Synthesis and photoluminescence properties of Eu doped Sr9Sc(PO4)7 phosphors for white light-emitting diodes

A series of Eu²⁺-activated Sr₉Sc(PO₄)₇ yellowish-green emitting phosphors were synthesized by conventional solid-state reaction. The photoluminescence (PL) properties and concentration quenching mechanism of the as-prepared phosphors were investigated. The emission spectrum exhibits a broad and asymmetric band peaking at 510 nm, which corresponds to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The excitation spectrum exhibits a broad band extending from 250 to 450 nm, which matches well with the emission of near ultraviolet (n-UV) chips (350–430 nm). Non-radiative transitions between Eu²⁺ ions in the Sr₉Sc(PO₄)₇ host have been demonstrated to be attributable to dipole–dipole interactions, and the critical distance was calculated to be 23.1 Å. These results indicate that Sr₉Sc(PO₄)₇:Eu²⁺ phosphor could serve as a promising candidate for application in n-UV white-light LEDs.     

Preparation of Ca4Mg5(PO4)6:Eu,Mn phosphor and its photoluminescence properties

Eu²⁺ and Mn²⁺ singly doped and Eu²⁺/Mn²⁺-codoped Ca₄Mg₅(PO₄)₆ phosphors were synthesized via combustion synthesis. Mn²⁺-singly doped Ca₄Mg₅(PO₄)₆ phosphor exhibits a single red emission in the wavelength range of 500–700 nm due to the ⁴T₁(⁴G)→⁶A₁(⁶S) transition of Mn²⁺. Eu²⁺/Mn²⁺ co-doped phosphor emits two distinctive luminescence bands: a blue one centered at 442 nm originating from Eu²⁺ and a broad red-emitting one peaked at 609 nm from Mn²⁺. Energy transfers from Eu²⁺ to Mn²⁺ were discovered by directly observing significant overlap of the excitation spectrum of Mn²⁺ and the emission spectrum of Eu²⁺ as well as the systematic relative decline and growth of emission bands of Eu²⁺ and Mn²⁺, respectively. Based on the principle of energy transfer, the relative intensities of blue and red emission could be tuned by adjusting the contents of Eu²⁺ and Mn²⁺.     

White light emission from Eu co-activated Ca2Gd8Si6O26:Dy nanophosphors by solvothermalsynthesis

Ca₂Gd₈(SiO₄)₆O₂ (CGS) nanophosphors with different concentrations of single-doped Dy³⁺ ions and co-doped Dy³⁺/Eu³⁺ ions were prepared by a solvothermal synthesis. Very fine particles in the nanometer range could be achieved by this method, as evidenced by transmission electron microscope measurements. The hexagonal phase of the oxyapatite structure was confirmed by X-ray diffraction patterns. The energy transfer between Eu³⁺ and Dy³⁺ ions was investigated by photoluminescence excitation and emission properties. These phosphors had absorption bands in the UV and NUV region, which are suitable for the emission wavelength of UV or NUV light-emitting diodes (LEDs). With increasing the Eu³⁺ ion concentration, the emission peak intensity corresponding to the ⁵D₀→⁷F₂ transition increased and the yellow (⁴F_9/2→⁶H_13/2) emission intensity also increased compared to the blue (⁴F_9/2→⁶H_15/2) emission intensity due to the increased energy transfer between Dy³⁺ to Eu³⁺ ions. Thus, the Eu³⁺ ions compensated the red emission component of the Dy³⁺ doped CGS nanophosphors. Such phosphors are expected to have potential applications for NUV based white LEDs.     

Structural and luminescence properties of RE (RE = Eu, Tb):(MgCa)2Bi4Ti5O20 ceramics

Rare-earth ions (Eu³⁺, Tb³⁺) activated magnesium calcium bismuth titanate [(MgCa)₂Bi₄Ti₅O₂₀] ceramics were prepared by conventional solid state reaction method for their structural and luminescence properties. By using XRD patterns, the structural properties of ceramic powders have been analyzed. Emission spectrum of Eu³⁺:(MgCa)₂Bi₄Ti₅O₂₀ ceramic powder has shown strong red emission at 615 nm (⁵D₀ → ⁷F₂) with an excitation wavelength λ_exci = 393 nm and Tb³⁺:(MgCa)₂Bi₄Ti₅O₂₀ ceramic powder has shown green emission at 542 nm (⁵D₄ → ⁷F₅) with an excitation wavelength λ_exci = 376 nm. In addition, from the measurements of scanning electron microscopy (SEM), Fourier transform-infrared (FTIR) and energy dispersive X-ray analysis (EDAX) results the morphology, structure and elemental analysis of these powder ceramics have been studied.     

