Solid-state Reaction Method Research Articles

Multifunctional Near-Infrared Luminescence Performance of Nd3+ Doped SrSnO3 Phosphor

The phosphors with persistent luminescence in the NIR (near-infrared) region and the NIR-to-NIR Stokes luminescence properties have received considerable attention owing to their inclusive application prospects in the in vivo imaging field. In this paper, Nd3+ doped SrSnO3 phosphors with remarkable NIR emission performance were prepared using a high temperature solid state reaction method; the phase structure, morphology, and luminescence properties were discussed systematically. The SrSnO3 host exhibits broadband NIR emission (800–1300 nm) with absorptions in the near ultraviolet region. Nd3+ ions emerge excellent NIR-to-NIR Stokes luminescence under 808 nm laser excitation, with maximum emission at around ~1068 nm. The concentration-dependent luminescence properties, temperature dependent emission, and the luminescence decay curves of Nd3+ in the SrSnO3 host were also studied. The Nd3+ doped SrSnO3 phosphors exhibit exceptional thermal stability; the integrated emission intensity can retain approximately 66% at 423 K compared to room temperature. Most importantly, NIR persistent luminescence also can be observed for the SrSnO3:Nd3+ samples, which is in the first and second biological windows. A possible mechanism was proposed for the persistent NIR luminescence of Nd3+ based on the thermo-luminescence spectra. Consequently, the exciting results indicate that multifunctional NIR luminescence has been successfully realized in the SrSnO3:Nd3+ phosphors.

Antithermal-Quenching Near-Infrared Emitting Lu2SrAl4SiO12:Cr3+ Garnet-Type Phosphor for High-Resolution Nonvisual Imaging.

Near-infrared (NIR) light allows fast and nondestructive detection with deep penetration into biological tissues and is widely used in food inspection, biomedical imaging, night vision security, and other fields. Cr3+-doped NIR first region (NIR-I) phosphors have many interesting features that have attracted a lot of attention recently. However, practical issues, such as low photoluminescence quantum efficiency and poor thermal stability, need to be addressed. We synthesized Cr3+-doped Lu2SrAl4SiO12 garnet-type phosphors using a high-temperature solid-state reaction method. Under blue-light (@ 430 nm) excitation, the phosphors exhibited broadband NIR-I emission in the range of 600-1000 nm, with an emission peak at 710 nm. This system is unique, as the emission had multipeak sharp-line superposition and the Cr3+ ions were situated in a relatively strong crystal field environment, as opposed to a weak crystal field environment for other matrix. The optimal doping content of Cr3+ ions was 2 mol %, and its internal quantum efficiency was ∼76.8%. Surprisingly, this NIR phosphor showed an antithermal quenching effect, and the integrated luminescence intensity of NIR-I emission measured at 573 K was 206.3% of that measured at 303 K. We found that the antithermal quenching of NIR-I luminescence was caused by the extremely low thermal expansion coefficient and rigid structure of the Lu2SrAl4SiO12 matrix in the temperature range, as well as the weakening of electron-phonon coupling with increasing temperature. The optimized phosphor was packaged with a blue chip into a NIR phosphor-converted light-emitting diode device. The light source device showed an output power of 119.02 mW and an electro-optical conversion efficiency of 11.02% under a driving current of 300 mA. The application potential of this NIR phosphor was demonstrated in the field of high-resolution nondestructive imaging.

Syntheses, structures and characterization of noncentrosymmetric MZnPO4 (M = K, NH4).

Two phosphates, KZnPO4 and NH4ZnPO4, were successfully synthesized using a solid-state reaction method and characterized via single-crystal X-ray diffraction. Both of their structures feature a three-way skeleton composed of isolated PO4 and ZnO4 tetrahedra, with K+/NH4+ cations occupying the spaces within the frameworks to balance charges. These compounds are isostructural and crystallize in the noncentrosymmetric P63 space group. Their structures were compared, revealing that non-centrosymmetric (NCS) KZnPO4 and NH4ZnPO4 exhibit second harmonic generation (SHG) responses of 0.4 × KDP and 1 × KDP, respectively. Furthermore, by combining the electronic structure and SHG density calculations, we examined the effects of ZnO4 tetrahedra on the SHG response of KZnPO4 and NH4ZnPO4.

