Comprehension of the photoinduced charge transfer assisted energy transfer in Gd3+-based host sensitized tellurate phosphors for thermal sensing and anticounterfeiting labels.

A series of novel Eu3+-activated Ba2Gd2/3TeO6 (BGT) phosphors were successfully synthesised via a high temperature solid state reaction method. The crystal structure analysis showed that Eu3+-doped Ba2Gd2/3TeO6 double perovskite phosphors possess monoclinic symmetry with space group P21/n. The as-prepared phosphors can be efficiently excited by far-ultraviolet light to generate reddish orange luminescence of around 593 nm corresponding to the 5D0 → 7F1 transitions of Eu3+ ions. Gd3+ acts as a sensitizer for luminescence enhancement. The highest luminescence intensity corresponded to x = 0.11 Eu3+ concentration, and the critical distance was calculated to be 9.61 Å, indicating that multipolar interaction is behind the concentration quenching mechanism. Besides, the optimum concentration Eu3+-activated Ba2Gd2/3TeO6 phosphor exhibited color co-ordinates of (0.63, 0.36), a high color purity of 94.21% and a quantum efficiency of 18%. JO intensity parameters reveal the slight distortion of the crystal field around the activator ion. Notably, the maximum relative sensitivities of the BGT:0.11Eu3+ phosphor were found to be 0.19% K-1 within the temperature range of 300-500 K and 2.07% K-1 within 80-300 K, and it can potentially be used as a promising thermometer in high and low temperature regions, respectively. The luminescent labels based on fluorescent ink and PL chalk demonstrate the potential application of synthesized phosphors in anti-counterfeiting and security labeling.

Enhancing the inherent NIR photoluminescence in SrLaLiTeO6 through Cr3+-Yb3+ co-substitution for high performance pc-LEDs.

Until now, double perovskite tellurates have not been reported to exhibit inherent NIR photoluminescence. Therefore, the current study's revelation of inherent NIR luminescence in SrLaLiTeO6 double perovskite centered at 970 nm under 340 nm excitation is particularly intriguing. This phenomenon is attributed to the photoluminescence of Te4+ ions. This study also examines the NIR luminescence of Cr3+-Yb3+ co-doped SrLaLiTeO6. The host and SrLaLiTeO6:3%Cr3+, y%Yb3+ (y = 1, 2, 4, 6, 8, 10 mol%) were synthesized using the solid-state ceramic route. The successful incorporation of Cr3+ and Yb3+ ions into the host lattice was confirmed through XRD, Raman, and diffuse reflectance spectral analyses. Under 270 nm excitation, the photoluminescence (PL) of SrLaLiTeO6:Cr3+ exhibits a blueshift of the PL band to 965 nm due to the 4T2(4F) → 4A2g(4F) emission component of Cr3+ ions. The excited-state lifetime of SrLaLiTeO6:0.5%Cr3+ was measured at 36 µs, but this decreased to 26 µs as the Cr3+ concentration reached 10 mol%, primarily due to the enhancement of non-radiative energy transfer between Cr3+ ions. Incorporating Yb3+ into the system results in additional spectral lines with an enhanced intensity in the range of 970 nm to 1125 nm when excited at 270 nm. These emission lines correspond to the 2F5/2 → 2F7/2 transitions of Yb3+ ions, indicating an efficient energy transfer from Cr3+ to Yb3+. Furthermore, the study also reveals that Yb3+ emission is observed even without Cr3+ ions in SrLaLiTeO6 under 340 nm excitation, suggesting the possibility of energy transfer from the host to Yb3+ ions. The thermal stability and crystal field parameters of the synthesized phosphors are also explained in detail. To explore the potential of these phosphors in practical applications, phosphor-converted NIR LEDs were fabricated using SrLaLiTeO6, SrLaLiTeO6:3% Cr3+, and SrLaLiTeO6:3% Cr3+, 1%Yb3+.

Augmenting cyan emission in vanadate garnets via Dy3+activation for light emitting devices and multi-mode optical thermometry.

Developing cyan-based phosphors is inevitable to bridge the cyan gap to generate white light with a high color rendering index. Herein, the blue-green emission from the VO43- center in the Sr2NaMg2V3O12 host is augmented via activating with Dy3+ ions. Dual emission from the Sr2NaMg2V3O12:Dy3+ system under 335 nm excitation is due to the energy transfer from VO43- to the Dy3+ center. An increase in the ratio of yellow to blue bands (Y/B) is noted with the increase in the concentration of Dy3+. Apart from the higher activation energy of 0.41 eV, excellent color stability with a small thermochromic shift is noted at elevated temperatures. The light emitting device fabricated based on the Sr2NaMg2V3O12:Dy3+ phosphor presents bright cyan emission with CIE coordinates of (0.250, 0.352), a CCT of 9826 K, and a CRI of 53 with stable emission even at higher input currents. The application of Sr2NaMg2V3O12:Dy3+ in multi-mode temperature sensing is also discussed. The maximum relative temperature sensitivity of 1.32, 0.41, and 1.9% K-1 at 380, 300, and 460 K is obtained for the fluorescence, fluorescence intensity ratio and excitation intensity ratio methods. Thus, the present work details the capability of Dy3+-based vanadate garnet phosphors for solid-state lighting and temperature sensing.

