Investigations of Photoluminescence Properties of CaxMg2-xSi2O6:yEu2+ (x = 0.5-1.25, y = 0.015-0.035) Phosphors.

Previously, there were almost no relevant studies on developing the optimal CaxMg2-xSi2O6:yEu2+ phosphor composition for its finest optical properties. This study employs two steps to determine the optimal composition for CaxMg2-xSi2O6:yEu2+ phosphors. First, CaMgSi2O6:yEu2+ (y = 0.015, 0.020, 0.025, 0.030, 0.035) was used as the primary composition of specimens synthesised in a reducing atmosphere of 95% N2 + 5% H2 to investigate the effect of Eu2+ ions on the photoluminescence properties of each variant. The emission intensities of the entire photoluminescence excitation (PLE) and photoluminescence (PL) emission spectra of the CaMgSi2O6:yEu2+ phosphors initially increased as the concentration of the Eu2+ ions increased, peaking at y = 0.025. The cause of the variations across the entire PLE and PL spectra of all five CaMgSi2O6:yEu2+ phosphors was investigated. Because the CaMgSi2O6:0.025Eu2+ phosphor had the highest PLE and PL emission intensities, in the next step, CaxMg2-xSi2O6:0.025Eu2+ (x = 0.5, 0.75, 1.0, 1.25) was used as the primary composition to investigate the effect on the photoluminescence properties when the CaO content varied. We also show that the Ca content has an apparent effect on the photoluminescence properties of CaxMg2-xSi2O6:0.025Eu2+ phosphors, and the optimal phosphor composition is Ca0.75Mg1.25Si2O6:0.025Eu2+ because it has the largest PLE and PL values. X-ray diffraction (XRD) analyses of CaxMg2-xSi2O6:0.025Eu2+ phosphors were performed to identify the factors responsible for this outcome.

Fabrication of high-power piezoelectric transformers using lead-free ceramics for application in electronic ballasts.

CuO is doped into (Na(0.5)K(0.5))NbO(3) (NKN) ceramics to improve the piezoelectric properties and thus obtain a piezoelectric transformer (PT) with high output power. In X-ray diffraction patterns, the diffraction angles of the CuO-doped NKN ceramics shift to lower values because of an expansion of the lattice volume, thus inducing oxygen vacancies and enhancing the mechanical quality factor. A homogeneous microstructure is obtained when NKN is subjected to CuO doping, leading to improved electrical properties. PTs with different electrode areas are fabricated using the CuO-doped NKN ceramics. Considering the efficiency, voltage gain, and temperature rise of PTs at a load resistance of 1 kΩ, PTs with an electrode with an inner diameter of 15 mm are combined with the circuit design for driving a 13-W T5 fluorescent lamp. A temperature rise of 6°C and a total efficiency of 82.4% (PT and circuit) are obtained using the present PTs.

Effects of improved process for CuO-doped NKN lead-free ceramics on high-power piezoelectric transformers.

In this paper, the effects of the electrical proper- ties of CuO-doped (Na(0.5)K(0.5))NbO(3) (NKN) ceramics prepared separately using the B-site oxide precursor method (BO method) and conventional mixed-oxide method (MO method) on high-power piezoelectric transformers (PTs) were investigated. The performances of PTs made with these two substrates were compared. Experimental results showed that the output power and temperature stability of PTs could be enhanced because of the lower resonant impedance of the ceramics prepared using the BO method. In addition, the output power of PTs was more affected by the resonant impedance than by the mechanical quality factor (Q(m)) of the ceramics. The PTs fabricated with ceramics prepared using the BO method showed a high efficiency of more than 94% and a maximum output power of 8.98 W (power density: 18.3 W/cm(3)) with temperature increase of 3°C under the optimum load resistance (5 kΩ) and an input voltage of 150 V(pp). This output power of the lead-free disk-type PTs is the best reported so far.

The influences of particle sizes on the dielectric properties of PEI/(Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 composites.

In order to investigate the embedded capacitors with higher capacitance value in the future, two technologies of increasing the dielectric constant of filler and decreasing the thickness of capacitors can be combined to develop a best method. For that, the high dielectric constant of (Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 (BSTZ) ceramic powders with three different sizes (3 microm, 200 nm, and 100 nm) are used as the filler to mix with polyetherimide (PEI) to form the PEI/BSTZ composites. The dielectric constants and loss tangents of PEI/BSTZ composites with different contents of BSTZ ceramic powders are measured using the plate method. As the contents of BSTZ powders increase from 10 wt% to 70 wt%, the dielectric constants and loss tangents of PEI/BSTZ composites increase with the increase content of BSTZ ceramic powders, independent on the particle sizes. As the BSTZ content is less than and equal to 50 wt% and same loading ratio is used, the dielectric constants of PEI/200 nm-BSTZ and PEI/100 nm-BSTZ composites are large than those of PEI/3 microm-BSTZ composites. In this study, the Lichtenecker logarithmic mixing rule is also used to fit the measured results and predict the dielectric constants of PEI/BSTZ composites.