Effect of anisotropy field on the resonance frequency and reflection loss shift characteristics of barium hexaferrite ceramics

Abstract For this study, a modified barium hexaferrite based microwave and radar absorbing material was used. Synthesis and characterization of BaFe(12-2x)(MnTi)xO19 (0.1 ≤ x ≤ 1.0) have been prepared by solid state reaction method. The X-ray diffraction patterns reveal that all samples only crystallized into M-type barium hexaferrite after calcination at 1200 °C. Surface morphology images show that the hexagonal flake-like particle is formed at the initial stages of the Mn-Ti substitution level. The magnetic properties measurement reveals that the variation of magnetization values may vary based on preferable site occupation of Mn4+-Ti2+ cations to replace Fe3+ cations. The significant decrease in field coercivity (Hc) from 3.18 kOe to 0.51 kOe with the increase of Mn-Ti substitution affected the lowering values of field anisotropy (Ha). The maximum reflection loss (RL) positions of BaFe(12-2x)(MnTi)xO19 compositional series are shifted to lower frequency range following the Ha trendlines. The maximum RL value equals to 98.42% microwave absorption at 10.5 GHz has been obtained in x = 1.0 (BaFe10Mn0.5Ti0.5O19) composition.

Theoretical and experimental investigation of BaY2(MoO4)4:xSm3+ phosphors

In this paper, the novel BaY2(MoO4)4:xSm3+ phosphors with strong red emission and high thermal stabilization were prepared by a conventional method of high temperature solid state reaction in air atmosphere. Morphology, phase purity, element distribution, UV–Vis–NIR diffuse reflectance spectroscopy (DRS), and luminescence properties were investigated in detail. The crystal structure of the BaY2(MoO4)4 host was refined with the aid of the Rietveld refinement method by the GSAS program. The electronic band structure and phonon dispersion were performed using plane-wave density functional theory (DFT). The prepared BaY2(MoO4)4:Sm3+ phosphor exhibits excellent red emission under near-ultraviolet excitation. Strong red emission intensity and high thermal stability suggest potential application in backlighting or phosphor-covered white light-emitting diodes (pc-LEDs).

Exploration of bismuth based perovskite materials for organic dyes removal from waste water

The scourge of water pollution due to organic matter is a well-known fact. In order to address this issue, we employed a highly facile method of solid state reaction for the synthesis of bismuth potassium titanate, Bi0.5K0.5TiO3 (BKT) photocatalyst. Furthermore, the bandgap tailoring of the BKT is performed by photo-reduction of Ag onto the BKT, which results in the formation of hetero-structure junctions at the surface of the BKT. The as-prepared BKT and BKT-Ag photocatalysts are systematically characterized by x-ray diffraction, scanning electron microscopy, and high resolution transmission electron spectroscopy. Furthermore, the photocatalyst activity of the BKT and BKT-Ag was analyzed against the target organic pollutants by using UV–Vis spectroscopy. Three organic dyes such as methylene blue, eriochrome Black T, and methylene orange (MO) were used as target organic pollutants. The anchoring of Ag for the formation of hetero-structure junctions at the surface of BKT rendered it to be an ideal photo-catalyst with a bandgap reduction from 3.37 to 2.08 eV. Therefore, lowering the bandgap resulted in enhanced photocatalytic activity of the BKT-Ag. Among the three target dyes, BKT-Ag showed remarkable photo-degradation of MO and Erb T by degrading ≥90% of MO and Erb T in 120 min at neutral pH values. It is believed that BKT based photocatalysts can provide a unique platform for the removal of organic pollutants from wastewater.

