The reliability of wide-bandgap (WBG) semiconductors used as power electronics is closely related to the high thermal conductivity of AlN-metalized substrates. Thus, the bonding of AlN ceramics with ...metals is a key issue for the production of reliable AlN-metalized substrates. This paper reports on a new method for producing AlN/Cu joints by employing a novel film metallization production process, which involves a porous network of Cu layer and Ag foil. The microstructure and the phases formed at the interface of the AlN/Cu joints produced at various brazing temperatures and times were analyzed by scanning electron microscopy and X-ray diffraction analysis. Strong joints with shear strength of 48.5 MPa were produced after brazing at 850 °C for 10 min. The typical microstructure at the interfacial reaction zone was Cu/Ag(s) + Cu(s)/CuAlO
2
+ Al
2
O
3
+ Cu(s)/AlN. The experimental results manifest the crucial role of the Ag–Cu eutectic liquid phase, formed by the reaction between the Cu layer and the Ag foil, and of the porous network of the Cu layer deposited on the surface of the AlN ceramic substrate, since both of them effectively favor the reduction in the residual thermal stresses in the joint and result in strong ceramic/metal joins.
Pure BaMgSiO4:Eu2+ phosphor, prepared by a solid state reaction method under N2 atmosphere, exhibited a strong green emission at 500 nm and a weak emission at 405 nm. Heat treatment under NH3 ...atmosphere causes changes in the PL intensity: the green emission at 500 nm gradually decreases and completely disappears after heat treatment for 3 h, whereas a new blue emission peak, centered at 445 nm, appears and becomes very strong. The results of the analyses with electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS) spectroscopy suggest that the heat treatment causes the generation of a large amount of oxygen vacancies. This resulted in the aforementioned color changes of the BaMgSiO4:Eu phosphor, which are confirmed by the results of DFT+U calculations. In particular, these calculations showed that Eu prefers to occupy Ba(3) sites, which are six coordinated to oxygen atoms. The emission at 500 nm was attributed to the 4f–5d transition energy of Eu in Ba(3) site, calculated as 2.54 eV. It was also shown that Eu 4f energy level decreases when oxygen is removed from the oxygen position adjacent to Eu, which results in a larger Eu 4f–5d transition energy and shorter wavelengths of emission peaks.
Red emitting Ba2Si(5-x)AlxN(8-x)Ox:Eu2+ phosphors were successfully produced by high-temperature solid state reaction method and their luminescence properties were experimentally measured. The ...analysis of the experimental results suggests that the partial substitution of Al-O for Si-N in the host lattice improves the photoluminescence properties and the thermal stability of the produced phosphors. The phosphors exhibited a broad red emission band between 500 and 750 nm. A red shift of emission peak from 588 to 624 nm was recorded with the increase of Al-O content, attributed to the enhancement of stokes shift. The excitation spectrum of the produced phosphors ranged between 200 and 600 nm, covering the UV and the blue region, and suggesting these materials as potentially suitable for use as conversion phosphors for white LED applications in the field of solid state lighting.
•Partial substitution of Al-O for Si-N improves the PL properties and the thermal stability.•A red shift of emission peak from 588 to 624 nm was recorded with the increase of Al-O content.•The red shift in the emission spectra attributed to the enhancement of stokes shift due to expansion of host lattice.•The PLE spectra of the produced phosphors ranged between 200 and 600 nm, covering the UV and the blue region.
The intrinsic problems of toxicity and instability of lead solar cells have motivated extensive research intended to develop alternative materials for photovoltaic applications. First-principles ...calculations were performed in order to shed light on replacing the Pb
2+
cation in lead- and mixed-halide materials with a formula of Cs
2
X
2
Y
2
(X, Y = F, Cl, Br, I). The calculated band gaps range from 0 eV to 3.188 eV, and the absorption coefficients from 6 to 16 × 10
4
cm
−1
. The band gap of Cs
2
Cl
2
I
2
is close to the Shockley-Queisser limit and its absorption coefficient is in the visible frequency range, which, in conjunction with its easy and economical synthesis process, qualify it as an alternative lead-free material for fabricating solar cells. It is suggested for further work that if the ratio of halogens is adjusted then the band gaps of Cs
2
F
2
Cl
2
, Cs
2
Cl
2
I
2
, Cs
2
Br
2
I
2
, and Cs
2
I
2
F
2
may be tuned to the desired electronic band gap limit required to improve their optoelectronic performance.