Influence of porosity on the electrical properties of La9.33(SiO4)6O2 oxyapatite

Oxyapatites are very promising materials in terms of ionic conductivity. They can be considered as a potential electrolyte for fuel cells as SOFC. The influence of porosity on the electrical properties of La_9.33(SiO₄)₆O₂ oxyapatite is reported here. Hot pressed pellets with various densification ratios have been characterized by the complex impedance method. The high frequency response associated with the bulk contribution is much more affected by the porosity than the grain boundaries contribution: as a consequence, the electrical behaviour of the samples has been considered in assimilating the porous ceramics to composite materials made of apatite with various amounts of air inclusions. Thus, the porosity dependence of conductivity, activation energy and permittivity are reported here. A percolation threshold has been highlighted for porosity values greater than 30%, involving great lowering of the electrical performances.     

The luminescence spectroscopy and thermal stability of red-emitting phosphor Ca9Eu(VO4)7

Eu-based vanadate Ca₉Eu(VO₄)₇ phosphor was synthesized by the solid state reaction method and was characterized by X-ray powder diffraction (XRD). The photoluminescence excitation and emission spectra, fluorescence decay curves and the dependence of luminescence intensity on temperature were investigated. The phosphor can be efficiently excited by near UV light to realize an intense red luminescence (614 nm) corresponding to the electric dipole transition ⁵D₀ → ⁷F₂ of Eu³⁺ ions. The crystallographic site-occupations of the Eu³⁺ ions in Ca₉Eu(VO₄)₇ were investigated by the site-selective excitation and emission spectra, and the fluorescence decay curves in the ⁵D₀ → ⁷F₀ region using a pulsed, tunable, narrowband dye laser. The red luminescence together with the thermal stability was discussed on the base of the Eu³⁺ site-distribution in Ca₉Eu(VO₄)₇ host.     

Synthesis of (Sr0.85Zn0.15)3(PO4)2:Eu by a modified solid-state reaction and its luminescent properties for ultraviolet light emitting diodes

Using urea, boric acid and polyethylene glycol (PEG) as auxiliary reagents, the novel red emitting phosphors (Sr_0.85Zn_0.15)₃(PO₄)₂:Eu³⁺ have been successfully synthesized by a modified solid-state reaction. The material has potential application as a fluorescent material for ultraviolet light-emitting diodes (UV-LEDs). The dependence of the properties of (Sr_0.85Zn_0.15)₃(PO₄)₂:Eu³⁺ phosphors upon urea, boric acid and the PEG concentration and the quadric sintered temperature were investigated. The crystallization and particle sizes of (Sr_0.85Zn_0.15)₃(PO₄)₂:Eu³⁺ have been investigated by using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Luminescent measurements showed that the phosphors can be efficiently excited by ultraviolet (UV) to visible region, emitting a red light with a peak wavelength of 616 nm. The results show that the boric acid, urea and the PEG were effective in improving the fluorescent intensity of (Sr_0.85Zn_0.15)₃(PO₄)₂:Eu³⁺ and the optimum molar ratio was 0.1, 8 and 0.021, respectively.     

Preparation of Sr2SiO4:Eu phosphors by microwave-assisted sintering and their luminescent properties

An Eu³⁺ activated strontium silicate phosphor was synthesized using a microwave-assisted sintering with a flux NH₄Cl. X-ray powder diffraction analysis confirmed the formation of pure Sr₂SiO₄ phase without second phase or phases of starting materials as Sr_1.9SiO₄:Eu³⁺_0.1 powders sintered at various temperatures in microwave furnace for 1 h. Scanning electron microscopy showed smaller particle size and more uniform grain size distributions are obtained by microwave-assisted sintering. In the PL studies, the excitation spectrum of Sr_1.9SiO₄:Eu³⁺_0.1 phosphors exhibited a broad band in the UV region centered at about 270 nm which was consistent with the absorption spectra. Both microwave sintered and conventionally sintered powders emitted a maximum luminescence centered at 617 nm under excitation of 395 nm, with similar luminescent intensity. The results showed that microwave processing has the potential to decrease the sintering time and required energy input for the production of Sr_1.9SiO₄:Eu³⁺_0.1 phosphors without degrading photoluminescence.     

