Correlation between structural and optical properties of Dy3+ doped BaGd2O4 phosphors intended for solid-state lighting applications

Highly crystalline and single phase BaGd${}_{2-x}$Dy${}_x$O${}_4$ (0.00 $\le$x $\le$ 0.16) phosphors, with an average crystallite size around 126 nm, have been synthesised using solid-state reaction technique. The structural and optical properties of these phosphors have been studied in detail to establish an unambiguous correlation between these properties. High-angle annular dark field (HAADF) images have confirmed that the constituent elements are homogeneously distributed in the particles, and their elemental composition has been established using X-ray photoelectron spectroscopy (XPS). The tuning of optical band gap with x has been achieved, which is a rare achievement in these phosphors. Also, the optimum concentration of Dy${}^{3+}$ ions has been found to be 0.8 mol%, which is the lowest among the Dy${}^{3+}$ doped BaGd${}_2$O${}_4$ phosphors reported so far. This concentration quenching effect has been discussed on the basis of a combination of decay curve analysis, calculation of average critical distance between the Dy${}^{3+}$ ions and integrated intensities of photoluminescence (PL) emission bands. The average crystallite size and optical band gap has also been found to decrease after x = 0.016, from which their correlation with concentration quenching effect has been investigated. The asymmetry ratio between the integrated intensities of yellow and blue PL emission bands has been observed to be greater than 2 throughout x, which confirmed the preferential lattice site for Dy${}^{3+}$ ions in these phosphors with present synthesis conditions. The variation of asymmetry ratio and Gd${}^{3+}$-dominated IR-active lattice vibrations with x, and Vegard’s law pertaining to the volume of a unit cell confirms that the local bonding environment in the lattice of these phosphors gets modified at x = 0.016. The photometric parameters for these phosphors reveal their suitability for fabrication of warm light orange LEDs on appropriate UV chips.     

Effects of varying Alx moles on structure and luminescence properties of ZnAlxO1.5x+1:0.1 mol% Tb3+ nanophosphors prepared using citrate sol-gel method

Un-doped and ZnAl_xO_1.5x+1:0.1 mol% Tb³⁺(ZAOT) nano-powders were synthesized via citrate sol-gel method.The AI_x moles were varied in the range of 0.25 ≤x ≤5.0.The X-ray powder diffraction(XRD)data reveal that for x <1.5,the prepared samples crystal structure consists of mixed phases of the cubic ZnAl₂O₄ and hexagonal ZnO phases,while for x> 1.5 the structure consists of single phase of cubic ZnAl₂O₄.The ...     

Fabrication of superhydrophobic surfaces on a glass substrate via hot embossing

This study developed a new hot pressing process to prepare superhydrophobic surfaces with controllable shape and size on a glass substrate. Microstructures were fabricated on tungsten carbide mold via picosecond laser processing. Microgroove structures were reproduced on glass during the hot embossing process and SiO₂ nanoparticles laid on the mold were also embedded into the glass surface under the action of heat and pressure to provide nanostructures. The contact angle of the superhydrophobic glass surface reached up to 161.8°, and the sliding angle was only 3°. The structures and chemical composition of superhydrophobic glass surface were identified by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD), and Fourier transformed infrared (FTIR) spectroscopy. The 3D laser scanning microscopy result showed the height (20 μm) of the microgroove structures, while white light interferometry revealed the surface roughness (Ra 2.725 μm). The superhydrophobic glass surface demonstrated satisfactory temperature resistance and chemical stability through temperature and acid and alkali solution immersion tests. The surface exhibited certain mechanical stability by friction and wear test. This work provides a new hot embossing method for solving the problem of structural consistency and mass production of superhydrophobic glass, and will have great application prospects in the engineering field.     

Preparation of M2B5O9Cl:Eu2+(M=Sr,Ca) blue phosphors by a facile low-temperature self-reduction method and their enhanced luminescent properties

In this work,through a facile method of low-temperature(only 350 ℃) self-reduction,1D nano-sized M₂B₅O₉CI:Eu²⁺(M=Sr,Ca) blue phosphors with highly efficient performance can be obtained.The crystal structure,morphology and photoluminescence(PL) properties including thermal stability of M₂B₅O₉CI:Eu²⁺(M=Sr,Ca) phosphors were investigated.The M₂B₅O₉CI:Eu²⁺(M=Sr,Ca) phos...     

Two temperature-dependent 2D heterometallic Cd(II)–Dy(III) coordination polymers exhibiting slow magnetic relaxation and luminescence properties

Two unique two-dimensional (2D) Cd(II)–Dy(III) heterometallic coordination polymers, {[DyCd(HPMA)(PMA)₂(H₂O)₄]·2H₂O}_n (1) and [DyCd(PAA)(PMA)₂(H₂O)₃]_n (2, PAA^– = phenylacetate), were prepared successfully based on the phenylmalonic acid (H₂PMA). The construction of two polymers is sensitive to the reaction temperature and can be synthesized directionally at room temperature and 90 °C, respectively. Complexes 1 and 2 display 2D layer structures that include dinuclear [Dy₂] cluster node and Dy(III)-based 1D zigzag chain motif severally. The Dy(III)-based units in two structures both are spaced well with the adjacent ones by the diamagnetic Cd(II)-based moieties. The magnetic studies reveal that 1 and 2 both display slow magnetic relaxation with temperature-dependent relaxation peaks producing an effective energy barrier (Δτ) of 74.5 and 32.1 K, separately. Furthermore, the solid-state photophysical properties of 1 and 2 show strong characteristic luminescent emissions of Dy(III) ion in the visible region.     

