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Hybrid-excited generators have a wide voltage regulation capability or a wide range of variable-speed constant-voltage output capability, providing a significant advantage in the new energy power generation field. To achieve the optimal design of brushless hybrid excitation synchronous generators with third harmonic excitation, it is necessary to grasp the influence of design parameters on excitation power accurately. Firstly, this paper elaborates on the structure and principle of the hybrid excitation synchronous generator. From the perspective of excitation power generation, the expression for excitation power in hybrid excitation generators has been derived, identifying the primary factors influencing excitation power, which include winding parameters, structural parameters, and magnetic circuit saturation. Secondly, qualitatively calculate the influence of the number of turns and arrangement, turns in rotor harmonic, air gap length, and thickness of the permanent magnet on the excitation power, which is verified by the electromagnetic field finite element method. The results showed that the use of full pitch and a moderate increase in turns, a decrease in air gap length, and an increase in the thickness of the permanent magnet can all increase the rotor excitation power. A brushless hybrid excitation synchronous generator prototype based on third harmonic excitation was developed, the correctness of theoretical analysis and calculation were verified by test results. [ABSTRACT FROM AUTHOR]

Multicolor emission and dynamic color tuning with large spectral range are challenging to realize but critically important in many areas of technology and daily life, such as general lighting, display, multicolor detection and multi-band communication. Herein, we report an excitation-power-dependent color-tuning emission from an individual Sn-doped CdS nanowire with a large spectral range and continuous color tuning. Its photoluminescence (PL) spectrum shows a broad trap-state emission band out of Sn dopants, which is superposed by whispering-gallery (WG) microcavity due to the nanostructure size and its structure, besides the CdS band-edge emission. By simply changing the excitation power from 0.25 to 1.36 mW, we demonstrate that the typical Sn-doped CdS nanowire with the weight ratio of 10:1 of CdS and SnO2, the emission color can change from red to orange to yellow to green. In view of the stable properties and large spectral range, the Sn-doped CdS nanowires are very promising potential candidates in nanoscale optoelectronic devices. [ABSTRACT FROM AUTHOR]

Photoluminescent (PL) properties of undoped nanocrystals of cadmium sulfide were investigated as a function of excitation power intensity. Room-temperature PL spectra of CdS nanocrystals grown from the gas phase revealed two emission bands: with peak positions at 510 nm (near-band-edge emission) and close to 690 nm (deep trap defects). Tunable photoluminescence of CdS nanocrystals with the exchange of the main radiative channel from relaxation through defect levels to direct near-band-edge relaxation with the change of the color was demonstrated. Nonlinear behavior of the intensities of near-band-edge and defect level emission lines as well as the blue shift of the peak of defect level emission are discussed and explained by the finite capacitance of the defect subzone in the forbidden gap. The origin of the red-light emission is due to native defects such as sulfur vacancies or twinning interfaces. [ABSTRACT FROM AUTHOR]

Modulating the electronic properties of transition metal dichalcogenides (TMDCs) by oxygen plasma treatment has attracted great attention. However, the effect of excitation power on oxidation and etching process in oxygen plasma treatment still lacks systematic investigation. In this work, optical microscopy, Raman and photoluminescence spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy (XPS) are used to characterize the oxidation and etching behaviors of atomically thin MoS2 and WSe2 nanosheets treated by oxygen plasma with different excitation powers. The oxidation process is in a predominant position from 0 to 20 s, while etching is the dominant behavior from 30 to 120 s for monolayer (1L) to trilayer (3L) MoS2 and WSe2 nanosheets under low power plasma. However, etching is the apparent behavior of the MoS2 surface all through the middle and high power oxygen plasma. Similar etching was also found for WSe2 except for the first 10 s treatment under middle and high power. Interestingly, the top layer of bilayer (2L) and 3L WSe2 nanosheets can be oxidized to the WO3 layer homogeneously with height increased by ∼2 nm after 10 s treatment under optimal excitation power. In addition, thinning of the top layer MoS2 and WSe2 took the same time, while more time was taken for WSe2 to thin the following layer. Our results indicate that 1L and 2L MoS2 showed better stability than 1L and 2L WSe2, while the reverse situation was observed for 3L WSe2 under low power plasma. WSe2 was more stable than MoS2 under middle and high power plasma, which could originate from the different protection abilities between WO3 and MoO3. Our study might provide useful information for thinning and controlled formation of a surface oxide layer on TMDCs nanosheets, which is of great interest in modulating their electronic properties. [ABSTRACT FROM AUTHOR]

Abstract Er3+-doped and Er3+-Tm3+-co-doped transparent hexagonal NaGdF4 glass ceramics are fabricated via melt-quenching method. The emissions of Er3+-doped NaGdF4 glass ceramics are adjusted from the green to red by varying the concentration of Tm3+ ion under the excitation of 980 nm. The spectrum, thermal quenching ratio, fluorescence intensity ratios, and optical temperature sensitivity of the transparent glass ceramics are observed to be dependent on the pump power. The maximum value of relative sensitivity reaches 0.001 K−1 at 334 K in Er3+-doped NaGdF4, which shifts toward the lower temperature range by co-doping with Tm3+ ions, and has a maximum value of 0.00081 K−1 at 292 K. This work presents a method to improve the optical temperature behavior of Er3+-doped NaGdF4 glass ceramics. Moreover, the relative sensitivity SR is proved to be dependent on the pump power of 980-nm lasers in Er3+-doped NaGdF4 and Er3+-Tm3+-co-doped NaGdF4.