Phosphors of CaLa4Si3O13 singly- and co-doped with Ce3+ and Tb3+, which are suitable for application in white LEDs, were successfully produced by using a high temperature solid state reaction method. ...Their apatite crystalline structure as well as their photoluminescent properties both at room temperature and at higher temperatures (up to 150 °C) were experimentally determined, which also allowed the determination of the energy transfer efficiency and mechanism in the host lattice from the sensitizer Ce3+ ions to the activator Tb3+ ions. The excitation spectra of the doped phosphors exhibited an intense, broad band from 200 to 420 nm, which is a good match for the UV and near-UV chip (350–420 nm). Under excitation with UV light, two distinct luminescence bands were recorded; a blue one centered at 433 nm, which is typical for Ce3+ emission, and a green one, which peaks at 552 nm, originated from 5D4 → 7F5 transition in Tb3+.
•Both Ce3+ and Tb3+ ions occupy La3+ sites in CaLa4Si3O13 host.•The emission color shift from blue to green region in Ce3+/Tb3+ co – doped CaLa4Si3O13 phosphors.•The energy transfer efficiency is increase upto 93% with the increasing of Tb3+ concentration.•Energy transfer mechanism illustrate that dipole-dipole energy transfer are dominant from Ce3+ to Tb3+ ion.•The remaining intensity of green emission of Ce3+/Tb3+ co-doped CaLa4Si3O13 phosphors is 70% at 150 °C.
This study aims at evaluating the effect of simulating porcelain firing on the microstructure, corrosion behavior and mechanical properties of a Co–Cr–Mo alloy fabricated by Metal Soft Milling (MSM). ...Two groups of Co-28Cr-5Mo specimens (25 × 20 × 3 mm) were prepared by MSM: The as-sintered (AS) specimens and the post-fired (PF) specimens that were subjected to 5 simulating porcelain firing cycles without applying the ceramic mass onto their surface. Phase identification by X-ray Diffraction (XRD), microstructure examination by optical microscopy and Scanning Electron Microscopy combined with Energy-Dispersive X-ray Spectroscopy (SEM/EDX), corrosion testing by cyclic polarization and chronoamperometry in simulated body fluid (SBF), the latter test accompanied by Cr
3+
and Cr
6+
detection in the electrolyte through the 1.5-diphenylcarbazide (DPC) method and UV/visible spectrophotometry, and mechanical testing by micro-/nano-indentation were conducted to evaluate the effect of the post-firing cycles on the properties of Co–Cr–Mo. The results were statistically analyzed by the t test (p < 0.05: statistically significant). All specimens had a mixed γ-fcc and ε-hcp cobalt-based microstructure with a dispersion of pores filled with SiO
2
and a fine M
23
C
6
intergranular presence. PF led to an increase in the ε-Co content and slight grain coarsening. Both AS and PF alloys showed high resistance to general and localized corrosion, whereas neither Cr
6+
nor Cr
3+
were detected during the passivity-breakdown stage. PF improved the mechanical properties of the AS-alloy, especially the indentation modulus and true hardness (statistically significant differences: p = 0.0009 and 0.006, respectively). MSM and MSM/simulating-porcelain firing have been proven trustworthy fabrication methods of Co–Cr–Mo substrates for metal-ceramic prostheses. Moreover, the post-firing cycles improve the mechanical behavior of Co–Cr–Mo, which is vital under the dynamically changing loads in the oral cavity, whereas they do not degrade the corrosion performance.
Optical thermometry based on luminescence intensity ratio (LIR) is a hot topic in temperature sensing, due to fast response, high precision, the benefit of non-contact, etc. In this paper, the ...temperature-sensing capability of GdPO
4
:1%Dy
3+
phosphor was investigated through the approach of fluorescence intensity ratio based on the thermally coupled energy levels of Dy
3+
. The results show that the intensity of the emission, recorded under a 355 nm laser excitation, markedly increases with increasing temperature from 290 to 539 K. The LIR between the intensities of the emission of thermally coupled energy levels corresponding to
4
I
15/2
→
6
H
15/2
and
4
F
9/2
→
6
H
15/2
transitions monotonously increased with increasing temperature within the investigated temperature range. The maximum value of the relative sensitivity reaches the value of 1.55% K
−1
at 290 K, which is higher than the values reported in previous studies for similar phosphors. This finding suggests that the produced Dy
3+
-doped GdPO
4
phosphor is a promising candidate material for application in optical temperature sensing. Furthermore, the high relative sensitivity of 1.34% K
−1
was attained in the physiological temperature of the human body (310 K), which qualifies the produced phosphor for biological applications.
