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.
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.
The internal electric field (IEF) of layered Bi-based semiconductors contributes to improving the bulk-charge separation (BCS) in the photocatalysis, attracting great attention for improving the catalytic activity of photocatalysts....
The sensitivity of optical temperature sensing based on the conventional rare-earth ion doped upconversion (UC) materials is limited by the energy gap between thermally coupled levels (TCLs) of rare-earth ions. Therefore, it is of great theoretical and technical interest to explore UC luminescent materials for optical temperature sensing with ultra-sensitive temperature characteristic. In this work, the UC luminescence properties and temperature sensing characteristics were studied for Er 3+ single-doped BiOCl excited by 1550 nm laser. Under near-infrared (NIR) excitation, BiOCl:Er 3+ exhibits strong red emission at 670 nm, weak green emissions at 525 and 542 nm, extremely weak violet emission at 406 nm, and near-infrared emission at 983 nm. Red and green emissions of the UC system exhibit strong temperature dependence, and in the temperature range of 300-563 K, the maximum absolute sensitivity (S A) obtained by employing the non-thermally coupled levels (NTCLs, 4 F 9/2 / 4 S 3/2) is 95.3×10-3 K −1 , which is 21 times more than that obtained by employing the thermally coupled levels (TCLs, 2 H 11/2 / 4 S 3/2), and the maximum relative sensitivity (S R) is as high as 1.19% K −1. The results show that the intense red UC luminescence and temperature sensing with ultra-high 第 8 期 彭跃红, 等: 1550 nm 激发层状 BiOCl:Er 3+ 上转换发光及温度传感特性 903 sensitivity in BiOCl:Er 3+ under 1550 nm excitation may have potential application prospect in display and optical temperature sensing.
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