Triplet-level population distributions of organic molecules in glassy matrices were studied by computer simulation for various exciting-light intensities and compound concentrations. The dependence of the triplet-level population distribution on these variables was found. A consequence of the established relationship was that the exciting-light intensity affected the concentration dependence of the luminescence intensity where the population change of the molecular ground state resulting from their transition into the triplet state could not be neglected. [ABSTRACT FROM AUTHOR]

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• Fluorophosphate glasses doped withTb3+ and Eu3+. • Tuning the color of the emission via the excitation wavelength. • Excitation power control of the color of the emitted light. • Effect of tungsten on the PL of Tb3+ and Eu3+. We report in this work on the optical properties of a fluorophosphate glass system having the starting composition [60 (NaH 2 PO 3 , H 2 O) + 15 ZnO + 15 BaF 2 + 10 WO 3 ] prepared by the conventional melt-quenching procedure and doped with different concentrations of Tb3+ and Eu3+ ions. The XRD diffraction pattern has proved the amorphous nature of this glass system. The analysis of the optical spectra showed that Tb3+ ions may be excited by UV or blue light directly or through energy transfer from tungsten species, whereas Eu3+ ions may be excited by UV or blue radiations through charge transfer bands or sensitization by Tb3+ ions. We have shown that we can tune the color of the emitted light by changing either the doping concentration or the excitation wavelength. We have also seen that it is possible to tune the color of the emitted light by the same glass sample just by varying the excitation power, which is more convenient than modifying the doping concentration or the excitation wavelength and it may be important for the conception of solid-state lighting source. [ABSTRACT FROM AUTHOR]

Er-doped and Er-Tm-co-doped transparent hexagonal NaGdF glass ceramics are fabricated via melt-quenching method. The emissions of Er-doped NaGdF glass ceramics are adjusted from the green to red by varying the concentration of Tm ion under the excitation of 980 nm. The spectrum, thermal quenching ratio, fluorescence intensity ratios, and optical temperature sensitivity of the transparent glass ceramics are observed to be dependent on the pump power. The maximum value of relative sensitivity reaches 0.001 K at 334 K in Er-doped NaGdF, which shifts toward the lower temperature range by co-doping with Tm ions, and has a maximum value of 0.00081 K at 292 K. This work presents a method to improve the optical temperature behavior of Er-doped NaGdF glass ceramics. Moreover, the relative sensitivity S is proved to be dependent on the pump power of 980-nm lasers in Er-doped NaGdF and Er-Tm-co-doped NaGdF. [ABSTRACT FROM AUTHOR]

We report the thermal conductivities of monolayer (1L) and bilayer (2L) WS grown by chemical vapor deposition (CVD), which are determined by use of temperature and excitation dependences of E and A Raman modes. The first-order temperature coefficients of E and A modes in both supported and suspended WS layers were extracted. The frequency shift of the A mode with temperature is larger than that of the E mode for 1L-WS, which is attributed to stronger electron-phonon coupling for the A mode than that for the E mode. Moreover, by use of the shift of the phonon mode induced by laser heating, the thermal conductivities at room temperature were estimated to be 32 and 53 W/(m·K) for 1L- and 2L-WS, respectively. Our results provide fundamental information about the thermal properties of WS layers, which is crucial for developing applications of atomically-thin WS devices. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Analytical and experimental studies of a hybridised synchronous reluctance machine with a variable Xd/Xq ratio characteristic is the subject of this study. The machine comprises a round rotor and a salient pole machine element that is mechanically coupled together and integrally wound. There are two sets of poly‐phase windings in each stator. The windings of one of the sets are transposed between the two sections of the machine. Either set of the windings may be connected to the supply while the other feeds a balanced capacitance load. It is shown that by tuning of the capacitance load that the Xd/Xq ratio varies theoretically from zero to infinity at very good power factors. The machine characteristics were verified using the generalised two‐axis theory and validated by experimentation. The experimental and analytical results obtained show good agreement. Saturation was investigated by using the variation of the d‐axis inductance with machine loading. A set of rotor windings may be introduced for the purpose that the machine be self‐starting and self‐synchronising as a motor. The rotor field windings when fed with dc, will make the machine also capable of operation as a stand‐alone salient‐pole generator. For this purpose, it was shown that for a very high saliency ratio, reluctance power can be considerably higher than the excitation power. [ABSTRACT FROM AUTHOR]

