The pH Value Control of Morphology and Luminescence Properties of Gd2O2S: Tb3+ Phosphors

Developing rare-earth doped oxysulfide phosphors with diverse morphologies has significant value in many research fields such as in displays, medical diagnosis, and information storage. All of the time, phosphors with spherical morphology have been developed in most of the related literatures. Herein, by simply adjusting the pH values of the reaction solution, Gd2O2S:Tb3+ phosphors with various morphologies (sphere-like, sheet-like, cuboid-like, flat square-like, rod-like) were synthesized. The XRD patterns showed that phosphors with all morphologies are pure hexagonal phase of Gd2O2S. The atomic resolution structural analysis by transmission electron microscopy revealed the crystal growth model of the phosphors with different morphology. With the morphological change, the band gap energy of Gd2O2S:Tb3+ crystal changed from 3.76 eV to 4.28 eV, followed by different luminescence performance. The samples with sphere-like and cuboid-like microstructures exhibit stronger cathodoluminescence intensity than commercial product by comparison. Moreover, luminescence of Gd2O2S:Tb3+ phosphors have different emission performance excited by UV light radiation and an electron beam, which when excited by UV light is biased towards yellow, and while excited by an electron beam is biased towards cyan. This finding provides a simple but effective method to achieve rare-earth doped oxysulfide phosphors with diversified and tunable luminescence properties through morphology control.

Epitaxial Growth and Optical Properties of Laser Deposited CdS Thin Films

In this study, cadmium Sulfide (CdS) thin films were synthesized on quartz substrates using an infrared pulsed laser deposition (IR-PLD) technique under high vacuum (~10−6 Torr) conditions. X-ray diffraction was used to evaluate the structural features. According to X-ray analysis, the deposited CdS films are crystalline and have a favored orientation on a plane (110) of an orthorhombic. The peak intensity and the average crystallite size increases with increasing the film thickness. After annealing at 300 °C, the orthorhombic phase transformed into a predominant hexagonal phase and the same result was obtained by SEM photographs as well. Spectrophotometric measurements of transmittance and reflectance of the CdS films were used to derive optical constants (n, k, and absorption coefficient α). The optical band gap energy was found to be 2.44 eV. The plasma plume formation and expansion during the film deposition have also been discussed. The photocurrent response as a function of the incident photon energy E (eV) at different bias voltages for different samples of thicknesses (85, 180, 220 and 340 nm) have been studied, indicating that the photocurrent increases by increasing both the film thickness and photon energy with a peak in the vicinity of the band edge. Thus, the prepared CdS films are promising for application in optoelectronic field.

Influence of Cr-doping on structural, magnetic and dielectric properties of M-type hexaferrites synthesized using microwave digestion technique

M-type hexaferrite SrCrxFe12-xO19 compounds doped with Cr (x=0, 1, 2, 3 and 4 at.%) were prepared by microwave digestion system. X-ray diffraction was used to study the structure and crystallization of the samples. The samples are found to have a hexagonal phase, SrFe12O19, as a main phase at 2Θ ≈ 33.144° and 35.618° for x = 0 and 1 respectively, and 32.451° and 34.295° for x ≥ 2. The Rietveld refined parameters such as the lattice parameters (a=b, c), direct and indirect cell volume, crystallite size and microstrain were investigated. TEM and SEM results showed that the samples have hexagonal shape and grain sizes range from 126 nm to 379 nm. Magnetization, M, as a function of the applied magnetic field, H, was obtained from the hysteresis loop. The coercive field, HC , saturation, Ms and remnant, Mr , magnetization and squareness ration, Mr/Ms , were extracted from the hysteresis loop results. These results revealed that HC is inversely proportional with the grains size of the samples but directly proportional with Cr-doping values candidating these compounds to be used in computer hard disk memories applications. M values are inversely proportional with Cr-doping values. The variation of conductivity, σ, impedance, Z, dielectric constant, ε, dielectric loss factor, tan δ and dissipation factor as functions of both AC frequency, F(Hz) and Cr-doping, x, were investigated. The maximum value of the dissipation factor was at x=2 which equals 8.05x109 m/F when F = 2x105 Hz. The impedance of the samples behaved as a capacitor reactance that makes our compounds candidate for many crucial dielectric applications.

Structure diagram and dynamics of formation of hexagonal boron nitride in phase-field crystal model

The phase-field crystal (PFC-model) is a powerful tool for modelling of the crystallization in colloidal and metallic systems. In the present work, the modified hyperbolic phase-field crystal model for binary systems is presented. This model takes into account slow and fast dynamics of moving interfaces for both concentration and relative atomic number density (which were taken as order parameters). The model also includes specific mobilities for each dynamical field and correlated noise terms. The dynamics of chemical segregation with origination of mixed pseudo-hexagonal binary phase (the so-called ‘triangle phase’) is used as a benchmark in two spatial dimensions for the developing model. Using the free energy functional and specific lattice vectors for hexagonal crystal, the structure diagram of co-existence of liquid and three-dimensional hexagonal phase for the binary PFC-model was carried out. Parameters of the crystal lattice correspond to the hexagonal boron nitride (BN) crystal, the values of which have been taken from the literature. The paper shows the qualitative agreement between the developed structure diagram of the PFC model and the previously known equilibrium diagram for BN constructed using thermodynamic functions. This article is part of the theme issue ‘Transport phenomena in complex systems (part 2)’.

