Expanding the optical response of monolayer MoS2 into the infrared regime while achieving multi-band luminescence is a significant challenge. Herein, we systematically investigate the electronic and optical properties of Er-doped monolayer MoS2 by combining experimental characterizations with first-principles calculations based on density functional theory (DFT). The introduction of Er effectively extends the spectral range of MoS2 into the infrared/near-infrared (IR/NIR) region via characteristic Er3+ 4f-4f transitions, successfully realizing simultaneous up-conversion (UC) and down-conversion (DC) luminescence. Mechanistically, Er doping introduces localized impurity levels and lattice distortion that modulate the anisotropic dielectric function. This modulation enhances IR/NIR absorption, maintains visible transparency, and reduces VIS/UV reflectivity. Notably, the computed polarization-resolved absorption ratio, H(ω)=α//(ω)/α⊥(ω), exhibits a pronounced dependence on doping concentration, (H(ω) = 1.35 at 1.33% vs. 0.83 at 2.08%, evaluated at 1.15 eV). Such a magnitude of anisotropy is comparable to that reported for established anisotropic 2D materials. This work demonstrates that rare-earth ion doping is a robust strategy for tailoring the luminescence and optical properties of MoS2, paving the way for the fabrication of advanced MoS2-based optoelectronics, including highly sensitive NIR and polarization-sensitive photodetectors.
This paper proposes a compact four-band tunable terahertz metamaterial perfect absorber based on an AlCuFe quasicrystal for refractive index sensing. The absorber consists of a patterned AlCuFe quasicrystal resonant layer, a SiO2 dielectric spacer, and a continuous Au ground film. Full-wave simulations yield four narrow absorption peaks at 3.240, 3.564, 3.934, and 4.276 THz, with peak absorption values of 0.9944, 0.9950, 0.9916, and 0.9985, respectively. The absorption mechanism is interpreted using reflection suppression, electric-field localization, impedance matching, cavity resonance, and temporal coupled-mode theory. Increasing the AlCuFe Fermi level from 75 to 95 meV blueshifts all four peaks while preserving their spectral order. In the refractive-index sweep from n = 1.00 to 1.10, the sensitivities of F1-F4 are 1177, 1486, 1986, and 1800 GHz/RIU, respectively, and all four linear fits have R^2 values above 0.9995. F3 provides the highest sensitivity of 1986 GHz/RIU and the largest figure of merit of 26.79 RIU^-1. At normal incidence, the TE and TM spectra nearly coincide, and the four absorption bands remain stable when the polarization angle φ is varied from 0 to 90°. The proposed absorber is therefore polarization-insensitive under the normal-incidence condition used throughout this study.
Hybrid honeycomb-kagome silicene (hhk-silicene) exhibits excellent physicochemical properties and thus holds great promise for applications such as nanoscale field-effect transistors. Reducing its two-dimensional structure to one-dimensional nanoribbons (hhk-SiNRs) introduces edge states and quantum confinement effects, enabling dimensional control over the bandgap and carrier localization. On this basis, edge hydrogenation, as a chemical modification strategy, offers the potential to precisely tune the geometric structure and electronic properties of low-dimensional silicon-based materials. Herein, using the self-consistent charge density functional tight-binding (SCC-DFTB) method, we systematically investigate the effects of ribbon width, ranging from 2 to 10 periods, and edge hydrogenation on the structural stability and electronic properties of monolayer hhk-SiNRs. We find that, unlike other silicene-based nanomaterials, hhk-SiNRs exhibit only out-of-plane displacements after structural relaxation and edge hydrogenation, featuring significant spatial overlap. For pristine nanoribbons, the width is the key parameter governing structural stability and electronic properties: increasing the width effectively enhances the binding energy and narrows the bandgap, accompanied by charge ransfer from the right-hand semicircular edge to the left-hand triangular edge. Edge hydrogenation effectively reduces the edge buckling of pristine nanoribbons: hydrogen atoms on the left triangular edge induce a flat local arrangement and relieve stress, while those on the semicircular edge suppress upward buckling and induce a slight downward shift, thereby improving structural stability. Width plays a dominant role in bandgap engineering: for widths of 2 – 5 periods, hydrogenation opens the bandgap, enabling modulation in the range of 0.453 – 0.743 eV; for widths of 6 – 10 periods, hydrogenation closes the bandgap, and the electronic properties exhibit a continuous transition from semiconductor to semimetal to metal. The hydrogenation-induced charge transfer originates from the electronegativity difference associated with the Si–H bond, and pronounced electron transfer occurs in regions where the edges undergo severe distortion, with the extent of transfer further modulated by the nanoribbon width. The results demonstrate that edge hydrogenation can effectively modulate the electronic properties of hhk-SiNRs, providing a theoretical basis for further exploring their potential applications in nanoelectronic devices and offering valuable guidance for the design of high-performance silicon-based nanodevices in the post-Moore era.
