Luminescence and electrical properties of Eu-modified Bi0.5Na0.5TiO3 multifunctional ceramics

The Eu³⁺-modified Bi_0.5Na_0.5TiO₃ (BNT) ceramics have been fabricated by the solid-state reaction method. The impact of Eu³⁺ doping on the structure, photoluminescence, and electrical properties has been studied by XRD, SEM, PL spectra, and LCR meter. X-ray diffraction analysis reveals that the crystal structure of the samples is well matched with the trigonal perovskite, and the optimal temperature of presintering is 880°C. The Eu³⁺-doped BNT ceramics show excellent red fluorescence at 614 nm corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ under 466 nm excitation and relatively long fluorescence lifetime. The BNT-0.02Eu ceramic density is up to 5.68 g/cm³ and the relative density is up to 94.6% with sintering temperature 1075°C. The piezoelectric constant (d₃₃) of samples has been significantly improved up to 110 pC/N by Eu³⁺ doping. The BNT-0.03Eu ceramic presintered at 880°C and sintered at 1050°C has good dielectric properties and excellent luminescence properties. Eu³⁺-doped BNT ceramics make it potential applications for novel integrated electro-optical and multifunctional devices.     

Low-temperature solid-state synthesis and luminescent performance of a novel Li2NaBP2O8-based phosphor activated with europium (III)

For the application of inorganic phosphors in solid-state lighting field, exploring a synthesis route with low energy consumption and low cost is the current research focus. In this study, a low-temperature solid-state synthesis route for a novel Li₂NaBP₂O₈:Eu³⁺ (LNBP:Eu) phosphor is reported. The phase structure, morphology, and elemental composition of its powder phase are characterized. According to photoluminescence and X-ray photoelectron spectroscopy data, the occupancy site and oxidation state of doping europium are discussed. Under near-UV (395 nm) excitation, the powder phase exhibits reddish-orange emission with a dominant ⁵D₀ → ⁷F₁ transition of europium. The intensity of visible photoluminescence is closely influenced by the europium doping content. The optimal content is 0.04 mol, and concentration quenching is ascribed to energy transfer among the nearest-neighbor europium ions. Moreover, chromatic properties are investigated in detail. The obtained data show that the LNBP:Eu powder phase is a prospective phosphor for application in near-UV-converted warm white light-emitting diodes.     

Eu2+ activated novel eulytite Na3Bi5(PO4)6: Eu3+ phosphors: Enhanced luminescence and thermal stability for photonics application

For the first time, novel eulytite-like Eu²⁺/Eu³⁺: Na₃Bi₅(PO₄)₆ phosphor was synthesized via high temperature solid-state reaction method in reduction environment, and the structure, luminescence performances and thermal stability were investigated and discussed using various techniques. X-ray refinement diffraction and Raman spectra revealed the around 200 nm well-crystallized eulytite-type (I43d space group) phosphors were synthesized, and a diagram of crystal structure of Na₃Bi₅(PO₄)₆ was proposed. X-ray photoelectron spectroscopy analysis confirmed the co-existence of Eu²⁺ and Eu³⁺ ions which exhibited characteristic 4f⁶5d→⁸S_7/2 transition of Eu²⁺ and ⁷F₀→⁵D_0,1,2,3,4 transitions of Eu³⁺ ions. On the other hand, due to the activation of Eu²⁺, samples displayed good tunability on excited and emission behaviors under different excited laser. The JO parameters, emission cross-section, branching ratio and asymmetric ratio indicated that the Eu doping increased the covalency and asymmetry of host. Thermal quenching was studied and the reasons were discussed. Through the comparison of phosphors prepared in different conditions, the thermal stability& repeatability, radiative lifetime, color purity and activation energy were remarkably superior due to the Eu doping and in particularly Eu²⁺ activation. Finally, the energy level and CIE chromaticity diagrams were plotted to explain the mechanism of Eu²⁺ activation and energy transfer between Eu²⁺ and Eu³⁺ ions. The 0.5%Eu doped Na₃Bi₅(PO₄)₆ exhibited promising tunable red-emission performance with quantum efficiency of 92%, activation energy of 0.24 eV, red color purity of 93.74% and very low non-radiative transfer ratio 44.20 s^?1 with smaller CCT (<2200 K).     