Enhanced Specific Capacitance and Cycling Stability of Li2Cu2(MoO4)3 of NASICON Family of Supercapacitor Applications

AbstractNASICON electrode materials exhibit a broad spectrum of electrochemical potentials, robust ionic conductivity, and structural and thermal stabilities. Using solid state reaction method, Li2Cu2(MoO4)3 was synthesized, a member of NASICON family of compounds based on molybdenum. Various analytical techniques employed to assess structural and morphological properties of synthesized nanomaterial. X‐ray diffraction (XRD) pattern indicated that generated Li2Cu2(MoO4)3 nanomaterial exhibited orthorhombic crystalline structure, with crystallite size of approximately 48 nm. The nanomaterial morphology was evaluated using field emission scanning electron microscopy (FESEM), showing columnar‐ or fiber‐like morphology composed of some conductivity points. The elemental composition of Li2Cu2(MoO4)3 was analyzed by EDAX analysis, confirming the presence of elements lithium, copper, molybdenum, and oxygen. The optical properties and band gap of Li2Cu2(MoO4)3 were analyzed by ultraviolet visible diffuse reflectance spectroscopy (UVDRS). Elemental composition of surface along with electronic states and oxidation states of component present in the nanomaterial Li2Cu2(MoO4)3 were investigated from X‐ray photoelectron spectroscopy (XPS). Electrochemical evaluation using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopic (EIS) showed a specific capacitance of 250 F g−1 at 3.5 A g−1 with the high retention rate of 95.82% after 3000 cycles, indicating its potential for high performance supercapacitors.

Performance study of solid electrolyte Ce0.80Gd0.04Sm0.04Er0.04Y0.04RE0.04O2-δ (RE= Yb, Dy, Eu, Nd, Pr, La)

The production of highly conductive electrolytes has been a crucial factor in the practical development of Solid Oxide Fuel Cells (SOFCs). This study highlights the impact of different dopants on the crystal structure, microstructure, and ionic conductivity of a ceria-based matrix within the Ce0.80Gd0.04Sm0.04Er0.04Y0.04RE0.04O2-δ system. The Ce0.80Gd0.04Sm0.04Er0.04Y0.04RE0.04O2-δ (RE = Yb, Dy, Eu, Nd, Pr, La) powders were prepared using the solid-state reaction method. The phase structure, microstructure, and ionic conductivity of the GSEYRE series electrolytes were analyzed using XRD, SEM, EDS, TEM, XPS, AC impedance spectroscopy, and thermal expansion analysis. Phase structure analysis confirmed that all multi-doped electrolytes possessed a cubic fluorite structure with the Fm3m space group. After sintering at 1400°C for 10 hours, all samples exhibited densities exceeding 94%. XPS analysis revealed a high concentration of oxygen vacancies in the GSEYRE. Electrical performance analysis showed that the Ce0.80Gd0.04Sm0.04Er0.04Y0.04Dy0.04O2-δ (GSEYD) electrolyte demonstrated the highest ionic conductivity (σt = 3.36×10-2 S/cm) and the lowest activation energy (Ea = 0.78 eV) at 800°C. The thermal expansion coefficient of the developed electrolytes matched well with commonly used electrode materials. These characteristics make GSEYD a promising candidate for use as an electrolyte material in SOFCs.

Effects of Zn2+/Si4+ co-doping on the cation distribution, crystal structure, and microwave dielectric characteristics of spinel-structured MgAl2O4 ceramics

