Conventional Solid-state Reaction Route Research Articles

Sr6Y(PO4)5: Nd3+ a novel whitlockite-type phosphor for optical temperature sensing applications: Synthesis and luminescence properties

Active research in science and technology is improving the development of materials that emit infrared light, with the aim of better optical thermometric sensors. In this paper we report the synthesis of a new NIR-emitting phosphate phosphor, Sr6Y(PO4)5:Nd3+ (SYP: Nd3+), at differing concentrations of Nd3+ using a conventional solid-state reaction route. X-ray diffraction analysis showed that the prepared phosphors exhibit a singular phase with a monoclinic whitlockite structure (space group I2/a). SEM images show micrometer-sized particle. FTIR and Raman spectroscopies confirm the presence of PO43− groups in the examined phosphates. Luminescence features, comprising emission spectra, concentration quenching, and fluorescence lifetime, were investigated for the prepared SYP: Nd3+ samples at various Nd3+ doping concentrations. Excited at 808 nm, the phosphors emitted near-infrared light with four distinct bands corresponding to specific Nd3+ transitions from 4F3/2 to (4I9/2,4I11/2 and 4I13/2) and 4F5/2 to 4I11/2, falling within the first and second biological windows (NIR-I and NIR-II). Importantly, Nd3+ emission characteristics are affected by concentration and temperature. The powders' effectiveness as optical temperature sensors using fluorescence intensity ratio (FIR) between coupled and non-coupled levels was researched across 303–473 K, resulting in two distinctive FIR-based temperature sensor strategies employing emissions at 874.8 nm (4F3/2 → 4I9/2) and 956 nm (4F5/2 → 4I11/2) transitions, all within the first biological window for excitation and emission. Using this method, SYP: Nd3+ revealed a notably elevated sensitivity of approximately 1.16 %K−1 at 303 K, surpassing other Nd3+-doped materials when stimulated within the infrared range. These results strongly suggest the prospective applicability of the analyzed material in monitoring the temperature of biological systems.

Excellent high-temperature dielectric stability of BNT-based ceramics modified by NaNbO3

In this work, (1-x)(K0.5La0.5)0.1Ba0.054(Bi0.5Na0.5)0.846Ti0.95(Cr0.5Ta0.5)0.05O3- xNaNbO3 (replaced by (1-x)KLBBNT-xNN) (x = 0.02, 0.04, 0.06, 0.08, 0.1) ceramics were fabricated by conventional solid-state reaction route. As the content of NaNbO3 increasing, an excellent dielectric temperature stability with a permittivity ∼2583 is obtained in the ceramic samples with x = 0.06. The temperature coefficient of capacitance (TCC) for x = 0.06 sample is less than ± 15% in the range of 58 °C to 338 °C. The XRD and temperature dependent permittivity results indicated that the large permittivity with excellent dielectric temperature stability maybe caused by NaNbO3 doping, which reduces the relaxation phase transition temperature of BNT-based ceramics and expands the temperature range of dielectric temperature stability. This work provides a new method to obtain BNT-based ceramic capacitors with large and stable dielectric constant in a wide temperature range.

Influence of heat sintering on the physical properties of bulk La0.67Ca0.33MnO3 perovskite manganite: role of oxygen in tuning the magnetocaloric response.