Effect of the Eu3+ Addition on Photoluminescence and Microstructure of ZnO–CdO–TeO2 Glasses

In this work, the role of europium doping of glasses formulated in the ternary system ZnO–CdO–TeO₂ is described. The Eu‐doped oxide glasses were prepared by the conventional melt‐quenching method and by using three different compositions. Structural studies reveal that there exists a good affinity between Cd and some rare earth (RE) ions to form the crystalline phase. The X‐ray diffraction (XRD) diagrams display that the structure of these glasses is amorphous and with the increase in CdO content and the compatibility of Eu³⁺, there is a tendency to form nanocrystals of CdTe₂O₅. The scanning electron microscopic (SEM) observation of their microstructure confirms the presence of phase separation. Differential thermal analysis (DTA) of these glasses showed small exothermic peaks noted around 450°C for the V2 glass and 480°C for V1 and V3 glasses, which could be attributed to the formation of these crystals. The infrared spectra showed a main absorption band around 800–600 cm^?1 corresponding to the Te–O stretching mode in TeO₄ and TeO₃ groups. By optical absorption (OA), the band gap (E_g) for each glass was determined; these values were 3.27, 3.14, and 3.3 eV for the V1–V3 glasses, respectively. Furthermore, the presence of Eu³⁺ was detected in the 370–470 nm short‐range wavelengths. The photoluminescence (PL) experiments of the glasses showed light emission due to the following transitions: ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂, ⁵D₀ → ⁷F₃, and ⁵D₀ → ⁷F₄.     

Structural and spectral properties of red light emitting Eu3+ activated TiO2 nanophosphor for white LED application

The structural and luminescent properties of Eu³⁺ doped TiO₂ nanophosphors synthesized by low cost combustion method were investigated. The X-ray diffraction analysis revealed that crystallite size decreases with doping concentration. Lattice volume expansion occurred due to the substitution of Ti⁴⁺ ions by larger ionic radii ions Eu³⁺. FESEM images showed prepared phosphors to be nano size spherical shaped particles. Energy band gap of 3 mol% Eu³⁺ doped samples decreased to 3.15 eV due to doping effect. The Eu³⁺ doped TiO₂ nanophosphors exhibited main red emission peak centered at 616 nm under 395 nm UV light excitation. Concentration quenching was observed at 3 mol% doping, that has been ascribed to dipole-dipole interaction. The covalent nature of Eu-O bond and environment around Eu³⁺ ions were discussed using Judd-Ofelt (J-O) intensity parameters. Internal quantum efficiency was calculated using excited state lifetime ⁵D₀ state of Eu³⁺ ion and J-O theory. The CIE colour coordinates and colour purity were calculated using the spectral energy distribution function. Low excited state life time indicated that Eu³⁺ doped TiO₂ can be used as red emitting phosphor for white light emitting diode applications.     

Synthesis of Eu-doped hydroxyapatite whiskers and fabrication of phosphor layer via electrophoretic deposition process

Highly biocompatible and efficiently luminescent whiskers of the hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp) doped with various concentrations (0-5 at.%) of europium were prepared by hydrothermal synthesis and the Eu-doped Hap-coating layers onto the surface of titanium substrate were fabricated by the electrophoretic deposition (EPD) process for fluorescent probe application. The maximum doping concentration of Eu accommodating into the host lattice of HAp was detected as ~1.5 at.% and all the hydrothermally synthesized Eu-doped HAp whiskers were found to have high crystallinity and orientation growth along the c-axis by X-ray diffraction (XRD) identification. The valence of the doped Eu was identified as trivalent and divalent coexistence at a concentration percentage of Eu³⁺: Eu²⁺ = 78%: 22% by X-ray photoelectron spectroscopy (XPS) spectra. The replacement site of the doped Eu ions in the crystal structure of HAp host was clarified by Rietveld refinement. The whisker morphology of the hydrothermally synthesized particle was demonstrated by field-emission scanning electron microscopy (FE-SEM) observation and their component elements were analyzed by energy dispersive X-ray (EDX) mapping. The photoluminescence (PL) emissions of the Eu-doped HAp whiskers and fabricated their coating layers were both revealed mainly at ~615 nm (⁵D₀ → ⁷F₂) and ~697 nm (⁵D₀ → ⁷F₄), which is a wavelength that easily transmitting through living system for biological imaging. The PL emission are falling in the region of reddish orange and belonging to color temperature below 1500 K. Decay time and internal and external quantum efficiencies (QEs) were also measured to reveal them depending on the doping concentration of Eu. The hydrothermally prepared Eu-doped HAp whiskers would be aimed at biomedical application, due to their promising fluorescent function of probe for in vivo imaging in medical diagnose by utilizing the superior biocompatibility of the HAp host and highly efficient luminescent property of the Eu activator.     