Sol-gel derived nanosized Sr5(PO4)2SiO4 powder with enhanced in vitro osteogenesis and angiogenesis for bone regeneration applications

Bioactive glass ceramics are widely used for hard tissue repair and bone regeneration due to their most attractive properties such as biocompatibility, bioactivity and non toxicity. In this study, for the first time, sol-gel method was used to synthesize nanosized strontium phosphosilicate (SPS: Sr₅(PO₄)₂SiO₄) with rod shaped morphology by using CTAB as a surfactant. The obtained SPS powder was characterized by FTIR, XRD, Raman, SEM-EDS and TEM analysis. In vitro bioactivity study confirms that SPS possesses bone bonding ability by formation of amorphous apatite layer on its surface. In vitro osteogenesis and angiogenesis studies were performed on SPS powder to determine its biological responses using mBMSCs and HUVECs, respectively. The co-culture of BMSCs with different concentrations of SPS powder (50, 100, 150, 200 and 250?µg/ml) reveals that there's no any cytotoxicity effect on mBMSCs and observed good cell proliferation, alkaline phosphatase activity, calcium nodules formation, osteogenesis-related gene expressions (alp, runx2, col1a2 and ocn). In addition, the angiogenesis study demonstrated that SPS powder can stimulate the cellular response of HUVECs and its gene expressions (vegfr2 and hif1α-3). Therefore, these results confirm that nanosized SPS could act as promising bioceramic material for bone tissue engineering applications.     

Effect of Eu doping on structure and electrical properties of lead-free (Bi0.5Na0.5)0.94Ba0.06TiO3 ceramics

Eu-doped (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNBT6-xEu, x=0.00–2.00 at%) lead-free piezoelectric ceramics have been synthesized by the solution combustion method. The effect of Eu doping concentration on the phase structure, microstructure and electrical properties of BNBT6 ceramics has been investigated. The XRD analysis confirms that the europium additive incorporates into the BNBT6 lattice and results in a phase transition from the coexistence of rhombohedral and tetragonal phases to a more symmetric pseudocubic phase. The SEM images indicate that the europium additive has little effect on the ceramic microstructure and the average grain size is about 2.0 μm. The electrical properties of BNBT6 ceramics can be improved by appropriate Eu doping. The 0.25 at% Eu doped BNBT6 ceramic presents excellent electrical properties: piezoelectric constant d₃₃=149 pC/N, remnant polarization P_r=40.27 μC/cm², coercive field E_c=2.95 kV/mm, dielectric constant ε_r=1658 and dissipation factor tan δ=0.0557 (10 kHz).     

Sr0.5Zr2(PO4)3陶瓷的力学性能研究

用共沉淀法和低分子有机溶剂分散获得SZP粉体,经干压成型和烧结得到SZP陶瓷.研究了其力学性能与烧结温度烧结时间和添加剂用量的关系.最佳工艺条件为添加MgO6wt%,1300℃或ZnO3wt%,1200℃均烧结1.5小时,SZP陶瓷的抗压强度分别可达244.0MPa和226.2MPa.     

Highly uniform Gd(OH)3 and Gd2O3:Eu hexagram-like microcrystals: glucose-assisted hydrothermal synthesis,growth mechanism and luminescence property

Monodispersed and uniform Gd(OH)₃ microcrystals with novel hexagram-like morphology have been successfully prepared through a simple and green hydrothermal process with the assistance of glucose. The results of control experiments revealed that the glucose concentration in the reaction system was an important factor, which affected the morphology of the Gd(OH)₃ microcrystals significantly. On the basis of time-dependent experiments, the growth mechanism of the Gd(OH)₃ hexagrams was discussed. Furthermore, the Gd₂O₃ and Eu³⁺-doped Gd₂O₃ hexagram-like microcrystals, inheriting the Gd(OH)₃ precursors' morphology, were obtained during a direct annealing process in air. The corresponding Gd₂O₃:Eu³⁺ hexagram-like microcrystals exhibit strong red emission pertaining to the ⁵D₀→⁷F₂ transition of the Eu³⁺ ions under UV light, which have potential applications in novel optoelectronic devices.     

