In this work, a multifunctional binder with self‐healing, flame retardant, high conductivity, and abundant polar groups is prepared by the free radical polymerization method and applied to lithium–sulfur (Li‐S) batteries to achieve high safety and exceptional electrochemical performance. The self‐healing characteristic of binder induced by intermolecular hydrogen bonds and SS dynamic covalent bonds can repair volume expansion cracks. The polar groups and excellent conductivity endue binder with strong chemisorption on polysulfides and fast charge transportation, which can effectively inhibit the shuttle effect and accelerate polysulfides redox kinetics. More important, the considerable flame retardant performance of binder can improve the safety of the LiS batteries. As a result, the LiS cells using FHCP binder deliver an outstanding cycle stability of a high‐capacity retention rate of 85% after 100 cycles at 0.2 C, and a high reversible area specific capacity of 5.25 mAh cm–2 at a sulfur loading of 4.72 mg cm–2 and a correspondingly lean electrolyte condition (E/S ratio = 6 µL mg–1).
In this paper, we investigate the temperature dependence of luminescence characteristics of highly efficient cerium-doped scintillator, lutetium-yttrium orthosilicate Lu2(1−x)Y2xSiO5:Ce3+. The photoluminescence excitation and emission spectra have been measured in a broad temperature range. The temperature dependence of the Ce1 and Ce2 decay times shows the onset of decay time decrease at about 300 K. This observation demonstrates that unlike so far reported, the Ce2 center is not substantially quenched until room temperature. The 5d1 excited-state ionization of both Ce1 and Ce2 centers is studied by purely optical methods.
The afterglow problem has been preventing CsI:Tl single crystal scintillators from being used for applications in the field of computer tomography and high-speed imaging. We show that Yb 2+ codoping in CsI:Tl can reduce it at least by one order of magnitude after 50 ms from X-ray cut-off compared to ordinary CsI:Tl. and higher effective atomic number (Z eff = 54) and allows the fabrication of micro-columnar films. Given its low cost, CsI:Tl materials became widely used for radiological imaging, 3 X-ray and gamma ray spectroscopy, homeland security and nuclear medicine applications. However, due to the persistent afterglow in CsI:Tl attributed to thermal ionization of trapped electrons (Tl 0 ) followed by radiative recombination with trapped holes [V KA (Tl + )], 4 which causes the pulse pile up in high count-rate applications, its usage in computer tomography (CT) and high-speed imaging applications is thus not possible.
5,6Thus, ways to suppress the afterglow in CsI:Tl have been researched intensively over the last two decades. In general, co-doping by an appropriate ion was found to be an effective method to suppress the afterglow in scintillators and phosphors as has been shown e.g. Therefore, despite the success of the afterglow suppression in CsI:Tl the codoping strategies mentioned above have simultaneously deteriorated the other important scintillation characteristics such as light yield and energy resolution which points to the complex character of the scintillation mechanism. Impurities (doped ions) may introduce energy levels in the band gap of the host crystal which interfere with the charge 3312 | CrystEngComm, 2014, 16, 3312-3317This journal is
GaN-based blue light emitting diodes (LEDs) have undergone great development in recent years, but the improvement of green LEDs is still in progress. Currently, the external quantum efficiency (EQE) of GaN-based green LEDs is typically 30%, which is much lower than that of top-level blue LEDs. The current challenge with regard to GaN-based green LEDs is to grow a high quality InGaN quantum well (QW) with low strain. Many techniques of improving efficiency are discussed, such as inserting AlGaN between the QW and the barrier, employing prestrained layers beneath the QW and growing semipolar QW. The recent progress of GaN-based green LEDs on Si substrate is also reported: high efficiency, high power green LEDs on Si substrate with 45.2% IQE at 35 A/cm2, and the relevant techniques are detailed.
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