ phosphors exhibit two emission bands peaking near 400 and 600 nm from the allowed f–d transition of Ce³⁺ ions and the forbidden ⁴T₁–⁶A₁ transition of Mn²⁺ ions, respectively. The strong interaction between Ce³⁺/Mn²⁺ ions is investigated in terms of energy transfer, crystal field effect, and microstructure by varying their concentrations. They show a higher quenching temperature of 250 °C than that of a commercially used (Ba,Sr)₂SiO₄:Eu²⁺ phosphor (150 °C). Finally, mixtures of these phosphors with green-emissive Ba_1.20Ca_0.70SiO₄:0.10Eu²⁺ are tested and yielded correlated color temperatures from 3500 to 7000 K, and color rendering indices up to 95%.     

Thermal expansion behavior and chemical compatibility of BaxSr1−xCo1−yFeyO3−δ with 8YSZ and 20GDC

Perovskite oxides of the composition Ba_xSr_1−xCo_1−yFe_yO_3−δ(BSCF) were synthesized via a modified Pechini method and characterized by X-ray diffraction, dilatometry and thermogravimetry. Investigations revealed that single-phase perovskites with cubic structure can be obtained for x ≤ 0.6 and 0.2 ≤ y ≤ 1.0. The as-synthesized BSCF powders can be sintered in several hours to nearly full density at temperatures of over 1180 °C. Thermal expansion curves of dense BSCF samples show nonlinear behavior with sudden increase in thermal expansion rate between about 500 °C and 650 °C, due mainly to the loss of lattice oxygen caused by the reduction of Co⁴⁺ and Fe⁴⁺ to lower valence states. Thermal expansion coefficients (TECs) of BSCF were measured to be 19.2–22.9 × 10^− 6 K^− 1 between 25 °C and 850 °C. Investigations showed further that Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ is chemically compatible with 8YSZ and 20GDC for temperatures up to 800 °C, above which severe reactions were detected. After being heat-treated with 8YSZ or 20GDC for 5 h above 1000 °C, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ was completely converted to phases like SrCoO_3−δ, BaCeO₃, BaZrO₃, etc.     

Crystal structure and photoluminescence of (Ba1−x−ySryEux)9Sc2Si6O24

Divalent europium-doped alkaline earth metal silicate phosphors, (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ (x=0.005–0.1, y=0–0.95), have been successfully prepared by solid-state reaction at 1350 °C. The analysis of X-ray diffraction shows that the compounds are in a single phase at the proper concentration of Sr²⁺. At room temperature, the Eu²⁺-activated Ba₉Sc₂Si₆O₂₄ phosphor exhibits a single emission band peaking at about 506 nm. With the increasing content of Sr²⁺, the luminescent intensity of (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ weakens, and the emission peak shifts towards red. Luminescence concentration quenching occurs when Eu²⁺ content x is more than 1 mol% in (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ (y=0/0.2). At low temperatures (Ba_0.9?ySr_yEu_0.1)₉Sc₂Si₆O₂₄ (y=0/0.2) phosphors have two emission bands corresponding to different Eu²⁺ crystallographic sites. The high energy peak (P₁) is quenched at room temperature, while the low energy peak (P₂) weakens much more slowly owing to the energy transfer from P₁ to P₂.     

Luminescent properties of Eu2+and Dy3+ ions in Ba4Al2O7 phosphor for solid state lighting

In this paper we report the combustion synthesis of rare earth (RE=Eu, Dy) doped Ba₄Al₂O₇ phosphors. Prepared phosphors were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), CIE color co-ordinates and their photoluminescence (PL) properties were also investigated. In case of Ba₄Al₂O₇: Eu²⁺, the emission spectra show unique band centered at 495 nm, which corresponds to the 4f⁶5d¹→4f⁷ transition of Eu²⁺, and PL emission spectra of Dy³⁺ ion under 348 nm excitation give two bands centered at 478 nm (blue) and 575 nm (yellow), which originate from the transitions of ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 of Dy³⁺, respectively. The results indicate that the Eu²⁺ and Dy³⁺ activated Ba₄Al₂O₇ phosphor could find application in solid state lighting.     

