Excessive exposure to ultraviolet (UV) rays in sunlight is harmful to human skin. The development of an intelligent UV monitor that can detect the solar UV intensity in real time is highly desirable for human health and safety. In this work, a sunlight-responsive paper-based color-switching film (PCSF) is developed by combining color-switchable titania/hydrated tungsten oxide (THTO) heteronanoparticles with a sticker paper substrate. The THTO heteronanoparticles with an average size of 10 nm are distributed tightly on the surface of the paper substrate. Owing to the advantages of the excellent sensitivity and selectivity to solar UV radiation of THTO heteronanoparticles and the high flexibility of the paper substrate, the PCSF shows great potential for solar UV radiation monitors. With the solar UV intensity increasing from 0.75 to 3.25 mW•cm −2 , the color of PCSF changes from colorless to blue and even dark blue. Moreover, the color change of the PCSF under solar UV irradiation featuring 40 s is calibrated to indicate the solar UV radiation intensity. Taking the advantage of the excellent sensitivity and selectivity to solar UV radiation, high reversibility, flexibility, and low cost, we further demonstrate the application of the PCSF as a reusable wristband for smart solar UV radiation monitors. This work provides a way for solar UV radiation monitors that could provide naked-eye monitoring of real-time personal solar UV radiation.

Organic-inorganic metal-halide materials (OIMMs) with zero-dimensional (0D) structures offer useful optical properties with a wide range of applications. However, successful examples of 0D structural OIMMs with well-defined optical performance at the micro-/nanometer scale are limited. We prepared one-dimensional (1D) (DTA) 2 SbCl 5 •DTAC (DTAC = dodecyl trimethyl ammonium chloride) single-crystal microrods and 2D microplates with a 0D structure in which individual (SbCl 5 ) 2À quadrangular units are completely isolated and surrounded by the organic cation DTA + . The organic molecular unit with a long alkyl chain (C 12 ) and three methyl groups enables microrod and -plate formation. The singlecrystal microrods/-plates exhibit a broadband orange emission peak at 610 nm with a photoluminescence quantum yield (PLQY) of ca. 90 % and a large Stokes shift of 260 nm under photoexcitation. The broad emission originates from selftrapping excitons. Spatially resolved PL spectra confirm that these microrods exhibit an optical waveguide effect with a low loss coefficient (0.0019 dB mm À1 ) during propagation, and linear polarized photoemission with a polarization contrast (0.57).Organic-inorganic metal-halide materials (OIMMs), a bulk crystal with 0D structure at the molecular level, have attracted tremendous attentions due to their potential optoelectronic applications as light-emitting materials. [1] These materials though in bulk; but can have bright emission and also retain as high as near unity photoluminescence quantum yield (PLQY). [2] Among different applications these could also serve as a potential optical materials in micro-/ nanosized optical waveguides. [3] To date, research on optical

Light-responsive rewritable paper (LRP) based on photochromic materials has attracted extensive attention to alleviating the problems of environmental sustainability, energy saving, and forest conservation. However, the development of LRP with long legible time of information and high reusable time still remains a great challenge for practical applications. Herein, an LRP with long legible time is fabricated based on photochromic phosphomolybdic acid (PMoA) composite nanoparticles by integrating photoreductive TiO 2 nanoparticles with redox-driven color-switchable PMoA clusters. The TiO 2 /PMoA composite nanoparticles with close interfacial contact are obtained through the electrostatic interaction between positively charged TiO 2 nanoparticles and negatively charged PMoA clusters, which ensures the highly efficient photoreversible color switching properties. Owing to the slow oxidation kinetics of reduced PMoA and excellent photochromic properties of TiO 2 /PMoA composite nanoparticles, LRP exhibits longawaited properties, such as long legible time of printed information (≥60 days), fast coloration time (≤50 s), on-demand erasing time (from 1.75 to 90 min), high reusable times (≥70 cycles), and positive imaging mode. As LRP is easy for large-scale production by a simple dip-coating method, we believe that LRP has great opportunities for practical applications in long-term temporary information reading and recording purposes.