Investigating the relationship between the structure and dielectric properties of cation-mixed spinel ceramics is crucial for overcoming the limitations of conventional microwave materials. In this study, MgAl2-x(Zn0.5Si0.5)xO4 (x = 0, 0.02, 0.04, 0.06, and 0.08) ceramics were prepared by a solid-state reaction method. The co-substitution for Al with Zn2+/Si4+ induces Al3+ cations for preferential occupation of the 8a site in the oxygen tetrahedra, forming a solid-solution ceramic at x ≤ 0.06. Enhanced ionic diffusion and compressive stress contribute to a dense microstructure (ρ > 95%) with uniform grain-size distribution after heating at 1650 °C for 4 h. Raman and 27Al NMR spectra reveal a relationship between cation distribution and covalency, consistent with the results of Rietveld refinement. The increases in cation disorder and degree of inversion are accompanied by an enhanced covalency of the Al–O bonds, which reduces intrinsic dielectric loss. In addition, the combination of Shannon ion polarizability and bond valence theory suggests that the increases in permittivity (εr) and the temperature coefficient of resonant frequency (τf) are related to the high polarizability of the dopant ions and the abnormal polarizability derived from the decreasing bond valence of the Al2–O site. The sample at x = 0.06 exhibits a low εr of 8.31, high Q × f of 194,159 GHz (at ∼11.35 GHz), and τf of -30.8 ppm/°C, indicating superior microwave application prospects as compared with traditional Mg-Al spinel ceramics.

Evaluation of Luminescent and Thermal Properties of Dy³⁺ Doped Tungstate Phosphors for Optoelectronic and Thermometry Applications

Novel Ca2MgWO6: xDy3+ (x = 1, 2, 3, 4, and 6 mol%) phosphors were synthesized via solid-state reaction method. The phosphor structure remained unchanged upon doping with Dy3+ ions. Phosphors were optical optimizated using 4F9/2 → 6H13/2 transition, and 3 mol% of Dy3+ was found to be optimal concentration. We investigated optical quenching mechanisms including energy transfer, cross-relaxation, charge compensation, and multipole-multipole interactions. Colorimetric analyses assessed colour coordinates, purity, and correlated colour temperature (CCT). The optimized phosphor showed a direct band gap of 3.68 eV, a refractive index of 2.24, and covalent bonding between Dy3+ and the host. It exhibited exceptional thermal stability with only 0.31 wt% loss up to 440°C. Temperature-dependent emission spectra indicated high optical quenching temperature (498.82 K) and activation energy (0.21 eV). A multi-transition ratiometric approach confirmed suitability for non-contact thermometry and LED applications.

Temperature Dependent Photoluminescence Properties of a Y2Ge2O7:Tb3+ phosphors. A dual band ratiometric luminescent thermometer

A series of green light emitting Y2Ge2O7:xTb3+ phosphors (x = 0.2, 0.5, 1.0, 2.0 and 4.0mol%) were obtained via the solid-state reaction method. The single phase was confirmed by XRD technique. The photoluminescence (PL) excitation spectrum, emission spectra at room and as a function of temperature, decay curves of phosphors were studied in detail. The emission spectra show typical emissions of Tb3+ ions, whose relative intensities change with the ion concentration or UV excitation. A shift of the CIE chromaticity coordinates from blueish to green region was observed. The emission decay curves are compatible with a single type of Tb3+ activator. The obtained internal Quantum Yield (iQY) increase with the terbium concentration, up to 10.0% for sample with 4.0mol%. In addition, the relative sensitivity values (Sr) for samples with 1.0 and 2.0mol% reached 0.97 and 2.02%K-1, respectively. These high thermal sensitivities obtained, in comparison with other Tb3+ based optical temperature sensors, in biophysical temperature range (30–45 °C), illustrates the potential use of Y2Ge2O7:xTb3+ phosphors in the design of efficient FIR luminescent thermometers for biological systems or other industrial applications.

Electrical properties and redox stability of series novel high-entropy Bi2VO5.5-based oxides

