Monolayer MoS2 (ML-MoS2) with various polymorphic phases attracts growing interests for device applications in recent years. Herein, a field-effect transistor (FET) gas sensor is developed on the basis of monolayer MoS2 with a heterophase of a 1T metallic phase and a 2H semiconducting phase. Lithium-exfoliated MoS2 nanosheets own a monolayer structure with rich active sites for gas adsorption. With thermal annealing from 50 to 300 °C, the initial lithium-exfoliated 1T-phase MoS2 gradually transforms into the 2H phase, during which the 1T and 2H heterophases can be modulated. The 1T/2H heterophase MoS2 shows p-type semiconducting properties and prominent adsorption capability for NO2 molecules. The highest response is observed for 100 °C annealed MoS2 of a 40% 1T phase and a 60% 2H phase, which shows a sensitivity up to 25% toward 2 ppm NO2 at room temperature in a very short time (10 s) and a lower limit of detection down to 25 ppb. This study demonstrates that the gas detection capability of ML-MoS2 could be boosted with the heterophase construction, which brings new insights into transition-metal dichalcogenide gas sensors.

Yb–Bi codoped phosphate glass was prepared and its properties were compared with Bi-doped phosphate glass. The broadband infrared luminescence intensity from Yb–Bi codoped glass was ∼32 times stronger than that of Bi-doped glass. The single-pass optical amplification was measured on a traditional two-wave mixing configuration. No optical amplification was observed in Bi-doped glass, while apparent broadband optical amplification between 1272 and 1336nm was observed from Yb–Bi codoped glass with 980nm laser diode excitation. The highest gain coefficient at 1272nm of Yb–Bi codoped glass reached to 2.62cm−1. Yb–Bi codoped phosphate glass is a promising material for broadband optical amplification.

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Bi-doped BaF 2 crystal was grown by the temperature gradient technique and its spectral properties were investigated. The absorption, emission and excitation spectra were measured at room temperature. Two broadband emissions centered at 1070 and 1500 nm were observed in Bi-doped BaF 2 crystal. This extraordinary luminescence should be ascribed to Bi-related centers at distinct sites. We suggest Bi 2+ or Bi + centers adjacent to F vacancy defects are the origins of the observed NIR emissions. References and links1. L. F. Johnson, R. E. Dietz, and H. J. Guggenheim, " Optical maser oscillation from Ni 2+ in MgF2 involving simultaneous emission of phonons," Phys. Rev. Lett. 11, 318-320 (1963

Spectral properties of Yb3+∕Ni2+ codoped transparent silicate glass ceramics containing LiGa5O8 nanocrystals were investigated. The near-infrared emission intensity of Ni2+ was largely increased with Yb3+ codoping due to Yb3+→Ni2+ energy transfer. The qualitative calculation of the energy transfer constant Cs-a and rate Ps-a showed that the Yb3+→Ni2+ energy transfer was much greater than in the opposite direction. Yb3+∕Ni2+ codoped glass ceramics with 0.75mol% Yb2O3 exhibited a near-infrared emission with full width at half maximum of 290nm and fluorescent lifetime of 920μs. The glass ceramics are promising for broadband optical amplification.

Nitride phosphor SrAlSi4N7:Eu2+ was synthesized by gas pressure sintering of powder mixtures of Sr3N2, AlN, α‐Si3N4, and EuN at 1750°C under 0.48 MPa N2. The photoluminescent properties of SrAlSi4N7:Eu2+ were measured and analyzed. Two‐peak emission from Eu2+ located at two different Sr sites in the SrAlSi4N7 host structure was observed. When the phorphors were excited at 410 nm, the highest emission intensity was found to be ∼126% of that in YAG:Ce3+ excited at 460 nm. The highest relative emission intensity at 150°C was ∼84.6% of that at 30°C. The highest external quantum efficiency acheived was 58.5%. SrAlSi4N7:Eu2+‐based phosphors are potential for white light‐emitting diodes.

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