Herein, a novel type of environment-sensitive carbon dots (ES-CDs) has been synthesized via ethanothermal reaction using 1,6-naphthalenediol as a carbon source and sulfuric acid as a catalyst. The morphology and structure of ES-CDs are characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectra (XPS). ES-CDs exhibit green and excitation wavelength independent emission in different solvents. Using the optical response of ES-CDs towards acetone-water binary mixtures with different composition, the sensitive detection of solvent polarity is realized based on the inner filter effect (IFE). The inkjet printed patterns of ES-CDs show a blue-to-green conversion as exposure to external vapor from hydrogen chloride to ammonia, and enable information to hide assisting with a laser direct writing. We believe that the environment-sensitive carbon dots developed in this study are potential candidates for solvent sensing and fluorescence anti-counterfeiting.

Optical physical unclonable functions (PUFs) have great potentials in the security identification of Internet of Things. In this work, electrospun nanofibers are proposed as a candidate for a nanoscale, robust, stable and scalable PUF. The dark-field reflectance images of the polymer fibers are quantitatively analyzed by Hough transform. We find that the fiber length and orientation distribution reach an optimal point as the fiber density grows up over 850 in 400 x 400 pixels for a polyvinylpyrrolidone nanofiber based PUF device. Subsequently, we test the robustness and randomness of the PUF pattern by using the fiber amount as an encoding feature, generating a reconstruction success rate over 80% and simultaneously an entropy of 260 bits within a mean size of 4 cm2. A scale-invariant algorithm is adopted to identify the uniqueness of each pattern on a 256-sensor device. Furthermore, thermo-, moisture as well as photostability of the authentication process are systematically investigated by comparing polyacrylonitrile to polyvinylpyrrolidone system.

Carbon dots (CDs) have great potentials in quantum emitters due to their simple synthesis, low cost, high stability, and tunable band gap; however, the low solid-state emission efficiency, as well as nanosecond-scale radiative lifetime, limits their applications requiring bright and fast emission. Here, a bright and ultrafast emission of red-emissive carbon dots (R-CDs) with narrow bandwidth (<30 nm) is achieved at room temperature by coupling with a plasmonic nanopatch antenna (NPA). The NPA manufacturing combines a conventional spin-coating process with a conformal transfer-print thin film technology, providing a widely applicable nanocavity for field enhancement with uniform quality in centimeter scale and accurate control of the position of emitters. The effective NPA−CD coupling generates an increase in the emission intensity of a factor of 76 and a shortened radiative lifetime of 80 ps, which demonstrates an 82-fold faster rate than the emission rate of uncoupled R-CDs. The NPA structure also shows striking enhancement of Raman spectra of carbon dots with an enhancement factor over 10 5 . These results may benefit the low-cost and large-scale fabrication of plasmonic cavity and enable carbon dots to find applications in quantum optics, from lowthreshold nanolaser to single-photon source.