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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