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⁺.     

Preparation,characterization and electrical property of Mn-doped ceria-based oxides

Manganese-doped ceria-based oxides, Ce_1−xMn_xO_2−δ (0.05 ≤ x ≤ 0.3) and Ce_1−x−yGd_xMn_yO_2−δ˙ (0.05 ≤ x≤ 0.2, 0.05 ≤ y ≤ 0.25) were synthesized, and crystal phase analysis by XRD and measurements of electrical properties were performed. Solubility limit of Mn in Ce_1−xMn_xO_2−δ˙ seemed to be between 5 mol% and 10 mol% and Mn₃O₄ was the main by-product above the solubility limit in the case of heat treatment at 1300 °C. Judging from the oxygen partial pressure dependence of total conductivity and emf measurements, Ce_1−xMn_xO_2−δ˙ is a single-phase mixed conductor within the composition below the solubility limit, and when the composition of Mn exceeds the solubility limit, it becomes the dual-phase mixed conductor of Ce_1−xMn_xO_2−δ˙ and Mn₃O₄. The doing of Mn in gadlia-doped ceria, Ce_1−x−yGd_xMn_yO_2−δ˙ (0.05 ≤ x ≤ 0.2, 0.05 ≤ y ≤ 0.25), was more difficult than that in CeO₂ presumably due to the preferential reaction between Gd and Mn to give GdMnO₃ to the GDC solid solution formation, and the Mn doping seems not to be so effective in preparing the mixed ionic–electronic conductor based on GDC.     

5D0→7F1 and 5D0→7F2 transition in europium doped halosulphates for mercury-free lamps

Polycrystalline Na₃SO₄F:Eu and NaMgSO₄F:Eu halosulphate phosphors prepared by a wet chemical method have been studied for its photoluminescence (PL) and thermoluminescence (TL) characteristics. Two well resolved peaks are observed at 593 nm and 614 nm, which are assigned to due to ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions of Eu³⁺ ions. TL is observed at temperatures between 100 °C and 300 °C. In this paper, we report PL emission spectra of Eu³⁺ and TL glow curves, which are more sensitive than the standard TLD-CaSO₄:Dy. The presented phosphors are applicable for the mercury free lamps and solid state lighting devices.     

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.     

Emission-tunable phosphors Ca9MgM′ (PO4)7: Eu2+,Mn2+ (M′=Li,Na, K) for white light-emitting diodes

A series of single-composition phosphors Ca₉MgM′(PO₄)₇:xEu²⁺, yMn²⁺ (CMM′ P:Eu²⁺, Mn²⁺; M′=Li, Na, K; 0.003≤x≤0.03; 0 ≤y≤0.1) were synthesized by solid state reactions. Upon excitation at 337 nm, phosphors Ca₉MgM′ (PO₄)₇: Eu²⁺ exhibit strong blue emissions centered at 417 (Ca₉MgLi(PO₄)₇:Eu²⁺), 457 (Ca₉MgNa(PO₄)₇:Eu²⁺), and 453 (Ca₉MgK(PO₄)₇:Eu²⁺) nm respectively, which correspond to the 4f⁶5d¹→4f⁷ transitions of Eu²⁺ ions, Through an effective resonance-type energy transfer, CMM′P:Eu²⁺,Mn²⁺ phosphors exhibit a series of colors by adjusting the concentration of Mn²⁺. The result indicates that CMM′P:Eu²⁺,Mn²⁺ can be potentially used as a UV excited phosphor for white light-emitting diodes (LEDs).     

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.     

