Humidity sensors with high sensitivity, rapid response, and facile fabrication process for contactless sensing applications have received considerable attention in recent years. Herein, humidity sensors based on hexagonal boron nitride (h-BN) nanosheets that are synthesized by a facile ultrasonic process have been fabricated, which display an ultrahigh sensitivity of 28,384% at 85% relative humidity (RH), rapid response/recovery time (3.0/5.5 s), and long-term stability in a wide humidity detection range (11%–85% RH), superior to most of the reported humidity sensors. The high sensitivity can be ascribed to the massive hydrophilic functional groups absorbed on the h-BN nanosheet surface. Benefiting from the high humidity sensing performances, contactless Morse code messaging and human writing and speech recognition have been demonstrated. This work demonstrates the great potential of the high-performance h-BN nanosheet-based humidity sensors for future contactless sensing devices.

Piezochromic luminescent materials have shown great potential in advanced optoelectronic applications. However, most of luminescent materials usually undergo emission quenching under external stimuli. Herein, we demonstrate for the first time that the photoluminescence of carbon dots (CDs) confined within sodium hydroxide can be enhanced when high pressure is applied. They exhibit a 1.6-fold fluorescence enhancement compared with pristine CDs. Importantly, the enhanced fluorescence intensity can be retained after the release of pressure to ambient conditions. A combination of experimental analysis and theoretical simulations indicates that such an enhanced emission is mainly attributed to the strong confinement resulting from the sodium hydroxide matrix, which can separate the CDs spatially and restrict the nonradiative pathway. These results provide a rational strategy for manipulating the optical properties of CDs with enhanced and retainable photoluminescence (PL) performance, thus opening up a venue for designing luminescent CDs-based materials.