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The marriage of traditional gas-sensing semiconductors with low dimensional nanostructures is expected to exhibit interesting properties in the detection of hazardous gases. Herein, novel hollow-spherical heterojunctions are assembled for thin film gas sensors by using p-type black phosphorus (BP) and n-type tin oxide (SnO 2). Green synthesis strategies are employed to prepare BP nanodots and SnO 2 quantum dots. The aerosol-assisted chemical vapor deposition is used to prepare thin films with hollow-spherical heterojunctions. The BP incorporation significantly improves the gas-sensing properties of SnO 2 -based thin films, which demonstrate excellent response and repeatability to H 2 S at room temperature. The BP-SnO 2 heterojunction demonstrates more than twice the response and sensitivity of pristine SnO 2 thin film. Moreover, the recovery ability is significantly improved and LOD is decreased to 50 ppb. The hollow-spherical heterojunction has a joint gas-sensing mechanism contributed by both of SnO 2 and BP. The SnO 2 provides fundamental receptor function for gas detection while incorporated BP facilitates the adsorption of target H 2 S and provides additional electrons through the p-n junction tunnel. In addition, a slight negative dependence on humidity is observed for the gas sensor. It is ascribed to the competitive adsorption of water molecules on the BP-SnO 2 heterojunction surface against H 2 S molecules and chemisorbed oxygen. This work not only proposes novel heterojunction nanostructures for room-temperature gas detection, but also contributes to the functional integration of traditional gas-sensitive materials and emerging 2D materials in sensor technology. [ABSTRACT FROM AUTHOR]

In recent years, lanthanide doped materials have been extensively studied in the field of fluorescence temperature sensing due to their abundant emission levels and sensitive thermal response. Temperature sensing based on fluorescence intensity ratio (FIR) of upconversion nanoparticles has the advantages of fast temperature response, non-aggressiveness, and high spatial resolution. However, the most reported FIR sensing has limited sensitivity, probably due to the use of thermal coupling levels. Herein, we report a novel FIR temperature measurement based on non-thermal coupling levels of NaGdF 4 :Yb3+/Er3+@NaGdF 4 @NaGdF 4 :Yb3+/Tm3+ core-shell-shell nanostructure, which has high sensitivity and robustness simultaneously. The relative sensitivity based on I 801 / I 654 and I 801 / I 841 of Tm3+ to Er3+ can reach up to 4.56 (303 K) and 3.82% K−1 (313 K), respectively. Between them, FIR of I 801 / I 841 is independent of excitation power and time. These results show the great potential of FIR based on non-thermal coupling levels in high-sensitive and robust temperature sensors. [ABSTRACT FROM AUTHOR]