Synthesis,structural characterization,and photoluminescence properties of TTB‐type PbTa2O6:Eu3+ phosphor

Undoped and Eu³⁺‐doped tetragonal tungsten bronze (TTB) PbTa₂O₆ phosphors were synthesized by using solid‐state reaction method. Synthesized samples were characterized by XRD, SEM‐EDS, and photoluminescence analyses. XRD results revealed TTB‐type crystal structure with single phase up to 10 mol% Eu³⁺ doping concentration. In SEM‐EDS analyses, elemental composition of Pb decreased with the increasing concentration of Eu³⁺. Emissions at the excitation wavelength of 398.5 nm were observed at 593.2 and 618.8 nm due to ⁵D₀→⁷F₁ transitions and ⁵D₀→⁷F₂ transitions, respectively. Emission increased with the increasing Eu³⁺ doping concentration up to 10 mol% and not observed concentration quenching.     

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).     

Microstructure and photoluminescence of Eu-doped Sr3Al2O6 phosphors calcined with and without H3BO3 flux

The development of highly efficient and stable red phosphors fabricated using cost-effective and simple mass-production methods is essential for applications in future displays and lighting devices. Herein, we investigate the phase formation, microstructures, and luminescence properties of Sr₃Al₂O₆:Eu powders synthesized using a solid-state reaction process. Single-phase Sr₃Al₂O₆:Eu phosphors exhibiting excellent photoluminescence with color-tunable orange-red and red colors under different excitation wavelengths were successfully synthesized. The optimal Eu doping concentration of Sr₃Al₂O₆, yielding strong photoluminescence with phase stability, was 5 at. %, with the concentration quenching point determined by systematic exploration. The addition of H₃BO₃ as a flux significantly affected the grain size and improved the emission intensity of the synthesized (Sr_0.95Eu_0.05)₃Al₂O₆ phosphors up to 12.5 wt %, while secondary phases were formed at higher flux concentrations. The photoluminescence intensities of the ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions of 12.5 wt % H₃BO₃ added (Sr_0.95Eu_0.05)₃Al₂O₆ increased by 3.4 and 4.2 times compared with the flux-free powders under the 394 nm-wavelength excitation, while the decay time decreased from 7.35 to 5.40 ms. Our report of the enhanced photoluminescence intensity and shortened decay time of (Sr_0.95Eu_0.05)₃Al₂O₆ phosphors following the flux addition is promising for production of single-phase phosphors emitting multi-colors, which is needed for optical devices activated by various excitation frequencies.     

Quantitative phase analyses of Eu3+ -doped (Na1-x,Kx)0.5Bi0.5TiO3ferroelectric ceramics near morphotropic phase boundary by photoluminescence spectra

It is widely reported that rare-earth ions could be used to probe the phase structure by photoluminescence (PL) spectra after doping into ferroelectrics, while most reported results are qualitative. In this work, we show that PL spectra of Eu³⁺ ions could be used to do quantitative phase analyses of (Na_1-x,K_x)_0.5Bi_0.497Eu_0.003TiO₃ (NKBT: Eu) ferroelectric ceramics with compositions near morphotropic phase boundary(MPB). The mechanism was elaborated based on the emission intensity ratios of the “hypersensitive” transition to the magnetic dipole transition with the Judd-Ofelt theory. The results were further confirmed by X-Ray Diffraction Rietveld refinements. This work shows a simple yet practical method for quantitative phase analyses for NKBT: Eu ceramics near MPB, and the method is expected to be applied in more ferroelectric material systems.     

