Light-Stimulated Luminescence Control of Lead Halide-Based Perovskite Nanocrystals Coupled with Photochromic Molecules via Electron and Energy Transfer.

Photoswitchable nanomaterials are key materials in the development of advanced imaging techniques, such as super-resolution fluorescence microscopy. The combination of perovskite CsPbBr3 nanocrystals (NCs) with bright photoluminescence (PL) emission and diarylethenes (DAEs) with structural changes in response to ultraviolet (UV) and visible light is a promising candidate system. Herein, CsPbBr3 NCs are coupled with photochromic DAE molecules to control the PL emission from the NCs by light stimulation. The PL emission is successfully switched ON and OFF by alternating UV and visible light irradiation. Time-resolved PL emission studies suggest that Förster resonance energy transfer from CsPbBr3 NCs to the closed-ring form of DAE occurs after UV irradiation, and the PL emission is quenched. Upon visible-light irradiation, DAE is converted to the open-ring isomer, and the PL emission is restored. Femtosecond pump-probe spectroscopy reveals that light stimulation induces not only energy transfer but also photoinduced electron transfer in the NC-DAE pair on the picosecond timescale to form DAE radicals. Thus, it is suggested that the holes residing in the NCs react with the NCs, degrading the PL emission. Stable PL switching is realized using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) as a hole scavenger to avoid the reaction between the holes and NCs.

Reversible ON/OFF switching of photoluminescence from CsPbX3 quantum dots coated with silica using photochromic diarylethene.

Highly luminescent silica-coated CsPbX3 quantum dots (QDs) with good photostability were synthesized and coupled with photochromic diarylethene to modulate the QDs' photoluminescence (PL). Upon successive UV and visible light irradiation, the PL emission from the silica-coated CsPbX3 QDs was repeatedly quenched and restored, demonstrating the promising feasibility of the QD/diarylethene-based photoswitches.

Synthesis of Cu2O/CuO Nanocrystals and Their Application to H2S Sensing.

Semiconducting metal oxide nanocrystals are an important class of materials that have versatile applications because of their useful properties and high stability. Here, we developed a simple route to synthesize nanocrystals (NCs) of copper oxides such as Cu2O and CuO using a hot-soap method, and applied them to H2S sensing. Cu2O NCs were synthesized by simply heating a copper precursor in oleylamine in the presence of diol at 160 °C under an Ar flow. X-ray diffractometry (XRD), dynamic light scattering (DLS), and transmission electron microscopy (TEM) results indicated the formation of monodispersed Cu2O NCs having approximately 5 nm in crystallite size and 12 nm in colloidal size. The conversion of the Cu2O NCs to CuO NCs was undertaken by straightforward air oxidation at room temperature, as confirmed by XRD and UV-vis analyses. A thin film Cu2O NC sensor fabricated by spin coating showed responses to H2S in dilute concentrations (1⁻8 ppm) at 50⁻150 °C, but the stability was poor because of the formation of metallic Cu2S in a H2S atmosphere. We found that Pd loading improved the stability of the sensor response. The Pd-loaded Cu2O NC sensor exhibited reproducible responses to H2S at 200 °C. Based on the gas sensing mechanism, it is suggested that Pd loading facilitates the reaction of adsorbed oxygen with H2S and suppresses the irreversible formation of Cu2S.