Bi-tunable terahertz absorber based on strontium titanate and Dirac semimetal.

We proposed a polarization-insensitive absorber based on strontium titanate (STO) and bulk Dirac semimetal (BDS) in the terahertz (THz) region. The center frequency of the absorption peak can be independently regulated by temperature or Fermi energy level of STO or BDS, respectively. The numerical simulation result reveals that the peak absorptivity reaches to 99.98% at 2.16 THz when the temperature and Fermi energy were set at 300 K and 20 meV, respectively. Interestingly, by adjusting the temperature of STO from 250 to 400 K, the simulation results indicate that the center frequency can be tuned from 1.94 to 2.53 THz, and peak absorptivity can be maintained above 99% at normal incident. As the Fermi energy EF of Dirac semimetal increases from 10 to 60 meV, the center frequency can be changed from 2.14 to 2.44 THz and the amplitude of absorption peaks can be tuned from 99.9% to 82.8%. Impedance matching theory was used to understand the tunable performance. Furthermore, interference theory was employed to further explain the absorption mechanism of the proposed absorber. The absorber achieves bi-controlled absorptance via two independently controllable methods, which may provide guidance to research tunable, smart and multifunctional terahertz devices.

Comparison of Metabolites and Main Nutritional Components between Uncooked and Cooked Purple Rice.

Cooking can lead to varying degrees of nutrient loss in purple rice. For this investigation, two varieties of purple rice (YZN1 and YZ6) were chosen as the focal points to explore the metabolites associated with rice nutrition post cooking using nontargeted and targeted metabolomics techniques. The results showed that after cooking the two purple rice varieties, the contents of the flavonoids; OPC; TP; total antioxidant capacity; and K, Na, Fe, Mn, Zn, Cu, Ca, and Mg significantly decreased. Compared with YZN1U (YZN1 uncooked), the amino acid and mineral element contents in YZN1C (YZN1 cooked) decreased to varying degrees. After cooking YZ6, the contents of seven amino acids significantly decreased. Following the preparation of purple rice, the metabolites primarily engaged in the pathways of flavonoid synthesis and flavone and flavonol synthesis. Flavonoids, total antioxidant capacity, mineral elements, and amino acids showed a strong correlation with delphinidin and luteolin. The ROC analysis demonstrated that the value of the area under the curve for delphinidin and luteolin was 1 when comparing YZ6C (YZ6 cooked) and YZ6U (YZ6 uncooked), as well as YZN1C and YZN1U. Delphinidin and luteolin can be used as potential biomarkers of nutrient loss after cooking purple rice. This study holds significant implications for the balanced nutrition and healthy development of human dietary grains.

Intermediate excited state suppression and upconversion enhancement of Er3+ ions by carbon-doping boosting photocarrier separation in bismuth oxychloride nanosheets.

Low luminescence efficiency of rare-earth ions dopedupconversion (UC) nanomaterials is still a major limitation for their applications.Here, based on bismuth oxychloride nanosheets that show efficient photocarriers separation due to combining spontaneous polarization and layered semiconductor, we report a new carbon heterovalent doping strategy for efficient UC luminescence enhancement by suppressing the intermediate excited states of Er3+ ions. The first-principles calculations and photoelectrochemical characterizations provide evidences that the replacement of C ions for Cl strengthen the spontaneous polarization and inter electric field (IEF) of bismuth oxychloride nanosheets, which further improve the photocarriers separation efficiency. Under 808 or 980 nm excitation, the emission intensity of 4I13/2 energy level of Er3+ ions (1550 nm) increase slightly with C doping, but the its decay time and the visible UC emission are improved tremendously at the same time. We show that the recombination rate of intermediate excited state electrons of Er3+ ions with the ground state is inhibited by the enhanced IEF, which promotes the energy reabsorption transition to upper energy levels, thus enhancing the visible UC emission. This work not only may provide a new insight into the method for engineering of UC emissions but also deepen the understanding for layered semiconducting material to modify the transition of Lanthanide ions.

Surface Impedance of Metasurfaces/Graphene Hybrid Structures.

Understanding and manipulation of surface impedance in graphene hybrid structure is a significant issue for applications of graphene-based optoelectronics devices. In order to achieve this purpose in the terahertz region, analytical expressions for the impedances of metasurface were derived, which allows us to easily understand the relationship between physical dimensions and impedance. Simulation results show an excellent agreement with the analytical predictions. In addition, we focus on the synthetic impedance when square patch and graphene sheet joined together, discuss the influence of the size of metasurface as well as chemical potentiality as for graphene on the synthetic impedance. Based on these results, a number of absorbers as well as optical devices can be designed that utilize impedance metasurfaces.