Thermoluminescence response in gamma and UV irradiated Dy2O3 nanophosphor

Low temperature solution combustion method was employed to synthesize Dy₂O₃ nanophosphors using two different fuels (sugar and oxalyl dihydrazine (ODH)). Powder X-ray diffraction confirm pure cubic phase and the estimated particle size from Scherrer's method in sugar and ODH fuel was found to be 26 and 78 nm, respectively, and are in close agreement with those obtained using TEM and W–H plot analysis. SEM micrographs reveal porous, irregular shaped particles with large agglomeration in both the fuels. An optical band gap of 5.24 eV and 5.46 eV was observed for Dy₂O₃ for sugar and ODH fuels, respectively. The blueshift observed in sugar fuel is attributed to the particles size effect. Thermoluminescence (TL) response of cubic Dy₂O₃ nanophosphors prepared by both fuels was examined using gamma and UV radiations. The thermoluminescence of sugar used samples shows a single glow peak at 377 °C for 1–4 kGy gamma irradiations. When dose is increased to 5 kGy, two more shouldered peaks were observed at 245 and 310 °C. However, in TL of ODH used samples, a single glow peak at 376 °C was observed. It is observed that TL intensity is found to be more in sugar used samples. In UV irradiated samples a single glow peak at 365 °C was recorded in both the fuels with a little variation in TL intensity. The trapping parameters were estimated by different methods and the results are discussed.     

Studies on luminescence properties and energy transfer in Ce/Dy co-doped CaS nano-phosphors

Luminescence properties of CaS:Ce co-doped with dysprosium has been studied. Ce/Dy co-doped CaS nanophosphors (CaS:Ce_0.25Dy_0.75, CaS:Ce_0.50Dy_0.50, CaS:Ce_0.75Dy_0.25) were synthesized using the solid state diffusion method. The phase purity of the samples was confirmed using XRD data. The particle size was calculated using Debye–Scherrer formula and was found to be varying between 50 and 60 nm for all the three samples (CaS:Ce_0.25Dy_0.75, CaS:Ce_0.50Dy_0.50 and CaS:Ce_0.75Dy_0.25). TEM image analysis of CaS:Ce_0.50Dy_0.50 shows nearly spherical particles with diameter varying between 50 and60 nm. One way energy transfer from Dy³⁺ to Ce³⁺ in CaS host has been investigated using photoluminescence studies. Thermoluminescence of these nanophosphors has been studied for 0.5 Gy–21 kGy dose of gamma rays and the dose linearity of CaS:Ce_0.50Dy_0.50 has been compared with CaSO₄:Dy (standard TL dosimeter). Linear behavior over a large dose range between 0.5 Gy and 21 kGy was found for CaS:Ce_0.50Dy_0.50 as compared to CaSO₄:Dy (nanocrystalline and microcrystalline) but it is found to be less sensitive than microcrystalline CaSO₄:Dy. To identify the peaks of Ce³⁺ and Dy³⁺ in CaS, the TL spectra of CaS, CaS:Ce, CaS:Dy and CaS:Ce_0.50Dy_0.50 were recorded. The addition of dopants does not add new peaks in CaS but aid to enhance the TL emission. The peaks in CaS may be associated to intrinsic traps in the host lattice.     

Synthesis and characterization of layered Li1−x(Ni0.5Co0.5)1−yFeyO2(0 ≤ (1 − x) ≤ 1 and 0 ≤ y ≤ 0.2) cathodes

Layered Li(Ni_0.5Co_0.5)_1−yFe_yO₂ cathodes with 0 ≤ y ≤ 0.2 have been synthesized by firing the coprecipitated hydroxides of the transition metals and lithium hydroxide at 700 °C and characterized as cathode materials for lithium ion batteries to various cutoff charge voltages (up to 4.5 V). While the y = 0.05 sample shows an improvement in capacity, cyclability, and rate capability, those with y = 0.1 and 0.2 exhibit a decline in electrochemical performance compared to the y = 0 sample. Structural characterization of the chemically delithiated Li_1−x(Ni_0.5Co_0.5)_1−yFe_yO₂ samples indicates that the initial O3 structure is maintained down to a lithium content (1 − x) ≈ 0.3. For (1 − x) < 0.3, while a P3 type phase is formed for the y = 0 sample, an O1 type phase is formed for the y = 0.05, 0.1 and 0.2 samples. Monitoring the average oxidation state of the transition metal ions with lithium contents (1 − x) reveals that the system is chemically more stable down to a lower lithium content (1 − x) ≈ 0.3 compared to the Li_1−xCoO₂ system. The improved structural and chemical stabilities appear to lead to better cyclability to higher cutoff charge voltages compared to that found before with the LiCoO₂ system.     