Structure and luminescence properties of Eu3+ doped TiO2 nanocrystals and prolate nanospheroids synthesized by the hydrothermal processing

We report on a new approach to the synthesis of Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids. They were synthesized by shape transformation of hydrothermally treated titania nanotubes at different pH and in the presence of Eu³⁺ ions. The use of nanotubes as a precursor to the synthesis of Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids opens the possibility of overcoming the problems related to molecular precursors. The shapes and sizes of the nanotubes, Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids were characterized by transmission electron microscopy (TEM) technique. Crystal structures of the resultant powders were investigated by X-ray diffraction (XRD) analysis. The percentage ratio of Eu³⁺ to Ti⁴⁺ ions in doped nanocrystals was determined using inductively coupled plasma atomic emission spectroscopy. The optical characterization was done by using fluorescence and ultraviolet-visible reflection spectroscopies. An average size of faceted Eu³⁺ doped TiO₂ nanocrystals was 13 nm. The lateral dimensions of Eu³⁺ doped TiO₂ prolate nanospheroids varied from 14 to 20 nm, while the length varied from 40 to 80 nm, depending on precursor concentrations. The XRD patterns revealed the homogeneous anatase crystal phase of Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids independently of the amount of dopant. A postsynthetic treatment (filtration or dialysis) was applied on the dispersions of the doped nanoparticles in order to study the influence of the dopant position on photoluminescence (PL) spectra. In the red spectral region, room temperature PL signals associated with ⁵D₀ → ⁷F_J (J = 1–4) transitions of Eu³⁺ were observed in all samples. The increased contribution of dopants from the interior region of dialyzed nanocrystals to photoluminescence was confirmed by the increase of R value.     

Effects of crystallization and dopant concentration on the emission behavior of TiO2:Eu nanophosphors

Uniform, spherical-shaped TiO₂:Eu nanoparticles with different doping concentrations have been synthesized through controlled hydrolysis of titanium tetrabutoxide under appropriate pH and temperature in the presence of EuCl₃·6H₂O. Through air annealing at 500°C for 2 h, the amorphous, as-grown nanoparticles could be converted to a pure anatase phase. The morphology, structural, and optical properties of the annealed nanostructures were studied using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy [EDS], and UV-Visible diffuse reflectance spectroscopy techniques. Optoelectronic behaviors of the nanostructures were studied using micro-Raman and photoluminescence [PL] spectroscopies at room temperature. EDS results confirmed a systematic increase of Eu content in the as-prepared samples with the increase of nominal europium content in the reaction solution. With the increasing dopant concentration, crystallinity and crystallite size of the titania particles decreased gradually. Incorporation of europium in the titania particles induced a structural deformation and a blueshift of their absorption edge. While the room-temperature PL emission of the as-grown samples is dominated by the ⁵D₀ - ⁷F _j transition of Eu⁺³ ions, the emission intensity reduced drastically after thermal annealing due to outwards segregation of dopant ions.     

Enhanced electrical properties and strong red light‐emitting in Eu3+‐doped Sr1.90Ca0.15Na0.9Nb5O15 ceramics

The luminescent‐ferroelectic materials based on Sr_1.90Ca_0.15Na_0.9Nb₅O₁₅ (SCNN) matrix doping with Eu³⁺ were synthesized by the conventional solid‐state reaction method. The crystal structure, photoluminescence, thermal stability, dielectric, ferroelectric, and piezoelectric behaviors were systematically investigated. XRD results revealed that Eu³⁺ introduction could induce the tungsten bronze phase transition from orthorhombic to tetragonal structures. The dielectric spectra of all specimens showed two broad dielectric anomalies: a high‐temperature ferroelectric phase transition (T_c) and a low‐temperature ferroelastic phase transition (T_s), both of which were suppressed at higher Eu³⁺ concentrations. The enhanced electrical properties were obtained in a proper Eu³⁺ concentration range of 0.03‐0.05. For all SCNN:xEu³⁺ samples, the strong red emission peak at 617 nm originating from the electric dipole transition of ⁵D₀ →⁷F₂ was excited by different light excitations of 395 or 463 nm. Our results demonstrated that Eu³⁺‐doped SCNN materials might have promising potential in advanced multifunctional optoelectronic applications.     