Densification and high-temperature oxidation behavior of SiC sintered with multicomponent rare-earth additives

This study examined the effects of rare-earth (RE) elements such as Sc, Y, Ce, and Yb on the densification and oxidation of SiC. After adding binary or ternary RE nitrates in liquid form to β-SiC, hot pressing was performed at 1750 °C for 2 h under 20 MPa. RE nitrate was transformed into RE oxide and formed a liquid phase during sintering by a reaction with SiO₂ present on the SiC surface, where the total amount of RE oxide was fixed at 5 wt%. RE-based silicate melts acted as sintering additives without decomposing SiC at high sintering temperatures. SiC containing Sc–Y as an additive showed a much higher density (≥ 99%) than SiC containing the conventional Al–Y additive (∼95%). The multicomponent RE additive with a melting point (T_m) < 1550 °C had a relatively lower density than that with a higher T_m, owing to the evaporation of the additive at 1750 °C. The density of SiC also depended on the additive composition. The oxidation test, conducted at 1300 °C for up to 168 h in air, exhibited a parabolic weight gain. The SiC sample sintered with the Sc–Yb additive achieved the highest resistance of 3.23 × 10⁻⁵ mg/cm⁴·s.     

Facile synthesis of silicon dioxide nanoparticles decorated multi-walled carbon nanotubes with graphitization and carboxylation for electrochemical detection of gallic acid

We proposed an efficient and scalable ultrasound-assisted approach for the synthesis of functionally integrated nanohybrid of silicon dioxide (SiO₂) nanoparticles and multi-walled carbon nanotubes with graphitization and carboxylation (GCMCN), which was employed to modify the glassy carbon electrode (GCE) for the fabrication of GCMCN@SiO₂/GCE sensor. Graphitization of GCMCN contributed to the reduction of defect density and enhancement of electrical conductivity, and carboxylation of GCMCN improved the dispersion degree of carbon nanomaterial due to the hydrophilicity of carboxyl groups. SiO₂ nanoparticles possessed abundant binding active sites for target analytes due to the surface hydroxyl groups or silanol groups, which were beneficial for the enrichment of gallic acid (GA) molecules. For the functionally integrated GCMCN@SiO₂ nanocomposite, the interconnected conductive networks of GCMCN presented more efficient charge transport channels, which recompensed the non-conductive property of SiO₂ nanoparticles. Based on the functional collaboration of GCMCN and SiO₂ nanoparticles, the fabricated GCMCN@SiO₂/GCE sensor presented good GA detection property (GA concentration: 0.01–15 μM, LOD value: 1.99 nM). The proposed sensor exhibited acceptable repeatability, reproducibility, and selectivity. Moreover, the good practicability performance could be effectuated at the GCMCN@SiO₂/GCE sensor for the quantitative analysis of GA in black tea and green tea samples.     

Composition Waves in Solution-Processed Organic Films and Its Propagations from Kinetically Frozen Surface Mesophases

Organic thin films deposited from solution attract wide interest for next-generation (opto-)electronic and energy applications. During solvent evaporation, the phase evolution dynamics for different components at different locations are not synchronic within the incrementally concentrated liquid films, determining the final anisotropic morphology and performance. Herein, by examining tens of widely investigated optoelectronic organic films, the general existence of composition wave propagating along the surface-normal direction upon solidification is identified. The composition wave is initiated by a few nanometers thick surface mesophase kinetically forming at the foremost stage of phase transition, and afterward propagates toward the substrate during solvent evaporation. The composition waves exhibit well-defined wave properties, including spatial wavelength, period, amplitude, and propagation velocity. These wave properties are closely correlated with the evaporation rate and the diffusion rate of organic molecules, which determines the dynamically varied local composition gradient along the surface-normal direction. Such composition waves are commonly found for more than 80% of randomly examined solution-processed thin films for high-performance organic electronic devices including photovoltaic cells and field-effect transistors.     

Achieving high comprehensive energy storage properties of BNT-based ceramics via multiscale regulation

It is difficult to obtain high polarization strength and high breakdown strength synchronously, resulting in the drawback of lower energy storage density, which inhibits commercial application of energy storage materials. We have successfully prepared (1-x)(0.93Bi_0.5Na_0.5TiO₃-0.07CaSnO₃)-xSrTiO₃ (BNT–CS–xST) ceramics by solid-state method. The presence of polymorphic nanodomains and the large electric displacement generated by the high charge Sr²⁺-Sr²⁺ ion pairs help to delay saturation polarization (P_m ∼ 48.64 μC/cm² at 315 kV/cm). In addition, the breakdown field strength (E_b) is increased by grain refinement and increasing the band gap. It is noteworthy that a high recoverable energy storage density (W_rec = 4.2 J/cm³) and a great efficiency (η = 88%) were achieved simultaneously in BNT–CS–0.5ST ceramic. Moreover, excellent charge-discharge performance was also achieved, with a discharge energy density W_d of 2.2 J/cm³, a current density C_D of 1724 A/cm² and a power density P_D of 250 MW/cm³. The study demonstrates that the great potential of BNT–CS–xST ceramics in power storage devices and provides an effective strategy for designing ceramics dielectric capacitors with excellent performance.