Strategic Tuning of Photophysical Response in the Polyhedral Framework of the Garnet Structure toward White Light-Emitting Devices with Enhanced Color Rendering.

Designing a single-phase phosphor with high quantum efficiency and full spectrum emission is inevitable for today's scientific world. Herein, an optimal strategy for realizing white emission in a single component matrix is envisaged based on the structure-property-design-device policy. Cationic substitution corresponding to polyhedral expansion and contraction in A2A'B2V3O12 confirms the existence of strong and intricate linkage in the garnet structure. The dodecahedral expansion causes compression of VO4 tetrahedra and a blue shift. The direct correlation of V-O bond distance with red shift validates the distortion of the VO4 tetrahedra. The interdependence of photophysical properties via cationic substitution and subsequent correlation of the V-O bond distance with emission bands enabled the tailoring of phosphor-CaSrNaMg2V3O12 with a high quantum efficiency of 52% and excellent thermal stability of 0.39 eV. Bright warm white light-emitting diode (WLED) devices are fabricated based on Eu3+ and Sm3+-activators. A high quantum efficiency-74% is obtained for the designed Eu3+ phosphor. CIE coordinates near the achromatic point (0.329, 0.366), low CCT-5623 K, and high color rendering index (CRI)-87 are obtained for the single-phase WLED device. This work puts forth a new direction for designing and engineering promising WLEDs with enhanced color rendering based on single-phase phosphors with full spectrum emission.

Design and Fabrication of Layered Electromagnetic Interference Shielding Materials: A Cost-Effective Strategy for Performance Prediction and Efficiency Tuning.

The electromagnetic interference (EMI) shielding market is one of the fast-growing sectors owing to the increasingly complicated electromagnetic environment. Recently, priority has been given to improvise the techniques to fine-tune and predict the shielding properties of structures without exhausting raw materials and reduce the expense as well as the time required for optimization. In this article, we demonstrate an effective and precise method to predict the EMI shielding effectiveness (SE) of materials via simulating the performance of composites having alternate layers of conducting and magnetic materials in a virtual waveguide measurement environment based on the finite element method (FEM). The EMI SE of multilayered heterogeneous arrangements (MHAs) is simulated in the K-band region using ANSYS High Frequency Structure Simulator (HFSS) software, which can be extended to all other bands as well. Various simulations carried out by changing the order of the conducting and magnetic layers and the number of layers revealed that the strategic arrangement of electromagnetic (EM) energy-trapping layers inside the impedance-matching layers in the MHAs significantly contributes toward the enhancement of absorption-dominated EMI shielding. Among the MHAs, the conducting-magnetic-conducting (CMC) systems exhibited the highest shielding effectiveness of above 50 dB. The MHAs are realized for testing using poly(vinylidene fluoride)-based composites of low-cost carbon black and barium hexaferrite, an easily accessible ferrite. Through this study, we propose the idea that materials with high production cost and cumbersome fabrication procedures are not necessary to realize highly efficient shielding materials.

Green Route for the Synthesis of Fluorescent Carbon Nanoparticles from Circassian Seeds for Fe(III) Ion Detection.

A facile and green strategy was carried out for the preparation of fluorescent carbon nanoparticles (CNp) using non-toxic circassian seeds as carbon precursor (CNp, named ACNp). The surface of amorphous ACNp is latched with different surface moieties such as hydroxyl, carbonyl, ether and amino groups and it is confirmed by FTIR and XPS. These functionalities provide high solubility and stability to ACNp in aqueous medium. The surface of ACNp is highly negatively charged due to the presence of oxygen rich functional groups and it is confirmed by zeta potential. A reasonably good quantum yield (QY) of 5.1% is obtained for ACNp compared to other CNp derived from bioprecursors without any surface passivation. Circassian seeds are self sufficient for the synthesis of N doped CNp. The excitation dependent fluorescence property of ACNp is invariant under ionic and thermal environments. They exhibit good selectivity towards Fe3+ ions via static quenching mechanism with detection limit of 32.7 µM.

Room-Temperature Ferromagnetic Sr3YCo4O10+δ and Carbon Black-Reinforced Polyvinylidenefluoride Composites toward High-Performance Electromagnetic Interference Shielding.