Exceptional high ionic conductivities have been well documented in the Bi2VO5.5-based materials. However, the poor phase and redox stabilities under a reducing atmosphere hindered their wide applications. Herein, with the aim to improve the phase and redox stabilities under a reducing atmosphere, a high-entropy strategy of multiple-metal-doping was applied to prepare series Bi2V1–4x(GaSiTaZr)xO5.5-δ (0 ≤ x ≤ 0.1) materials by a traditional solid state reaction method. The results revealed that multiple-metal-doping could stabilize the tetragonal phase of Bi2VO5.5 to room temperature and shown good phase and structural stabilities under inert or high oxygen partial pressure atmospheres, as well as pure oxide ion conduction which was about two orders of magnitude higher than that of the parent material, e.g. ∼2.0×10−2 S/cm at 400 ºC for the x = 0.05 sample while ∼1.5×10−4 S/cm for the x = 0 sample. Although the Bi2V1–4x(CuNiNbTi)xO5.5-δ materials would still be readily reduced under a reducing environment and introduce strong electronic conduction, the phase stability was apparently improved. Thus, improving the redox stability and suppressing the electronic conduction of the stabilized Bi2VO5.5-based materials under a reducing atmosphere is still the direction we should strive for.

Multicolor luminescence and high efficient optical thermometric performance of Eu3+ and Sm3+ in self-activated Na2LuMg2V3O12 garnet

To develop efficient luminescence and optical thermometry materials for color display and non-contact temperature measurement, novel RE3+ (RE = Eu, Sm) doped self-activated Na2LuMg2V3O12 phosphors were prepared by a typical solid-state reaction method. Their crystal structure, morphology, multi-color luminescence and temperature sensing properties were elaborately investigated. Under UV light excitation, an intense and broad green-yellow emission band from VO43– group is observed in the Na2LuMg2V3O12 matrix, indicating its potential application in solid state lighting. After the incorporation of Eu3+ and Sm3+ ions, efficient energy transfer (ET) from VO43– group to Eu3+/Sm3+ ions occurs and the emission color of the samples can be readily tuned among different color ranges. Besides, based on the change of luminescence intensity and lifetimes of VO43– group in Na2LuMg2V3O12:Eu3+ and Na2LuMg2V3O12:Sm3+, the ET efficiency was analyzed and the mechanism is illustrated. Finally, large discrepancy between the thermal stability of VO43– group and Eu3+/Sm3+ ions are observed in the temperature-dependent emission spectra of Na2LuMg2V3O12:Eu3+ and Na2LuMg2V3O12:Sm3+. By taking advantage of the luminescence intensity ratio (LIR) between VO43– group and Eu3+/Sm3+ ions in Na2LuMg2V3O12:0.01Eu3+ and Na2LuMg2V3O12:0.07Sm3+, two new types of optical thermometry mediums were designed and their basic temperature sensing parameters were calculated.

Violet Light Excitable BaLiZn3(PO4)3: Eu3+ Orange-red-emitting Phosphor towards White LED Application

White light-emitting diode (WLED) has been widely used as solid-state lighting in recent years, with the advantages of energy saving, high luminous efficiency, and safety. Red phosphors are crucial to the color rendering index of WLED, and Eu3+-activated red phosphors can significantly improve the chromaticity performance of WLED. In this work, a series of new orange-red emitting BaLiZn3(PO4)3: Eu3+ phosphors were synthesized through high-temperature solid-state reaction method. The phase composition, crystal structure, morphology and photoluminescence properties of BaLiZn3(PO4)3: Eu3+ samples were investigated. The phosphors can be effectively excited by the violet light at 394 nm and emit orange-red lights corresponding to the electric dipole transition (5D0→7F1) at 594 nm. The optimal doping concentration of Eu3+ ions was about 5 mol%. The concentration quenching was caused by the electric dipole-dipole interaction between Eu3+ ions. Temperature-dependent PL spectra indicate that BaLiZn3(PO4)3: Eu3+ has excellent emission and color stability at high temperatures. The color coordinates were calculated and fall in the orange-red luminescent area. The color purity is about 98.3%, and the correlated color temperature is 1710K. These results indicate that the new orange-red phosphor BaLiZn3(PO4)3: Eu3+ has potential application prospects in WLED.

Microwave Absorption and Magnetic Properties of M-Type Hexagonal Ferrite Ba0.95Ca0.05Fe12-xCoxO19 (0 ≤ X ≤ 0.4) at 1-18 GHz.