The effect of heat treatments on bulk poly-crystalline La0.67Ca0.33MnO3 perovskite manganite is presented, to explore the possible enhancement in magnetocaloric performance. Samples were prepared via conventional solid-state reaction route with annealing and sintering at various temperatures. Detailed measurements of temperature-dependent and field-dependent magnetization were carried out to estimate the Curie point and order of magnetic transition. The increased sintering temperature results in a steep transition near the TC, and establishes the magnetic sensitivity as well as the active zone for substantial magnetocaloric performance, at about 168.2% for the LCM9 (sintered at 900 °C) sample. The cause for the significant improvement in the magnetic and magnetocaloric response is brought to light using detailed X-ray photoelectron spectroscopy (XPS) analysis, highlighting the role of oxygen in modifying the Mn3+/Mn4+ charge ratio. The maximum value of the isothermal magnetic entropy change for the optimized sample is found to be 6.4 J kg-1 K-1, achieved at 269 K, while temperature-averaged entropy change (TEC) values, TEC(ΔTH-C = 3 K) and TEC(ΔTH-C = 5 K), of 6 J kg-1 K-1 and 5.2 J kg-1 K-1, respectively, were obtained with a low magnetic field change of 20 kOe. The obtained isothermal entropy change at low field for the optimized La0.67Ca0.33MnO3 sample is higher than that of pure Gd and most oxide-based materials. The relative cooling power (RCP) value is around 93 J kg-1 (ΔH = 20 kOe). The order of the phase transition is examined with universal scaling; the scaled entropy change curves confirm the collapse onto a single curve for LCM9, asserting second-order character, whereas the breakdown of the curve with a dispersion relation (d) of 101.1% at Θ = -5 confirms the onset of intrinsic first-order nature in the case of the high-temperature-sintered samples. Calorimetry measurements show thermal hysteresis of 2.4 K and 7.1 K for LCM11 (sintered at 1100 °C) at ramp rates of 5 K min-1 and 10 K min-1, respectively, confirming the first-order nature of the magnetic transition.

Anti-occupation defect dipole and gradient interface induced excellent giant permittivity in Sr0.95Bi0.05TiO3 ceramics

In this research, non-stoichiometric Bi doped SrTiO3 (ST) ceramics with nominal chemical formula of BixSr1-xTiO3 (x = 0, 0.01, 0.03, 0.05, 0.07) were produced through a conventional solid-state reaction route. A giant permittivity (ε) ∼30000 and low dielectric loss (tanδ) ∼0.03 were obtained in Bi0.05Sr0.95TiO3 ceramic. The temperature-ε and frequency-ε plots were conducted to investigate dielectric properties of the ceramics. The results of dielectric property plots revealed that the Bi0.05Sr0.95TiO3 ceramic has excellent dielectric stability within the range of 103–106 Hz and 30–250 °C. The fine scan XRD analysis, X-ray photoelectron spectrometer (XPS) and first principles calculation results showed that giant permittivity property of the Bi0.05Sr0.95TiO3 ceramic maybe attributed to the Bi‘Ti−VO∙∙−Bi‘Ti defect dipoles caused by Bi anti-occupation doping. And the gradient interface formed by Bi excessive doping also contributed to the giant permittivity. This study offers a new approach for achieving a giant permittivity with low dielectric loss in ST ceramic capacitors.

Enhanced power factor and thermoelectric efficiency in Cu2Sn1-xYxSe3 system: A low-temperature study

In the present study, we report the effect of Y doping at the Sn-site on structural, electrical, and low-temperature (10–350 K) thermoelectric properties of the Cu2SnSe3 system. The bulk polycrystalline samples of Cu2Sn1-xYxSe3 (0 ≤ x ≤ 0.12) are synthesized by the conventional solid-state reaction route method. Rietveld analysis of room temperature XRD data confirmed that the studied samples possess cubic crystal structure with F4‾3m space group. Temperature-dependent electrical resistivity of the samples with x ≤ 0.04 shows that they exhibit semiconducting behavior; while samples with x > 0.04 exhibit metallic behavior. In the studied temperature range, the Seebeck coefficient for all the samples is found to be positive, indicating that the majority of charge carriers are holes. A significant reduction in the electrical resistivity leads to an enhancement in the power factor, attaining a value of ∼253 μW/mK2 for the sample with x = 0.12 at 350 K. At high temperatures, the thermal conductivity of the samples decreases with temperature which is attributed to the phonon-phonon scattering. The systematic evolution of thermoelectric properties with Y incorporation over the range (0 ≤ x ≤ 0.12) shows the highest ZT of 0.024 at 350 K for the sample with x = 0.10, which is about six times higher than that of the pristine Cu2SnSe3. The results demonstrate that Y-doped compounds Cu2Sn1−xYxSe3 are potential candidates for thermoelectric applications.

