Two-Dimensional Semiconducting Boron Monolayers

The two-dimensional boron monolayers were reported to be metallic both in previous theoretical predictions and experimental observations, however, we have firstly found a family of boron monolayers with the novel semiconducting property as confirmed by the first-principles calculations with the quasi-particle G0W0 approach. We demonstrate that the vanished metallicity characterized by the pz-derived bands cross the Fermi level is attributed to the motif of a triple-hexagonal-vacancy, with which various semiconducting boron monolayers are designed to realize the band-gap engineering for the potential applications in electronic devices. The semiconducting boron monolayers in our predictions are expected to be synthesized on the proper substrates, due to the similar stabilities to the ones observed experimentally.Comment: 12 pages, 4 figure

A Practical Criterion for Screening Stable Boron Nanostructures

Due to the electron deficiency, boron clusters evolve strikingly with the increasing size as confirmed by experimentalists and theorists. However, it is still a challenge to propose a model potential to describe the stabilities of boron. On the basis of the 2c-2e and 3c-2e bond models, we have found the constraints for stable boron clusters, which can be used for determining the vacancy concentration and screening the candidates. Among numerous tubular structures and quasi-planar structures, we have verified that the stable clusters with lower formation energies bounded by the constraints, indicating the competition of tubular and planar structures. Notably, we have found a tubular cluster of B₇₆ which is more stable than the B₈₀ cage. We show that the vacancies, as well as the edge, are necessary for the 2c-2e bonds, which will stabilize the boron nanostructures. Therefore, the quasi-planar and tubular boron nanostructures could be as stable as the cages, which have no edge atoms. Our finding has shed light on understanding the complicated electron distributions of boron clusters and enhancing the efficiency of searching stable B nanostructures

Competition between Pauli Exclusion and H‑Bonding: H₂O and NH₃ on Silicene

We demonstrate that the competition between Pauli exclusion and H-bonding dominates the adsorption of H₂O on silicene through first-principles calculations. It explains the bewildering problem that isolated H₂O is inert on silicene while isolated NH₃ tends to chemisorption. Moreover, Pauli exclusion can be overcome by the synergetic effect of Si···O dative bonding and intermolecular H-bonding. As a result, H₂O molecules are readily to chemisorb in clusters. It is expected that the competition is in general polar molecule adsorption on silicene and, thus, crucial for the adsorption mechanism

Highly Efficient and Stable Narrow-Band Red Phosphor Cs₂SiF₆:Mn⁴⁺ for High-Power Warm White LED Applications

Due to the unique narrow-band red emission and broadband blue light excitation, as well as milder synthesis conditions, Mn⁴⁺ ion activated fluoride red phosphors show great promise for white light emitting diode (W-LED) applications. However, as the Mn⁴⁺ emission belongs to a spin-forbidden transition (²E_g → ⁴A₂), it is a fundamental challenge to synthesize these phosphors with a high external quantum efficiency (EQE) above 60%. Herein, a highly efficient and thermally stable red fluoride phosphor, Cs₂SiF₆:Mn⁴⁺, with a high internal quantum efficiency (IQE) of 89% and ultrahigh EQE of 71% is demonstrated. Furthermore, nearly 95% of the room-temperature IQE and EQE are maintained at 150 °C. The static and dynamic spectral measurements, as well as density functional theory (DFT) calculations, show that the excellent performance of Cs₂SiF₆:Mn⁴⁺ is due to the Mn⁴⁺ ions being evenly distributed in the host lattice Cs₂SiF₆. By employing Cs₂SiF₆:Mn⁴⁺ as a red light component, stable 10 W high-power warm W-LEDs with a luminous efficiency of ∼110 lm/W could be obtained. These findings indicate that red phosphor Cs₂SiF₆:Mn⁴⁺ may be a highly suitable candidate for fabricating high-performance high-power warm white LEDs