In order to improve the microwave-absorption performance of barium ferrite and broaden its microwave-absorption band, BaFe12O19, Ba0.95Ca0.05Fe12O19, and Ba0.95Ca0.05Fe12-xCoxO19 (x = 0.1, 0.2, 0.3 and 0.4, respectively) hexaferrites were synthesized by the solid-state reaction method, and the influence of Co ion substitution on the phase composition, microstructure, magnetic properties, and microwave-absorption ability of the ferrites in this system was studied. Introducing minor Co ions (x < 0.2) facilitated sintering and grain growth. At x ≥ 0.2, XRD revealed the emergence of the Co2X phase alongside the BaM phase. Increasing Co ion concentration and the secondary X-phase led to slight reductions in saturation magnetization (69 to 63.5 emu/g) and substantial decline in coercivity (2107.02 to 111.21 Oe), attributed to grain size growth and Co2X's soft magnetic nature. Notably, Co2X incorporation significantly enhanced the microwave absorption and provided a tunable absorption band from the Ku to the C band. For a sample with a thickness of 2.0 mm and a doping level of x = 0.2, a minimum reflection loss of -59.5 dB was achieved at 8.92 GHz, with an effective absorption bandwidth of 3.31 GHz (7.07-10.38 GHz). The simple preparation method and good performance make Ba0.95Ca0.05Fe12-xCoxO19 (x = 0.1, 0.2, 0.3 and 0.4, respectively) hexaferrites promising microwave-absorbing materials.

STUDYING THE ELECTROCHEMICAL PROPERTIES OF POTASSIUM-DOPED SODIUM-MANGANESE OXIDE CATHODE MATERIALS FOR SODIUM-ION BATTERIES

The development of layered sodium manganese oxide cathode materials with high capacity and long life is one of the keys to boosting the performance of sodium-ion batteries (SIBs), but it remains a great challenge. In this work, a potassium doped P2-type sodium manganese oxide, Na0.8K0.1Mn0.9O2 (NKMO), is developed as a high-capacity and long-lasting cathode for high-performance SIBs. Sodium-potassium-manganese oxide Na0.8K0.1Mn0.9O2 was synthesized by a conventional solid-state reaction method. Crystal structure and morphology of the NKMO material were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The NKMO material was utilized to fabricate CR2032-type coin cells, and later evaluated for its electrochemical characteristics. The electrochemical characteristics of NKMO were evaluated through cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charging-discharging (GCD) at different current densities on a NEWARE battery testing system. The NKMO material had a superior initial charge and discharge capacity, approximately 130 mAh.g-1 and 125 mAh.g-1, respectively, within the voltage range of 1.5-4 V at a current density of 0.1 C. Remarkably, the capacity remained stable at 100 mAh.g-1 even after 100 cycles. These findings indicate that NKMO is a highly promising cathode material for sodium-ion batteries.

Study of the Activator Effects on the Specific Surface Area of Porous Carbon and its Performance as Lithium-Sulfur Battery Cathode

A study was conducted to investigate the effect of activator types KOH, ZnCl2, and H3PO4 on the specific surface area of porous carbon and its performance as a Li-S battery. Porous carbon was synthesized from candlenut shells through a carbonization process at 700 °C using three types of activator solutions with a concentration of 0.36 M. The porous carbon activated with KOH achieved the best results, with a specific surface area of 681 m²g-1. The porous carbon candlenut shell-sulfur (PCCS-S) composite was obtained by the solid-state reaction method in a ratio of 1:2.5 w% and heat-treated at 155 °C to form the PCCS-S composite. The PCCS-S composite was then made into a slurry and coated onto Al-foil to obtain a layer of electrodes with a thickness of 200 µm. The PCCS-S cathode was then assembled into a coin battery with lithium metal as the anode and an electrolyte of 1.0 M LiTFSi solution dissolved in 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) (v/v, 1:1). Charge-discharge characterization was carried out at a charge rate of 1 C for 50 cycles. Characterization shows that the performance of the PCCS-S KOH composite cathode Li-S battery is stable at a specific capacity of 324 mAhg-1 after the first 10 cycles, with an average Coulombic efficiency of around 86.8 %.