Charge particle dynamics and electrochemical behaviour of SrTiO3-δ as anode material for IT-SOFC applications

SrTiO3-δ is a well-known metal oxide with cubic perovskite structure. In this work, we have synthesized SrTiO3-δ via conventional solid-state reaction route (SSR) and studied its electrochemical behaviour in three different pH media viz. 1 M aqueous solution of Na2SO4, (pH 7, neutral medium), KOH (pH 14, basic medium) and 0.5 M solution of H2SO4 (pH 1, acidic medium). The cubic phase with lattice constant, a = 3.905 Å is confirmed through XRD measurements. The electrical characterization of the sample was done in the frequency range 1Hz to 1 MHz and temperature range 25 oC–700 oC. The dynamics of the charged particles in the sample was studied using Jonscher power law. The scaling behaviour of the system has been investigated to understand the conduction mechanism. Further, charge carrier kinetics was also studied to understand the ionic contribution. Electrocatalysis was studied by cyclic voltammetry confirming the redox process in neutral and basic media, which was further confirmed in the XPS study. A better redox coupling occurs that was related to the Ti d-orbital and the O p-orbital interaction. The conductivity and catalytic properties of these materials indicated their use in different applications such as in fuel cells, sensors as well as in electrochemical devices.

Influence of Grain Size on Dielectric Behavior in Lead-Free 0.5 Ba(Zr0.2Ti0.8)O3-0.5 (Ba0.7Ca0.3)TiO3 Ceramics.

Fine-tuning of grain sizes can significantly influence the interaction between different dielectric phenomena, allowing the development of materials with tailored dielectric resistivity. By virtue of various synthesis mechanisms, a pathway to manipulate grain sizes and, consequently, tune the material's dielectric response is revealed. Understanding these intricate relationships between granulation and dielectric properties can pave the way for designing and optimizing materials for specific applications where tailored dielectric responses are sought. The experimental part involved the fabrication of dense BCT-BZT ceramics with different grain sizes by varying the synthesis (conventional solid-state reaction route and sol-gel) and consolidation methods. Both consolidation methods produced well-crystallized specimens, with Ba0.85Ca0.15O3Ti0.9Zr0.1 (BCTZ) perovskite as the major phase. Conventional sintering resulted in microstructured and submicron-structured BCT-BZT ceramics, with average grain sizes of 2.35 μm for the solid-state sample and 0.91 μm for the sol-gel synthesized ceramic. However, spark plasma sintering produced a nanocrystalline specimen with an average grain size of 67.5 nm. As the grain size decreases, there is a noticeable decrease in the maximum permittivity, a significant reduction in dielectric losses, and a shifting of the Curie temperature towards lower values.

Influence of particle size of initial oxides on the dielectric properties of ilmenite-type Zn0.7Mg0.3TiO3 ceramics

The core of this research is to elucidate the effect of the particle size of the starting oxide on the dielectric properties of Zn0.7Mg0.3TiO3 ceramics. The study was carried out using a conventional solid-state reaction route. The microstructure optimization of Zn0.7Mg0.3TiO3 ceramics was achieved by introducing nanoscale particles. The distortion of octahedral [TiO6] and the effect of crystal structure led to significant changes in the dielectric properties. Stability analysis shows that usage of nanoparticles decreases the temperature stability of Zn0.7Mg0.3TiO3 ceramics. This work will offer a well-defined guideline for the selection of raw materials to prepare ceramics in the practical production process.

Synthesis and characterization of (Ba (1.6-3/2X) Sr2.4Na2Nb10O30: xHo3+) ferroelectric nanomaterials by solid state reaction routes for device applications

Barium Strontium Sodium Niobate (Ba (1.6-3/2X)Sr2.4Na2Nb10O30:xHo3+) tungsten bronze structured ferroelectrics nanomaterial synthesized by conventional solid state reaction route is investigated. The X-ray diffraction (XRD), the scanning electron spectroscopy (SEM), energy dispersive x-ray spectroscopy (EDS), Fourier transform-infrared spectroscopy (FTIR) and UV–Vis Spectroscopy were used to study the structure, surface morphology/microstructure, elemental composition/mapping, functional groups identification and absorption, respectively. The XRD pattern revealed Tetragonal Tungsten Bronze structured crystallite phase that matches with the JCPDS card number -00-039-1453 having space group of p4bm and lattice parameters of a = 12.33 Å, b = 12.33 Å and c = 3.93 Å. The average crystallite size of the synthesized samples obtained at the prominent peak (311) for position/2ϴ = 32.320 is 67.52 nm. The SEM images showed that surface microstructures have random and nearly uniform distribution of nanoparticles with different shapes and size on the surface. Moreover, less porous surface microstructure was obtained and it is promising for enhancing ferroelectric properties. EDS analysis confirmed the presence of all the constituent elements with their proportional atomic and molecular weight ratios. For the pure metal oxide, the FTIR results showed the bond vibration mode at wavenumber of 540.60 cm−1, having only single collective metal oxide intense peak without impurities. For Ho3+ concentration corresponding to 0.05 and 0.10 %, additional peaks were observed at 429.92 cm−1 and 415.77 cm−1, respectively, confirming the existence of Ho–O bond vibration modes. The UV–vis results show that the absorption edges of all samples are at the same wavelength region (approximately 205 nm). Moreover, it was observed that the optimum absorption intensity was obtained for 0.03 % Ho3+ ions concentration.