The current study addresses the problem of diseases transmitted from milk and dairy products to humans by bacteria. In the present study, CuO/Ag nanocomposites were synthesized, characterized, and ...tested for antibacterial activity. Sharp peaks at 2θ 37.38°, 44.04°, 64.31° and 77.27°, 32.29°, 38.28° and 46.36°, and 44.19°, 64.61° and 77.62° were observed in X-ray diffraction analysis, which correspond to the crystal planes of Ag, CuO and Ag–Cu, respectively. Scanning electron microscope image revealed the spherical shape of CuO/Ag nanopowders, with a size of 70 nm and crystallite size of 32 nm. The ultraviolet spectroscopy gave 2.25 and 2.06 eV bandgap energies for CuO and CuO/Ag, respectively. Furthermore, DFT calculations were performed in support of the experiment, and the structural change charge analysis and electronic band structures were analyzed. The antibacterial activity of CuO/Ag nanocomposites against
Escherichia coli
and
Staphylococcus aureus
was also evaluated using the Kirby–Bauer disk diffusion assay. Good antibacterial activity was observed against both milk bacteria with a sensitivity of 40–90% at CuO/Ag concentrations ranging from 6 to 200 mg/100 ml.
Microstructural and physico-mechanical characterization of highly translucent zirconia, prepared by milling technology (CAD-CAM) and repeated firing cycles, was the main aim of this
study.
Two groups ...of samples of two commercial highly-translucent yttria-stabilized dental zirconia, VITA YZ-HT
(Group A) and Zolid HT + White (Group B), with dimensions according to the ISO 6872 "Dentistry - Ceramic materials", were prepared. The specimens of each group were divided into two subgroups. The specimens of the first subgroups (Group A
and Group B
) were merely the sintered specimens. The specimens of the second subgroups (Group A
and Group B
) were subjected to 4 heat treatment cycles. The microstructural features (microstructure, density, grain size, crystalline phases, and crystallite size) and four mechanical properties (flexural strength, modulus of elasticity, Vickers hardness, and fracture toughness) of the subgroups (i.e. before and after heat treatment) were compared. The statistical significance between the subgroups (A
/A
, and B
/B
) was evaluated by the t-test. In all tests,
values smaller than 5% were considered statistically significant.
A homogenous microstructure, with no residual porosity and grains sized between 500 and 450 nm for group A and B, respectively, was observed. Crystalline yttria-stabilized tetragonal zirconia was exclusively registered in the X-ray diffractograms. The mechanical properties decreased after the heat treatment procedure, but the differences were not statistically significant.
The produced zirconia ceramic materials can be safely (i.e., according to the ISO 6872) used in extensive fixed prosthetic restorations, such as substructure ceramics for three-unit prostheses involving the molar restoration and substructure ceramics for prostheses involving four or more units. Consequently, milling technology is an effective manufacturing technology for producing zirconia substructures for dental fixed all-ceramic prosthetic restorations.
Developing an economical, durable, and efficient electrode that performs well at high current densities and is capable of satisfying large‐scale electrochemical hydrogen production is highly ...demanded. A self‐supported electrocatalytic “Pt‐like” WC porous electrode with open finger‐like holes is produced through industrial processes, and a tightly bonded nitrogen‐doped WC/W (WC‐N/W) heterostructure is formed in situ on the WC grains. The obtained WC‐N/W electrode manifests excellent durability and stability under multi‐step current density in the range of 30–1000 mA cm−2 for more than 220 h in both acidic and alkaline media. Although WC is three orders of magnitude cheaper than Pt, the produced electrode demonstrates comparable hydrogen evolution reaction performance to the Pt electrode at high current density. Density functional theory calculations attribute its superior performance to the electrode structure and the modulated electronic structure at the WC‐N/W interface.
Well established industrial processes are employed to produce self‐supported electrocatalytic WC porous electrode, which features open finger‐like holes and tightly bonded nitrogen‐doped WC/W heterostructure. The electrode manifests excellent stability under multi‐step current density in the range of 30–1000 mA cm−2 for more than 220 h in acidic and alkaline media.
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