Cubic versus Hexagonal – Phase, Size and Morphology Effects on the Photoluminescence Quantum Yield of NaGdF4:Er3+/Yb3+ Upconverting Nanoparticles

Upconverting nanoparticles (UCNPs) are well-known for their capacity to convert near-infrared light into UV/visible light, benefitting various applications where light triggering is required. At the nanoscale, loss of luminescence intensity...

Tuning The Properties of Ba-M Hexaferrite BaFe11.5Co0.5O19: A Road Towards Diverse Applications

The development of hexaferrite nanoparticles is scrutinized as potential sorbents for the removal of chromium (Cr) ions from aqueous chromium-containing solutions in a batch adsorption experiment. The transition metal Co doped BaFe12O19 hexaferrite compounds (BHF) have been synthesized successfully via citrate auto combustion technique. Structural, morphological, and magnetic properties are testified. X-ray diffraction pattern ratifies the existence of hexagonal phase as a main phase for the prepared samples. The average crystallite sizes are found in the range of 47–49 nm. The high-resolution transmission electron microscopy (HRTEM), as well as the Fourier, transform infrared spectrophotometry results confirm an M-type hexagonal structure existing. The c-T indicates the temperature-dependent ferromagnetic behavior of BHF nanoparticles. The derivative shows a single transition temperature Tc at 698 °C, 710 for BHF and BHCF respectively. The prepared samples are utilized as an adsorbent for the removal of Cr (VI) from the aqueous solution. The maximum adsorption capacity (qm) of Cr (VI) on the nano hexaferrite is higher than that of various other adsorbents testified in the literature. The pseudo-second-order kinetic model gives a better fit to the experimental data

Structural, Physical, and Mechanical Analysis of ZnO and TiO2 Nanoparticle-Reinforced Self-Adhesive Coating Restorative Material

This study aimed to modify an EQUIA coat (EC; GC, Japan) by incorporating 1 and 2 wt.% of zinc oxide (ZnO; EC-Z1 and EC-Z2) and titanium dioxide (TiO2; EC-T1 and EC-T2) nanoparticles, whereby structural and phase analyses were assessed using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), respectively. Thermogravimetric analysis/differential scanning calorimetry, micro-hardness, and water absorption analyses were conducted, and the microstructure was studied by scanning electron microscopy/energy-dispersive spectroscopy. FTIR spectra showed a reduction in peak heights of amide (1521 cm−1) and carbonyl (1716 cm−1) groups. XRD showed peaks of ZnO (2θ~31.3°, 34.0°, 35.8°, 47.1°, 56.2°, 62.5°, 67.6°, and 68.7°) and TiO2 (2θ~25.3°, 37.8°, 47.9, 54.5°, 62.8°, 69.5°, and 75.1°) corresponding to a hexagonal phase with a wurtzite structure and an anatase phase, respectively. Thermal stability was improved in newly modified materials in comparison to the control group. The sequence of obtained glass transitions was EC-T2 (111 °C), EC-T1 (102 °C), EC-Z2 (98 °C), EC-Z1 (92 °C), and EC-C (90 °C). EC-T2 and EC-T1 showed the highest (43.76 ± 2.78) and lowest (29.58 ± 3.2) micro-hardness values. EC showed the maximum water absorption (1.6%) at day 7 followed by EC-T1 (0.82%) and EC-Z1 (0.61%). These results suggest that EC with ZnO and TiO2 nanoparticles has the potential to be used clinically as a coating material.

Impact of CNT Concentrations on Structural, Morphological and Optical Properties of ZnO: CNT Nano composite Films

In this study, zinc oxide: carbon nanotube (ZnO: CNT) nano composite films with varying CNT concentrations (0,3,5,10, and 15) wt percent were generated utilizing the pulsed laser deposition (PLD) procedure on clean glass substrates at room temperature. The impact of CNT concentration on the structural, morphological, and optical features of ZnO: CNT nano thin films as deposited was examined. X-ray diffraction was used to evaluate the structure of the generated ZnO: CNT thin films, while an atomic force microscope was used to explore the morphological features of the nano films (AFM) and field emission scan electron microscopy (FESEM). The optical properties of prepared thin films were characterized and studied using UV-VIS-NIR spectrophotometer. The structures of prepared ZnO: CNT with different concentration of CNT thin films were polycrystalline. ZnO: CNT nano thin films were synthesized in hexagonal phase and the dominate orientation is (101). The crystallite sizes are 32 and 26 nm for (101) and (100)) planes for ZnO and ZnO: 15% CNT nano films respectively. These crystallite size are decreased with increasing CNT (0, 3,5,10 and 15) wt. %. The lowest grain size can be shown for ZnO, while the largest grain size can be seen in ZnO: CNT nano thin with 15% concentration, whereas FESEM micrographs displayed a typically rough, pronounced microstructure, with surface protrusions. The energy gap (Eg) of ZnO: CNT nano thin film with various concentrations is computed. The result analysis shows that Eg decreased with increasing CNT weight concentration. This type of behaviors make the prepared films are good candidate for broad range of applications such as optoelectronic and display devices.