Exploration of the Structural, Dielectric, Ferroelectric, and Piezoelectric Properties in Non-stoichiometric Sr1−XBi2+2X/3Nb2O9 Ceramics

In this study, the authors focused on the preparation and characterization of Lead-free ferroelectric ceramics known as Sr1−XBi2+2X/3Nb2O9: SBBNX, where 0.0≤ × ≤0.4. The ceramics were synthesized using a conventional solid-state reaction route. The researchers performed X-ray diffraction (XRD) analysis to confirm the phase formation and employed the Rietveld refinement technique. The results indicated that the prepared SBBNX ceramics exhibited a single phase with an orthorhombic structure, specifically belonging to the A21am space group. All samples were subjected to analysis using field emission scanning electron microscopy (FESEM) to investigate their surface morphology. The micrographs revealed a uniform distribution of grains (of size 2–4 μm ) on the surface, with distinct grain boundaries. An increasing trend in both the dielectric constant (from 99 to 220 at room temperature) and transition temperature (from 396 °C to 490 °C) was noted with an increase of Bi content in SBN. The researchers estimated the activation energies by analyzing the Arrhenius plots of the ac conductivity. The obtained values ranged from 0.62 to 1.25 eV, indicating the presence of motion of oxygen vacancies in the SBBNX ceramics. The primary objective of this study was to optimize the Sr/Bi ratio in SBBNX ceramics to enhance their potential use in non-volatile random access memory (NVRAM) applications and high-temperature piezoelectric devices.

Fabrication of fuel electrode supported proton conducting SOFC via EPD of La2Ce2O7 electrolyte and its performance evaluation

The proton conducting La2Ce2O7 electrolyte has already been shown to be chemically more stable to H2O and CO2 than BaCeO3 based electrolyte materials. It has become widely popular as an alternative electrolyte for low to intermediate temperature operation in solid oxide fuel cells. Few initial studies have reported the fabrication of LCO-based fuel cells using the co-pressing process. Here, we present an alternative, simple, cost-effective and efficient method for the deposition of uniform and dense La2Ce2O7 electrolyte coatings, which is a key requirement for any fuel cell fabrication process. In this work, La2Ce2O7 is synthesized by a conventional solid state reaction route and we have established the process of fuel cell fabrication followed by its investigation for SOFC application as electrolyte material. Different alcohols (e.g. butanol, ethanol, acetone, acetyl acetone and isopropanol) are used as dispersion medium, the suspension chemistry and subsequent coating of LCO powders by electrophoretic deposition are investigated. A thin and good quality coating of about 11 μm thickness is obtained in an ethanol-based suspension under deposition conditions at 50 V for 2 min. Fuel electrode supported half cells with LCO electrolyte fabricated by electrophoretic deposition and performance test of fabricated cell is evaluated in moist H2 (∼3% H2O) as reducing medium and static air as oxidizing medium.