Abstract: The excitation density dependent photoluminescence (PL) spectra in Ga1−x Mn x N layers (where x≈0.1–0.8%) grown on sapphire (0001) substrates using the plasma-enhanced molecular beam epitaxy technique have been investigated. The efficient PL peaks are observed in the red (1.86eV), yellow (2.34eV), and blue (3.29eV) spectral ranges. By examining the dependence of PL on the excitation laser power density at 15 and 300K, the yellow band (2.34eV) and bandgap (3.50eV) luminescence vary linearly with the light intensity, which are in good agreement with a simple recombination model, which assumes a density of recombination centers below the conduction band edge. [ABSTRACT FROM AUTHOR]

Abstract: Through a co-precipitation method Gd(OH)3: 0.5% Tm3+, 10% Yb3+ powder was synthesized. After sintering at different temperatures, the as-prepared Gd(OH)3: 0.5% Tm3+, 10% Yb3+ powder was changed into cubic and monoclinic phase Gd2O3: 0.5% Tm3+, 10% Yb3+ phosphors. Crystalline phases and morphologies of as-prepared powder and phosphors were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). Up-conversion (UC) fluorescence spectra of Gd2O3: 0.5% Tm3+, 10% Yb3+ phosphors were recorded by a fluorescence spectrophotometer with a 980nm continuous wave laser diode as the excitation source. Fluorescence decay behaviors of the phosphors were measured by exciting with 980nm from an optical parametric oscillator (OPO) pumped by a pulsed Nd: YAG laser with a pulse duration of 10ns and a repetition frequency of 10Hz, and the signal was recorded using a monochromator and an oscillograph. Phase and excitation power dependent UC fluorescence properties of the phosphors were studied in detail in the article. Interestingly, the cubic phase phosphors presented thermal optical bistability phenomena. The fluorescence dynamic analysis indicated that rise and decay processes existed in the phosphor UC fluorescence. [Copyright &y& Elsevier]

Abstract: The excitation-power dependence of the near-band-edge emission in ZnO inverse opals and nanocrystal films has been studied. The dependence of the photoluminescence intensity I on the excitation power L can be described by a power law, i.e., I∼L α , where α is an exponent that is often used to identify the origin of the near-band-edge emission from semiconductors in previous models. However, in this work, it was found that the values of α show a strong variation between ZnO inverse opals and nanocrystal films. And our results show that the change of α is mainly caused by the laser heating effects. Therefore, the value of α could not be simply employed to unequivocally evaluate the origin of the near-band-edge emission in complex nanostructures. [Copyright &y& Elsevier]

We have studied the effect of the intensity of the exciting radiation and the temperature on the emission properties of two kinds of thin-film samples based on blends of two types of organic electroactive materials: polyfluorene + iridium triphenylpyridinate and polyepoxypropylcarbazole + zero-th order PAMAM dendrimer with eosin. We have shown that an increase in the excitation intensity leads to an increase in the intensity of the luminescence of the polymer matrices and the iridium complex up to a power density of 300 kW/cm2, and the emission of the dendrimer is rapidly saturated and does not return to the initial value when the excitation level decreases. Heating up to 170°C followed by cooling causes an increase in the intensity for all the components except the dendrimer. The data obtained show that annealing is an important method for improving the emission efficiency of the proposed thin-film structures, due to a change in the packing of the activator molecules in the polymer matrix leading to more efficient transfer of the excitation energy. Molecules of the studied dendrimer are not stable when exposed to optical radiation and temperature. [ABSTRACT FROM AUTHOR]

The excitation power of a scattering body is governed, in general, by the forward-scattering theorem. In this paper, the theorem is reconfirmed by simply applying Poynting's theorem to a loaded transmission line. It is shown that the excitation power is determined by the interaction of the incident voltage with the forward-scattered current. For some special cases, the backward-scattering formula can yield the same result. A transmission line with a shunt load is one of the examples where the excitation power can be expressed as the real part of the product of the incident voltage and the conjugate of the backward-scattered current. In this work, an experiment has been performed to verify the above results. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate efficient light emission enhancement from Si with Er/O co-implanting coupled to 2-D hexagonal photonic crystal (PC) double-heterostructure microcavity fabricated on silicon-on-insulator. A single sharp resonant peak with 1552.2 nm communication wavelength dominates the photoluminescence (PL) spectrum and 35-fold PL intensity enhancement is obtained compared to the case of identically implanted silicon-on-insulator wafer at room temperature. The obvious red-shift and degraded Q-factor of resonant peak are present with the excitation power increasing, and the maximum measured Q-factor of 3829 is found at 1.5 mW power. The resonant peak is observed to shift depending on the structural parameters of PC. [ABSTRACT FROM PUBLISHER]