2D‐ and 3D‐Photoluminescence Imaging of Eu(III) Embedded in CeO2 Nanomatrix

2D‐ and 3D‐photoluminescence characteristics of Eu(III) doped in CeO₂ nanoparticles were fully imaged for the first time. Their fundamental natures were also examined by scanning electron microscopy (SEM), X‐ray diffraction (XRD) crystallography, and UV–visible absorption spectroscopy. The magnetic dipole ⁵D₀ → 7F₁ transition was dominated by an indirect transition associated with a O^2?–Ce⁴⁺ charge‐transfer band of CeO₂. The electric dipole ⁵D₀ → ⁷F₂ transition was dominated by a direct transition of Eu(III), indicating that Eu(III) replaces Ce(IV) at octahedral sites (O_h and O) with and without an inversion center. Upon annealing, the photoluminescence intensity caused by direct transition was dramatically decreased, whereas that induced by indirect transition was greatly enhanced. These findings indicate that charge transfer to the Eu(III) at the octahedral (O_h) site with the inversion center is more efficient than that to the Eu(III) site without an inversion center. The absolute quantum yield for the 10 mol% Eu(III)–CeO₂ was found to be ? = 0.007 at an excitation wavelength of 350 nm. The photoluminescence of Tb‐doped CeO₂ was briefly discussed for comparison.     

Enhanced piezoelectric property and promoted depolarization temperature in Fe doped Bi1/2(Na0.8K0.2)1/2TiO3 lead-free ceramics

Piezoelectric sensors and energy harvesters require piezoelectric materials with large piezoelectric responses and good thermal stability. However, a commonly accepted concept is that the promotion of depolarization temperature of Bi_1/2Na_1/2TiO₃-based lead-free ceramics is usually companied by deterioration of piezoelectric properties. In the present study, the effects of acceptor-Fe doping on piezoelectric property and thermal depolarization behavior of Bi_1/2(Na_0.8K_0.2)_1/2TiO₃ ceramics are investigated. Fe doping at an appropriate level (≤ 3.0%) improves piezoelectric property and thermal stability simultaneously, due to the stabilization of long-range ferroelectric order. Piezoelectric constant d₃₃ increases from 125 pC/N to 148 pC/N with Fe amount of 3.0%, and then decreases. The depolarization temperature T_d is promoted continuously with Fe addition, from 76 °C for the undoped sample to 118 °C for the sample with Fe amount of 5.0%. It is proposed that the piezoelectric property and thermal stability can be simultaneously improved by stabilizing the long-range ferroelectric order in Bi_1/2Na_1/2TiO₃-based systems with obvious relaxor character. This work provides a new insight into the improvement of Bi_1/2Na_1/2TiO₃-based lead-free piezoelectric ceramics.     

A single‐phase full‐color emitting phosphor Na3Sc2(PO4)3:Eu2+/Tb3+/Mn2+ with near‐zero thermal quenching and high quantum yield for near‐UV converted warm w‐LEDs

A single‐phase full‐color emitting phosphor Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ has been synthesized by high‐temperature solid‐state method. The crystal structure is measured by X‐ray diffraction. The emission can be tuned from blue to green/red/white through reasonable adjustment of doping ratio among Eu²⁺/Tb³⁺/Mn²⁺ ions. The photoluminescence, energy‐transfer efficiency and concentration quenching mechanisms in Eu²⁺‐Tb³⁺/Eu²⁺‐Mn²⁺ co‐doped samples were studied in detail. All as‐obtained samples show high quantum yield and robust resistance to thermal quenching at evaluated temperature from 30 to 200°C. Notably, the wide‐gamut emission covering the full visible range of Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ gives an outstanding thermal quenching behavior near‐zero thermal quenching at 150°C/less than 20% emission intensity loss at 200°C, and high quantum yield‐66.0% at 150°C/56.9% at 200°C. Moreover, the chromaticity coordinates of Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ keep stable through the whole evaluated temperature range. Finally, near‐UV w‐LED devices were fabricated, the white LED device (CCT = 4740.4 K, Ra = 80.9) indicates that Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ may be a promising candidate for phosphor‐converted near‐UV w‐LEDs.     

Electromechanical Properties of Acceptor‐Doped Lead‐Free Piezoelectric Ceramics

We have studied the processing and electromechanical properties of Mn and Fe‐doped 0.88[Bi_0.5Na_0.5TiO₃]–0.08[Bi_0.5K_0.5TiO₃]–0.04[Bi_0.5Li_0.5TiO₃] piezoelectric ceramics prepared by the mixed oxide route. Different amounts of Mn (0.01, 0.014, 0.015, 0.016, 0.017, 0.02, 0.022) or Fe (0.0125, 0.015, 0.0175) were doped to this lead‐free piezoelectric composition. Ceramics were sintered at different temperatures (1075°C–1150°C) to achieve the highest density and mechanical quality factor. Mn or Fe doping resulted in a considerable enhancement of Q_m in both planar and thickness resonance modes. In 1.5 mol% Mn‐doped ceramics sintered at 1100°C, a planar Q_m of about 970 and tanδ of 0.88% were obtained. In Fe‐doped ceramics, a planar Q_m as high as 900 was achieved. Acceptor dopants also resulted in decreasing the coupling coefficients, the piezoelectric charge coefficient, and the dielectric constant.     