Structural, dielectric and electronic properties of Ba1-xSrxZr0.3Ti0.7O3 (x = 0.0, 0.1, 0.2, 0.24, 0.27, 0.3) ceramics: Combined experimental and ab-initio study

Ba1-xSrxZr0.3Ti0.7O3 (x = 0.0, 0.1, 0.2, 0.24, 0.27 and 0.3) materials were synthesized using conventional solid state reaction route. Structural properties were investigated using X-ray diffraction analysis. All the samples reveal single phase structure. The dielectric properties of all the samples were investigated at different temperatures of 100 K to 300 K, and at different frequencies of 1 kHz to 500 kHz. The diffusivity rises with increase in Sr divalent cation concentration. It is seemed that with increase in Sr2+ concentration the transition temperature reduces for all compositions. This may because of the introduction of Sr2+ by replacing Ba2+ since Sr+2 has smaller ionic radius than Ba+2. Moreover, the dielectric constant maxima for Ba1-xSrxTi0.7Zr0.3O3 increases up to x = 0.24 and then further increment in Sr content up to x = 0.3, the maxima of dielectric constant shows decrease. Moreover, charge conduction mechanism and optical response of Ba1-xSrxZe0.3Ti0.7O3 (x = 0.0, 0.1, 0.2, 0.3) has been calculated theoretically by using CASTEP. Herein, the calculated density of states (DOS) and three dimensional integrated charge density reveal that concentration of Sr in Ba1-xSrxZe0.3Ti0.7O3 (x = 0.1, 0.2, 0.3) causes variation in energy band gap. As regards optical response of Ba1-xSrxTi0.7Zr0.3O3, with x = 0.3 the high frequency absorption decreases to minimal value in accordance to experimental findings.

Analysis of amplitude and frequency-dependent scaling behavior of dynamic hysteresis loop and thermal properties of BaZr0.05Ti0.95O3 ceramic

In this work, single-phase BaZr0.05Ti0.95O3 (BZT) ceramic was prepared through a conventional solid-state reaction route. The structural identity was analyzed by X-ray diffraction (XRD) and Rietveld refinement, which reveals the single-phase perovskite structure of the synthesized sample having an orthorhombic structure and space group Amm2. Scanning electron microscope (SEM) study gives an idea about the well-dense grains with clear grain boundaries of the BZT sample. Frequency and amplitude-dependent Polarization-Electric field (P-E) and Strain-Electric field (S-E) loops were studied. The parameters like remnant polarization (Ec), coercive field (Pr), loop area (<A>), energy storage efficiency (η), field-induced maximum strain (Smax) and inverse piezoelectric coefficient (d33*) were calculated. The scaling behavior of the hysteresis loops area as a function of frequency and field strength is studied. The thermal conductivity and thermal diffusivity as a function of temperature were investigated.

Cr3+ doping-controlled magnetic and dielectric properties of polycrystalline Y-type BaSrCo2Fe11-xCrxAlO22 hexaferrite

The trend towards multifunctionality and integrating electronic devices has led to the exploration of Y-type hexaferrite with excellent magnetic and dielectric properties. The Y-type hexaferrite BaSrCo2Fe11-xCrxAlO22 (0.0 ≤ x ≤ 0.5, with step of 0.1) ceramics have been prepared by conventional solid state reaction route. The phase structure, microscopic morphology, magnetic and dielectric properties of Y-type hexaferrite with chromium substitution are studied in detail. The analysis of XRD, SEM and EDS reveals that the lattice parameters and grain size decrease with the increase of Cr content. XPS results show the coexistence of Fe2+ and Fe3+. All samples exhibit well-defined ferromagnetic hysteresis loops at room temperature and the Cr3+ doping enhances the saturation magnetization and coercivity. The dielectric constants for all samples are found in the range of 10–15 and the dielectric loss is less than 0.02 at high frequency. The resistivity demonstrates that the samples possess high insulating nature with all above 2 × 109 Ω·cm, with a maximum value of 9.5 × 109 Ω·cm for x = 0.2. These results reveal that Cr3+ doped Y type hexaferrite could have potential applications in multifunctional electronic devices.

Multifunctional behavior of solid-state derived Ca-doped BaFe0.5Nb0.5O3 complex perovskite system

In recent years, BaFe0.5Nb0.5O3 (BFN) complex perovskite has been projected as one of the promising Pb-free materials for energy storage applications. The primary goal of this research work is to look into the impact of Ca on the structural, electrical, and magnetic behavior of BFN and examine its suitability for multifunctional applications. The conventional solid-state reaction route is followed to prepare the desired Ba0.88Ca0.12Fe0.5Nb0.5O3 complex perovskite sample. The analysis of X-ray diffraction data reveals that the sample crystallizes in monoclinic symmetry and belongs to the C1m1 space group. The micrograph obtained through scanning electron microscopy indicates the dense surface morphology of the sample. The elemental examination through energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy confirms the purity and reveals information regarding the chemical states of the involved elements. The complex impedance and dielectric studies conducted over a wide frequency and temperature range infer that the sample possesses semiconducting as well as capacitive properties. The magnetic response monitored at room temperature confirms the ferromagnetic behavior of the sample. Based on all the investigations carried out, it can be stated that the synthesized complex perovskite can be used for fabricating tunable microwave devices, energy storage devices, magnetic storage devices, etc.