Electrical properties of (Bi2O3)0.75(RE2O3)0.25 ceramics (RE=Dy, Y, Ho, Er and Yb)

Five kinds of rare earth stabilized bismuth oxide ceramics, (Bi₂O₃)_0.75(RE₂O₃)_0.25 (RE=Dy, Y, Ho, Er and Yb), were synthesized by sintering a mixture of Bi₂O₃ and RE₂O₃ at 900–1100 °C and their electrical properties were investigated. The bulk density and the lattice constant linearly increased with an increase in the atomic weight of RE and the ionic radius of RE³⁺, respectively. The electrical conductivity at 300 °C slightly increased with the increasing ionic radius of RE³⁺, while at 500 and 700 °C, it was constant regardless of the ionic radius of RE³⁺. The migration activation energy and the association activation energy showed a maximum value and a minimum value at RE=Er, respectively.     

Microwave-induced small size effect of (Ba,Sr)3MgSi2O8:0.06Eu, 0.1Mn phosphor for 660 nm-featured bio-lighting

The 660 nm-featured (Ba, Sr) ₃MgSi₂O₈:0.06Eu^{2 +}, 0.1Mn²⁺(AMS-EM) phosphor in violet for red/blue bio-lighting LEDs was prepared by 2.45 GHz microwave (MW) high temperature firing procedure. The phase-pure host phase, (Ba, Sr) ₃MgSi₂O₈, was formed to be responsible for simultaneous red band emission from Mn ion and blue band emission from Eu ion, while the formation of an impurity phase of Sr₂SiO₄ responsible for 505 nm-peaked green band emission for Eu ion was effectively suppressed owing to MW fast-heating procedure. Small sized and agglomeration-free phosphor particles were either observed, which was probably resulted from suppressing the grain growth in as-formed host particles, compared with conventional high-temp solid state (SS) reaction firing procedure. These results indicate that high-temp MW firing procedure is suitable for preparing this simultaneously red- and blue-emitting AMS-EM phosphor in the application of bio-lighting for plant cultivation.     

Fabrication and properties of highly transparent Tm3Al5O12 (TmAG) ceramics

Highly transparent Tm₃Al₅O₁₂ (TmAG) ceramics were fabricated by solid-state reaction and vacuum sintering. Densification, microstructure evolution, mechanical, thermal, and optical properties of the TmAG ceramics were investigated. Fully dense TmAG ceramic with average grain size of 15 μm was obtained by sintering at 1780 °C for 20 h. The in-line transmittance was 80.5% at 2000 nm. The absorption coefficients at 682 nm and 785 nm were 8.03 cm⁻¹ and 8.33 cm⁻¹, respectively. The Vickers hardness, the Young modulus, the bending strength, and the fracture toughness values were 15.14 GPa, 343 GPa, 230 MPa, and 2.35 MPa m^1/2, respectively. The thermal conductivity at room temperature was 3.3 W/m K and the average linear thermal expansion coefficient from 20 °C to 1000 °C was 8.915 × 10⁻⁶ K.     

Effect of strontium and phosphorus source on the structure,morphology and luminescence of Sr5(PO4)2SiO4:Euphosphor prepared by solid-state reaction

Sr₅(PO₄)₂SiO₄:Eu²⁺ phosphosilicate phosphor was prepared by high temperature solid-state reaction. Effects of strontium sources (strontium oxide, strontium nitrate and strontium carbonate) and of phosphorus sources (diammonium phosphate, strontium monophosphate) on the reactivity of their mixture during heating and on phase composition, morphology and photoluminescence excitation and emission properties of the phosphors were investigated by TG–DTG–DSC, XRD, SEM and photoluminescence spectroscopy. The sequence of the solid-state reactions when using the different starting reagents was discussed based on the TG–DTG–DSC results. It was found that it is hard to prepare pure Sr₅(PO₄)₂SiO₄:Eu²⁺ phosphor with either of strontium sources studied when stoichiometric (NH₄)₂HPO₄ was used as a phosphorus source. Minor Sr₂SiO₄ impurity phase was present in the phosphors. The content of impurity phase, the morphology and resultant photoluminescence properties of the phosphors were markedly influenced by the strontium source employed. When SrCO₃ was used as the strontium source, the phase purity of the phosphor was improved with the addition of excess (NH₄)₂HPO₄. When (NH₄)₂HPO₄with 5% excess or SrHPO₄ in stoichiometric ratio was used as the phosphorus source a pure phase phosphor was obtained. In addition, the morphology and photoluminescence of the phosphor were also influenced by phosphorus source. The possible reasons causing different properties of the phosphors prepared using different raw materials were discussed based on reaction schemes.     