Impedance Spectroscopy of Lanthanum-Doped (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 Ceramics

This study examines the effects of La3+ doping on (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3(PBZT) ceramics, which were synthesized using the conventional solid-state reaction method. X-ray diffraction analysis confirmed that the PBZT structure, including PBZT doped with La3+ at concentrations x = 1 at.% and x = 2 at.%, exhibited a rhombohedral (R3c) space group, while higher doping levels of x = 3 at.% and x = 4 at.% led to a dominant cubic (Pm-3m) phase with approximately 30% of a remnant rhombohedral component. Scanning electron microscopy (SEM, JEOL JSM-7100F TTL LV, Jeol Ltd., Tokyo, Japan) and energy dispersive X-ray spectroscopy (EDS) were utilized to investigate the structure and morphology of these ceramics. The findings indicated that the chemical composition of the ceramic samples closely corresponded to the initial stoichiometry of the ceramic powder. An increase in the amount of lanthanum results in a decrease in the average grain size of the ceramics. The electrical properties were further evaluated using complex impedance spectroscopy (IS) over a range of temperatures and frequencies, as well as temperature dependence of DC conductivity. The similarity in the changes in activation energy for DC conductivity and grain boundary conductivity, caused by lanthanum ion modification, allows for the conclusion that grain boundaries are the primary microstructural element responsible for conductivity in these materials.

The Impact of the Final Sintering Temperature on the Microstructure and Dielectric Properties of Ba0.75Ca0.25TiO3 Perovskite Ceramics.

Ba0.75Ca0.25TiO3 ceramics were successfully synthesized by a simple solid-state reaction method. This study examined the influence of sintering temperature on the structure, microstructure, dielectric properties and electrical behavior of the material. The XRD analysis reveals that the tetragonal phase (P4mm) is dominant in all the synthesized materials, with those sintered at T = 1400 °C and T = 1450 °C being single-phase, while others exhibit a minor orthorhombic phase (Pbnm). Higher sintering temperatures promoted better grain boundary formation and larger grain sizes. The electric permittivity increased with temperature up to T = 1400 °C, followed by a sharp decline at T = 1450 °C. Additionally, the Curie temperature decreased with increasing sintering temperature, indicating changes in phase transition characteristics. Thermal analysis showed that higher sintering temperatures led to sharper heat capacity peaks, while pyroelectric and thermally stimulated depolarization currents were maximized at T = 1400 °C due to oxygen vacancies. These findings highlight the significant impact of sintering temperature on the material's structural and functional properties.

Cr3+-Doped LiAlO2 NIR-I Emitting Phosphors with Superior Resistance to Thermal Quenching for Night Vision Monitoring and Bioimaging.

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) as a new NIR light source has outstanding application potential in the fields of NIR spectroscopy analysis, sensing, imaging, and pattern recognition. Therefore, the development of NIR phosphors with good NIR luminescence thermal stability has attracted much attention. To this end, we developed LiAlO2:Cr3+ garnet-type NIR phosphors by a high-temperature solid-state reaction method. Under 405 nm excitation, the Cr3+ ions located in tetrahedrons of LiAlO2 emit NIR emission in a broadband NIR emission that covers 650-900 nm mixed with several sharp narrowband R-line emissions, which showed excellent luminescence thermal stability with integrated intensity of emission measured at 573 K is ∼90.86% of that measured at 303 K caused by good structural rigidity and low thermal expansion coefficient of the matrix material. An NIR pc-LED device assembled with the optimized LiAlO2:Cr3+ and a commercially available purple LED chip emitted NIR output power of ∼98.172 mW at a driving current of 300 mA and demonstrated an electro-optical conversion efficiency of ∼9.09%, while demonstrated it has excellent application potential in the fields of night vision monitoring and biomedical imaging.