Electric and dielectric studies of MgCuZn ferrites

Mg0.5- x Cu x Zn0.5Fe2O4 (where x = 0.0, 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3) ferrites were synthesized by conventional solid state reaction route and were sintered at 1200 °C using a programmable furnace. These sintered MgCuZn ferrites were characterized by X-ray diffraction (XRD). The single phase of the ferrites was confirmed from the X-ray diffraction studies. The dielectric studies, ac, dc electrical conductivity studies were performed with the variation of Cu content, and temperature. The results are discussed in the light of Koops theory and polaron hopping.

Optimized Strain Response in (Co0.5Nb0.5)4+-Doped 76Bi0.5Na0.5TiO3-24SrTiO3 Relaxors

High strain with low hysteresis is crucial for commercial applications in high precision actuators. However, the clear conflict between the high strain and low hysteresis in BNT-based ceramics has long been an obstacle to actual precise actuating or positioning applications. To obtain piezoceramics with high strain and low hysteresis, it is necessary to enhance the electrostrictive effect and develop an ergodic relaxor (ER) and nonergodic relaxor (NR) phase boundary under ambient conditions. In this work, (Co0.5Nb0.5)4+ doped 76Bi0.5Na0.5TiO3-24SrTiO3 (BNST24) relaxors were fabricated using the conventional solid state reaction route. X-ray diffraction patterns revealed the B-site substitution in BNST24 ceramics. By adjusting the (Co0.5Nb0.5)4+ doping in BNST24, we effectively tuned the TNR-ER and Td close to ambient temperature, which contributed to the development of the ergodic relaxor phase and enhanced the electrostrictive effect at ambient temperature. The I-P-E loops and bipolar strain curves verified the gradual evolution from NR to ER states, while the enhanced electrostrictive effect was verified by the nearly linear S-P2 curves and improved electrostrictive coefficient of the BNST24-xCN relaxors. An enhanced strain of 0.34% (d*33 = 483 pm/V) with low hysteresis of 8.9% was simultaneously achieved in the BNST24-0.02CN relaxors. The enhanced strain was mainly attributed to the proximity effect at the ER and NR phase boundary of BNST24-0.02CN, while the improved electrostrictive effect contributed to the reduced strain hysteresis. Our work demonstrates an effective strategy for balancing the paradox of high strain and low hysteresis in piezoceramics.

Study of photoluminescence behaviors and Judd-Ofelt analysis of Eu3+ doped double perovskite Ba2GdSbO6 phosphor for highly pure and strong red-light generation

An array of Eu3+ doped Ba2GdSbO6 luminescent materials have been synthesized by the conventional solid-state (high temperature) reaction route. Surface morphology has been studied via Field Emission Scanning Electron Microscopy. The structural and optical behaviors have been studied using X-Ray Diffraction (XRD), FTIR, Raman spectroscopy, Diffuse reflectance spectroscopy, Photoluminescence excitation (PLE), and Photoluminescence emission (PL) spectra. FTIR and Raman's spectra provided the chemical functional group and different vibrational levels within the samples. The calculated optical band gap was 4.40 eV and 4.47eV for pure and optimized samples respectively. Photoluminescence emission curves have been recorded for 245 nm of excitation wavelength and the highest emission peak was focused at 595 nm corresponding to 5D0 → 7F1. Similarly, the Photoluminescence excitation curves were monitored at the emission wavelength of 595 nm and a broad charge transfer band (CTB) was observed from 230 to 285 nm. The emission spectra show the concentration quenching effect beyond the 2 mol% Eu3+ concentration. The corresponding transitions of Eu3+ were further utilized to obtain the Judd-Ofelt (J-O) transition intensity parameters Ωλ (λ = 2, 4) for each sample. Additionally, by studying decay kinetics, the average lifetime of the red emission of the samples has been evaluated, which was 4.622 ms. The photometric study also reveals the CIE coordinates, color purity and CCT values of the proposed phosphor material. Thus, the results obtained from these characterizations, suggest that the prepared sample may behave as a potential candidate in the case of UV-excited red light-emitting phosphor material for light-emitting diodes and field emission devices.

