An emerging prospect of solution-processed organic–inorganic hybrid halide perovskites is promising for next generation x-ray imaging applications. Herein, the optical and x-ray scintillation properties of lead-free two-dimensional perovskite crystals are reported, i.e. X2MnCl4 (X = PEA, PPA). At room temperature (RT), the photoluminescence (PL) spectra of both crystals show a peak around 600 nm with the lifetime between 3 and 4 µs, making them applicable for scintillator in x-ray imaging applications. Materials with a small electronic band gap of about 2 eV may allow a good promise for high-light-yield scintillators. On the other hand, x-ray luminescence (XL) measurements for both crystals show no spectra at RT, while those at 10 K exhibit the similar features observed in PL spectra. Temperature-dependent XL intensities reveal thermal quenching behaviour with activation energies between 40 and 54 meV. Thermoluminescence (TL) and glow curves in both crystals show residual luminescence background as slow as 1648 s and some deep traps with energies as large as 190 meV. Thermal quenching and TL measurements of both crystals are the opposite of those of PEA2PbCl4 crystals. Although some properties may not be beneficial for scintillators, the small differences of scintillation properties in both crystals may provide direction for the new designs of high-light-yield lead-free perovskite single crystal scintillators.

The second harmonic generation (SHG) response was measured for arbitrarily oriented linear input polarization on Si(111) surfaces in rotational anisotropy experiments. We show for the first time, using the simplified bond hyperpolarizability model (SBHM), that the observed angular shifts of the nonlinear peaks and symmetry features—related to changes in the input polarization—help to identify the corresponding interface dipolar and bulk quadrupolar SHG sources, yielding excellent agreement with the experiment. Additionally, we evaluate for the s-in/p-out (sp) and p-in/p-out (pp)-polarization SHG intensities the contributions from the individual Si bonds. Furthermore, a relation between the four parameters arising from SBHM and six coefficients of the phenomenological SHG theory needed to reproduce experimental data is established.

No abstract

The aqueous sodium-ion battery is a promising alternative to the well-known lithium-ion battery owing to the large abundance of sodium ion resources. Although it is safer than the lithium-ion battery, the voltage window of the sodium-ion battery is narrower than that of the lithium-ion battery, thus limiting its practical implementation. Therefore, a highly concentrated electrolyte is required to address this issue. In the present work, the effect of the salt concentration on the transport properties of water molecules is investigated via theoretical analyses at the quantum mechanical level. A molecular dynamics simulation at the quantum mechanical level revealed that as the salt concentration increases, the ion–water interactions became stronger, leading to a lower diffusivity and a lower electronic band gap. These imply that the superconcentrated aqueous-based electrolytes have high potentials for the sodium-ion battery applications.