Synthesis,structural characterization,and photoluminescence properties of Eu3+‐doped Mg3‐xEux(BO3)2 phosphor

Eu³⁺‐doped Mg_3‐xEu_x(BO₃)₂ (x = 0.000, 0.005, 0.010, 0.020, 0.050, and 0.100) phosphors were synthesized for the first time by solution combustion synthesis method, which is a fast synthesis method for obtaining nano‐sized borate powders. The optimization of the synthesis conditions of phosphor materials was performed by TG/DTA method. These phosphors were characterized by XRD, FTIR, SEM‐EDX, and photoluminescence, PL analysis. The XRD analysis exhibited that all of the prepared ceramic compounds have been crystallized in orthorhombic structure with space group Pnnm. Also, the influence of europium dopant ions on unit cell parameters of host material was analyzed using Jana2006 program and the crystalline size was determined by Debye‐Scherrer's formula. The luminescence properties of all Eu³⁺‐doped samples were investigated by excitation and emission spectra. The excitation spectra of Mg_3‐xEu_x(BO₃)₂ phosphors show characteristic peak at 420 nm in addition to other characteristic peaks of Eu³⁺ under emission at 613 nm. The emission spectra of Eu³⁺‐doped samples indicated most intensive red emission band dominated at 630 nm belonging to ⁵D₀→⁷F₂ magnetic dipole transition. Furthermore, the optimum or quenching concentration of Eu³⁺ ion has been determined as x = 0.010 showed the maximum emission intensity when it was excited at 394 nm.     

Achieving excellent energy storage properties of Na0.5Bi0.5TiO3 - based ceramics by using a two-step strategy involving phase and polarization modification

Na_0.5Bi_0.5TiO₃-based ceramic specimens have been extensively investigated as ferroelectric materials. After being doped with CaTiO₃, the resulting Na_0.5Bi_0.5TiO₃-based ceramics exhibit relaxor characteristics, and improved energy storage density and efficiency. Based on these above results, CeO₂ was further employed to modify the polarization of the 0.85Na_0.5Bi_0.5TiO₃-0.15CaTiO₃ matrix ceramic to achieve better energy storage performance. The effective energy storage density was enhanced from 1.93 to 2.53 J/cm³ by using the appropriate doping concentration of CeO₂. Grain refinement effect can effectively enhance the electric-field strength from approximately 190 to 230 kV/cm. In particular, when doped with 2% CeO₂, the energy storage efficiency of the sample was maintained at approximately 90% at 30 °C-150 °C and at approximately 80% in the frequency range of 0.2–200 Hz. This combination has very excellent temperature stability and frequency stability, making it a promising candidate for energy storage applications.     

Effects of doping content and crystallite size on luminescence properties of Eu3+ doped fluorapatites obtained from natural waste

In this study, Eu³⁺ doped natural fluorapatites [Ca₁₀(PO₄)₆F₂:xEu³⁺ (x = 0.1, 0.3 and 0.5)] were produced from a natural waste by solid-state powder synthesis, conventional sintering, and spark plasma sintering techniques. The effects of doping content and crystallite size on luminescence properties of fluorapatite were investigated by XRD, SEM, and PL analysis. The obtained results showed that luminescence emission's intensity significantly increased with doping content, but no effect was observed on the density and crystallite size. For the samples produced with different methods, emission intensity was the lowest for sintered samples by SPS (1150 °C, 10 min, 50 MPa) with the smallest crystalline size. In contrast, emission intensity was found much higher for synthesized powders with the largest crystallite size. Furthermore, upon excitation under UV radiation, the Eu doped fluorapatites demonstrated the characteristic ⁵D₀–⁷F₂ and ⁵D₀–⁷F₄ emission lines of Eu³⁺ at 618 nm and 704 nm (red region) with an ultrahigh intensity that has been firstly observed in the literature. Therefore, Eu doped fluorapatites, quickly produced from a natural waste in an eco-friendly and cost-effective way, carry a potential to be used in biological applications and lightning applications.