Highly efficient far-red emitting Mn4+-activated Li3La3W2O12 phosphors for plant growth LED lighting

High-efficiency far-red emitting phosphors with an emission peak of around 730 nm are urgently needed for indoor plant growth light-emitting diode (LED) lighting. In this article, we report on the synthesis, crystal structure, and luminescence properties of a new highly efficient Mn4+ ion-activated Li3La3W2O12 (LLWO) far-red emitting phosphor. A group of LLWO:Mn4+ phosphors doped with different Mn4+ ion concentrations have been prepared via the conventional high-temperature solid-state reaction route. X-ray diffraction Rietveld refinement reveals that the LLWO:Mn4+ phosphor has the monoclinic structure with space group P21/n, along with lattice parameters of a = 5.5396 Å, b = 5.6026 Å, c = 7.8802 Å, α = γ = 90°, β = 90.0988°, and V = 244.57 Å3. Interestingly, LLWO:Mn4+ phosphors can generate bright narrowband far-red emission in the 650–800 nm wavelength range peaking at 719 nm due to the spin- and parity-forbidden 2Eg→4A2g transition of Mn4+ ions, matching well with the absorption spectrum of phytochrome PFR. The excitation spectrum monitored at 719 nm has a broad excitation band with the range from 250 to 550 nm centered at 339 nm and 472 nm, indicating that LLWO:Mn4+ phosphors could be efficiently pumped by both ultraviolet and blue LED chips. The highest far-red emission is achieved for the sample doped with 1.2 mol% Mn4+ ion, and this optimal LLWO:1.2%Mn4+ sample shows a high internal quantum efficiency of 88.4% and a decay lifetime of 2.289 ms. Commission Internationale de l’Eclairage (CIE) color coordinates of LLWO:1.2%Mn4+ are determined to be (0.7326, 0.2674). Besides, the crystal field analysis and temperature-dependent emission spectra of the as-prepared samples have been investigated in detail. The emission intensity of LLWO:1.2%Mn4+ sample at 423 K remains about 40% of that at 303 K. Finally, a LED device is fabricated by integrating the LLWO:1.2%Mn4+ phosphors and a 460 nm blue LED chip, which shows bright blue and far-red dual emission bands under 20–300 mA driving currents. This work demonstrates that these newly developed far-red emitting LLWO:Mn4+ phosphors have excellent application prospects in plant growth LED lighting.

Investigation of frequency dependent dielectric properties of La-doped BaSnO3-ZnSnO3 solid-solutions

In this study, we report the structural, optical, and dielectric properties for La-doped BaSnO3 and ZnSnO3 solid solutions, La0.03(Ba1−xZnx)0.97SnO3 (x = 0,0.1,0.5,1) prepared at 1100 °C by isovalent substitution of Zn+2 at the Ba+2 site using the conventional solid-state reaction route. Structural data shows the transformation from cubic perovskite to orthorhombic perovskite structure as the amount of Zn increases in La-doped BSO samples. A minor pyrochlore phases, La2Sn2O7 and Ba2SnO4 were found in the XRD. This paper mainly focuses on understanding the contribution of physical phenomena of ac conductivity in terms of dielectric properties. The dielectric properties of the composites follow non-Debye type behavior. There was a moderate increase in the dielectric constant from 10.07 to 334 at 20 Hz, and 2.99–133 at 1 kHz, respectively, as we increased the amount of Zn, which is high as compared with other reported dielectric materials. By using Jonscher's power law, ac conductivity was found to increase in LZSO samples. This conduction mechanism due to the hopping of ions between coordination sites present in the composite and can be understood by the classically correlated barrier hopping phenomenon. Furthermore, the trivial loss of electromagnetic waves over a given frequency range demonstrates the great potential of La-doped ZnSnO3 materials to be utilized in ground penetrating radar systems, communication systems, and energy storage devices.