High temperature properties of the n = 2 Ruddlesden–Popper phases (La,Sr)3(Fe,Ni)2O7−δ

The crystal chemistry and mixed conductor properties of the n = 2 member of the Ruddlesden–Popper (R–P) phases Sr_3−xLa_xFe_2−yNi_yO_7−δ with 0 ≤ x ≤ 0.3 and 0 ≤ y ≤ 1.0 have been studied at high temperature. High-temperature X-ray diffraction and thermogravimetric measurements of the equilibrium pO₂ (10^− 5 ≤ pO₂ ≤ 1 atm) in the temperature range 400 ≤ T ≤ 1000 °C indicate that the Sr₃FeNiO_7−δ phase is able to accommodate a large oxygen non-stoichiometry (δ ∼ 1.5) without structural transformations. The electrical conductivity and oxygen permeability increase with the substitution of Ni for Fe in the range 550 ≤ T ≤ 1000 °C. The electrical transport of the Sr₃FeNiO_7−δ phase is thermally activated and the activation energy decreases with the substitution of Ni for Fe for a given oxygen content. The increase in the oxygen permeation flux with increasing Ni content is due to an increasing oxygen non-stoichiometry and a lower activation energy for permeation.     

Proton diffusion in the superprotonic phase of [(NH4)1 − xRbx]3H(SO4)2 as studied by 1H spin-lattice relaxation

Proton diffusion in [(NH₄)_1 ? xRb_x]₃H(SO₄)₂ (0 < x < 1) has been studied by means of ¹H spin-lattice relaxation times, T₁. The relaxation times were measured at 200.13 MHz in the range of 296–490 K and at 19.65 MHz in the range of 300–470 K. In the high-temperature phase (phase I), translational diffusion of the acidic protons relaxes both the acidic protons and the ammonium protons. Spin diffusion averages the relaxation rate of the two kinds of protons, whereas proton exchange between them are slow. The spin-lattice relaxation times in phase I were analyzed theoretically, and parameters of proton diffusion were obtained. The mean residence time of the acidic protons increases with increase in x for [(NH₄)_1 ? xRb_x]₃H(SO₄)₂ (0 ≤ x ≤ 0.54). Rb₃H(SO₄)₂ does not obey this trend. The results of NMR well explain the macroscopic proton conductivity.     

A potential red-emitting phosphor with high color-purity for near-UV light emitting diodes

New red tungstates phosphors, Na₅La_1?xLn_x(WO₄)₄ (Ln = Eu, Sm) and Na₅Eu_1?xSm_x(WO₄)₄, were prepared by solid-state reaction technique. And their structure and photo-luminescent properties were investigated. The introduction of Sm³⁺ broadened the excitation band around 400 nm of the phosphors, and strengthened the red emission. And the possible energy transfer process from Sm³⁺ to Eu³⁺ is discussed. The single red LED was fabricated by combining InGaN chip with Na₅Eu_0.94Sm_0.06(WO₄)₄ as red phosphor, intense red light can be observed by naked eyes. Then the phosphor Na₅Eu_0.94Sm_0.06(WO₄)₄ may be a good candidate for red component of near-UV InGaN-based W-LEDs, because of efficient red-emitting with broadened absorption around 400 nm and appropriate CIE chromaticity coordinates (x = 0.65, y = 0.34).     

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.     

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.