In this study, we fabricated composites of conducting carbon black (CB), room-temperature ferromagnetic Sr3YCo4O10+δ (SYCO) and polyvinylidenefluoride (PVDF) by the solution mixing and coagulation method for the first time. During the nucleation process of PVDF, the presence of SYCO and CB individually facilitates the crystallization of polar ß and semipolar γ phases along with the nonpolar α phase in PVDF. The dc electrical conductivity of PVDF raised from 1.54 × 10-8 to 9.97 S/m with the addition of 30 wt % of CB, and it is nearly constant with respect to the SYCO content. The PVDF/CB/SYCO composites (PCS) possess high permittivity and its variation is in accordance with the content of polar phases in PVDF. Moreover, the complex permittivity and permeability spectra from 10 MHz to 1 GHz indicate that the dielectric loss dictates over magnetic loss in these composites. The electromagnetic interference shielding effectiveness (EMI SE) of PCS composites is higher than that of PVDF/CB and PVDF/SYCO composites in the 8.2-18 GHz region. Addition of SYCO in the PVDF/CB matrix enhances shielding by dominated absorption with minimal reflection. The analysis of the shielding mechanism suggests that in addition to conducting and magnetic losses due to CB and SYCO, respectively, the synergy among CB, SYCO, and PVDF promotes shielding by matching the input impedance to that of free space, enhancing multiple internal reflections from SYCO and subsequent absorption by CB, eddy current losses, dielectric damping losses, interfacial polarization losses, and so forth. These different mechanisms result in an enhanced EMI SE of 50.2 dB for the PCS-40 composite for a thickness of 2.5 mm.

Structural Characterization of B-Site Ordered Ba2Ln2/3TeO6 (Ln = La, Pr, Nd, Sm, and Eu) Double Perovskites and Probing Its Luminescence as Eu3+ Phosphor Hosts.

Ba2Ln2/3TeO6 (Ln = La, Pr, Nd, Sm, and Eu) double perovskites were synthesized via solid-state ceramic route. Preliminary X-ray diffraction studies indicated a pseudocubic structure with lattice parameters ranging from 8.55 to 8.44 Å for the substitution of rare earths from La to Eu. Raman spectra show the frequency dependence of various Raman bands with respect to rare-earth substitution and exhibit a significant shift in peaks to higher wavenumber region, which was observed only for symmetric stretching modes of LnO6 and TeO6 octahedra. In accordance with observed number of bands and group theoretical predictions, the most likely symmetry of all compounds in the Ba2Ln2/3TeO6 system was found to be monoclinic with P21 /n space group. Rietveld refinement of the XRD patterns further confirmed the P21 /n space group and also the 1:1 rock salt ordering of the B-site cations. Diffuse reflectance spectra of Ba2Ln2/3TeO6 showed the optical bandgaps of these compounds between 3.9 and 4.8 eV, indicating the suitability as luminescent host material. The reduction in bandgap energy with lanthanide contraction of rare-earth ions is attributed to the widening of conduction band with octahedral tilting. Photoluminescence (PL) spectra and PL excitation spectra of Ba2La2/3- xEu xTeO6 ( x = 0.025, 0.05, 0.075, 0.1, 0.125, 0.15) were investigated and found to exhibit bright orange-red emission under UV excitation. Chromaticity coordinates closely resemble those of commercial red phosphor Sr2Si5N8:Eu2+, which points toward the possible applicability of these new red phosphors in solid-state lighting industry. Finally, Judd-Ofelt intensity parameters Ωλ (λ = 2 and 4) were calculated, which indicate that Eu3+ ions occupy the symmetric octahedral B-site of the Ba2La2/3TeO6.

Sr2FeO3 with stacked infinite chains of FeO4 square planes.

The synthesis of Sr2FeO3 through a hydride reduction of the Ruddlesden-Popper layered perovskite Sr2FeO4 is reported. Rietveld refinements using synchrotron and neutron powder diffraction data revealed that the structure contains corner-shared FeO4 square-planar chains running along the [010] axis, being isostructural with Sr2CuO3 (Immm space group). Fairly strong Fe-O-Fe and Fe-Fe interactions along [010] and [100], respectively, make it an S = 2 quasi two-dimensional (2D) rectangular lattice antiferromagnet. This compound represents the end-member (n = 1) of the serial system Sr(n+1)FenO(2n+1), together with previously reported Sr3Fe2O5 (n = 2) and SrFeO2 (n = ∞), thus giving an opportunity to study the 2D-to-3D dimensional crossover. Neutron diffraction and Mössbauer spectroscopy show the occurrence of G-type antiferromagnetic order below 179 K, which is, because of dimensional reduction, significantly lower than those of the other members, 296 K in Sr3Fe2O5 and 468 K in SrFeO2. However, the temperature dependence of magnetic moment shows a universal behavior.