Synthesis,crystal structure and temperature dependent luminescence of Eu3+ doped SrGd2O4 host: An approach towards tunable red emissions for display applications

In the present paper, an investigation on the structural and photoluminescence (PL) properties of SrGd₂O₄:Eu³⁺ ceramic phosphors synthesized by homogeneous precipitation method followed by combustion process has been reported. The samples, annealed at 1200 °C, were crystallized into orthorhombic phase without any impurities. Microscopic studies revealed the irregular morphology of the obtained ceramic phosphor particles having sizes in the range of 0.3–3 µm. The characteristic photoluminescence properties and decay curves were studied in detail as a function of Eu³⁺ concentration and temperature. The Eu³⁺ doped ceramic samples illuminated with UV light revealed the characteristic red luminescence corresponding to ⁵D₀→⁷F_J transitions of Eu³⁺. The concentration quenching phenomenon of Eu³⁺ ions in the present host, analyzed in the light of ion-ion interaction, indicated multipolar interaction between Eu³⁺ ions. Finally, the intensity parameters (Ω₂, Ω₄) and various radiative properties such as stimulated emission cross-section (σ_e), gain band-width (σ_e×Δλ_eff) and optical gain (σ_e×τ_exp) of Eu³⁺ in the SrGd₂O₄ ceramic phosphors have been calculated by using Judd-Ofelt theory. The present phosphor system exhibited efficient red emission with high red color purity (95%) and adequate thermal stability even at 200 °C. Present research broadly indicated the suitability of SrGd₂O₄:Eu³⁺ ceramic phosphor for display applications.     

A reddish orange stoichiometric phosphor LiEu(PO3)4 for white light-emitting diodes

Stoichiometric phosphors LiGd_1−xEu_x(PO₃)₄(x=0, 0.2, 0.4, 0.6, 0.8, 1.0) were synthesized via traditional solid state reactions. The X-ray powder diffraction measurements show that all prepared samples are isostructural with LiNd(PO₃)₄. Eu³⁺ doped phosphors can emit intense reddish orange light under the excitation of near ultraviolet light from 370 to 410 nm. The strongest two at 591 and 613 nm can be attributed to the transitions from excited state ⁵D₀ to ground states ⁷F₁ and ⁷F₂, respectively. The typical chromaticity coordinates (x=0.620, y=0.368) of Eu³⁺ doped phosphors are in red area. The recorded absorbance spectra indicate that there is effective absorbance in the near UV region for all Eu³⁺ doped samples. Present research indicates that LiGd_1–xEu_x(PO₃)₄ is a promising phosphor for white light-emitting diodes.     

Color tunable nanocrystalline SrGd2Al2O7:Tb3+ phosphor for solid state lighting

Color tunable Tb³⁺ doped SrGd₂Al₂O₇ nanophosphor is synthesized employing a facile and economic urea assisted solution combustion approach. XRD studies confirm the crystallization of single phased SrGd_2(1-x)Tb_2xAl₂O₇ nanophosphor in tetragonal lattice with I4/mmm (139) space group. Rietveld refinement is performed over SrGd_1.9Tb_0.1Al₂O₇ sample to execute qualitative as well as quantitative phase analysis. TEM analysis confirms the more or less spherical shaped phosphors in nano domain with average particle size ranging 45–80?nm. Photoluminescent investigation reveals that this nanophosphor can be successfully excited by ultraviolet light yielding significant luminescent properties arising due to radiative transitions from ⁵D_3,4 levels to ⁷F_j levels. Dipole-dipole interactions are solely responsible for the energy transfer causing concentration quenching. Concentration controlled luminescent tendency can be employed to induce chromaticity from blue to green region. Findings of the study proclaim the application of this nanophosphor as one of the green component of tricolor based ultraviolet excited white LEDs.     

Developing the properties of new blue phosphors: TiO2-doped Zn2SiO4

2ZnO + SiO₂ + X mol% TiO₂ (Zn₂SiO₄-X-TiO₂, 1 ≤ X ≤ 3) and 2ZnO + SiO₂ + 3 mol% MnO₂ (Zn₂SiO₄-3-TiO₂) compositions were prepared using nanoscale ZnO, SiO₂, TiO₂, and MnO₂ particles. The mixing powders were calcined between 1000 °C and 1300 °C in a N₂ atmosphere. Zn₂SiO₄ was the only phase in the calcined Zn₂SiO₄-X-TiO₂ phosphors. We found that the photoluminescence (PL) properties of synthesized Zn₂SiO₄-X-TiO₂ phosphors revealed these to be blue rather than green. The effects of TiO₂ content and calcining temperature on the PL properties of Zn₂SiO₄-X-TiO₂ phosphors were rigorously investigated.