The gain characteristics of Er3+/Yb3+-codoped phosphate fiber amplifier pumped with light of 980nm wavelength are theoretically studied in this paper. With the help of rate equations and the propagation equation of Er3+/Yb3+-codoped phosphate fiber, we analyzed the effects of concentration of erbium and ytterbium ions, pump power, signal power and fiber length on the gain characteristics of the co-doped fiber amplifier. Comparison with singly erbium-doped fiber amplifier was also made. It is shown that the sensitization of Yb3+ decreases the clustering effect of erbium ions in the fiber and the gain and pump efficiency of Er3+/Yb3+ co-doped fiber are apparently higher than that of singly erbium-doped fiber. Numerical results also demonstrate that considerable signal gain of 10dB can be achieved in a 3.2cm-long fiber amplifier with 20dBm(100mW) pumping power at 980 nm.
Z_scan experiments are performed on the azobenzene polymer (DR_13_PMMA) films with He_Ne laser. It is found that the relation between the cha nge of refractive index of the sample and the light intensity behaves like a sat u rable effect, whose relative parameters are alterable with light intensity. It i s also found that the change of refractive index induced by linearly polarized l ight is distinctly greater than that induced by circularly polarized light. The phenomena are explained by using the theory based on the effect of angular hole burning of photoisomerization.
7 new phosphorous heterocycle compounds have been studied by XPS and MS. From XPS and MS data we have discussed the existence form and manner of the compounds isomer, and verified that the isomer only exists in gaseous state and liquid state.
The influence of 12 nm spherical silver nanoparticles (AgNPs) and 20 nm spherical gold nanoparticles (AuNPs) on the luminescence of europium complex Eu(TTFA)3 were studied. When 350 nm is chosen as the incident light, the maximum enhancement factor of the complexes mixed with AgNPs is about 2.5 at the wavelength of 612 nm. Besides the enhancement of the localized field, the overlap between the localized surface plasmon resonance spectra of nanoparticles and the absorption band of fluorescent molecules is another important factor for excitation field enhancement. By means of the quasi-static approximation theory, the distribution of the electric field around a single spherical metallic nanopaticle illuminated by plane wave was calculated. The simulation results show that the field enhancement effect is more obvious when the incident light is close to the resonance of the metallic nanoparticle, which could be demonstrated by our following experimental results. The distribution of the electric field under the same conditions was also simulated through the COMSOL software. The results are consistent with those of the quasi-static approximation theory.
Abstract The reactor is very critical to intensify the reaction rate controlled by mass transfer. Solid magnesium hydride (MgH 2 ) shows great advantages in hydrogen storage; however, poor liquid–solid hydrolysis kinetics limit its application. Various chemical reactors were explored and are used to improve the hydrolysis efficiency. Results show that the mixing style could affect the surface coating behavior. Specifically, the higher temperature and mixing strength could promote the MgH 2 hydrolysis. Furthermore, induced crystallization could effectively relieve coating and strengthen the hydrolysis, especially at the high mixing level. The result indicated that the mass transfer distance between crystal seed and formed MgH 2 particles played an important role in MgH 2 hydrolysis.
Upconversion fluorescence in Nd:YVO4 crystal under a laser diode (LD) pump was investigated. It is proved that the predominant mechanism for excitation of 4G7/2 level is an energy transfer upconversion. Then,a theoretical approach to upconversion effect on LD pumped Nd:YVO4 laser is given.In addition,the role of upconversion in thermal effect is discussed in detail.
The efficient production of γ-valerolactone (GVL) from renewable lignocellulose that is synthesized in plants by photosynthesis to replace the declining fossil resources conforms to the principles of circular economy. Compared to direct hydrogenation by H2 molecules, catalytic transfer hydrogenation (CTH) of levulinic acid (LA) and/or its esters to GVL with organic alcohols as a hydrogen source is a much milder route. The synergistic catalysis between Lewis and Brønsted acids is indispensable in the CTH process. Considering that unsaturated coordinated Zr species could act as Lewis acid sites and phosphotungstic acid (PTA) could dissociate protons as Brønsted acid sites, UiO-66 (Zr) was thus "acidified" by encapsulating PTA in its channels to tune the ratio of Brønsted to Lewis acid sites as a bifunctional catalyst so as to better understand the catalytic structure-performance relationship in the CTH process. To address the dilemma of encapsulated PTA that is prone to leach, a rapid surface sealing strategy was adopted to establish a polyimide (PI) coating over the surface of UiO-66 introducing a space confinement effect via an anhydride-amine coupling reaction. The as-synthesized PTA/UiO-66@PI catalyst exhibited 100% of LA conversion, a 93.2% of GVL yield and high recyclability for at least five consecutive cycles. Moreover, a reaction pathway followed by esterification, hydrogenation and dealcoholization as well as a catalytic hydrogenation mechanism based on intermolecular hydride β-H transfer were proposed. Current work not only provides a high-performance and high-stability catalytic system to selectively produce GVL from LA or its esters, but also sheds light on the catalytic mechanism of the CTH process at the molecular level.
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