The emerging metasurfaces with the exceptional capability of manipulating an arbitrary wavefront have revived the holography with unprecedented prospects. However, most of the reported metaholograms suffer from limited polarization controls for a restrained bandwidth in addition to their complicated meta-atom designs with spatially variant dimensions. Here, we demonstrate a new concept of vectorial holography based on diatomic metasurfaces consisting of metamolecules formed by two orthogonal meta-atoms. On the basis of a simply linear relationship between phase and polarization modulations with displacements and orientations of identical meta-atoms, active diffraction of multiple polarization states and reconstruction of holographic images are simultaneously achieved, which is robust against both incident angles and wavelengths. Leveraging this appealing feature, broadband vectorial holographic images with spatially varying polarization states and dual-way polarization switching functionalities have been demonstrated, suggesting a new route to achromatic diffractive elements, polarization optics, and ultrasecure anticounterfeiting.

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Carbon nanodots (C-dots) show great potential as an important material for biochemical sensing, energy conversion, photocatalysis, and optoelectronics because of their water solubility, chemical inertness, low toxicity, and photo- and electronic properties. Numerous methods have been proposed for the preparation of C-dots. However, complex procedures and strong acid treatments are often required, and the as-prepared C-dots tend to be of low quality, and in particular, have a low efficiency for photoluminescence. Herein, a facile and general strategy involving the electrochemical carbonization of low-molecular-weight alcohols is proposed. As precursors, the alcohols transited into carbon-containing particles after electrochemical carbonization under basic conditions. The resultant C-dots exhibit excellent excitation- and size-dependent fluorescence without the need for complicated purification and passivation procedures. The sizes of the as-prepared C-dots can be adjusted by varying the applied potential. High-quality C-dots are prepared successfully from different small molecular alcohols, suggesting that this research provides a new, highly universal method for the preparation of fluorescent C-dots. In addition, luminescence microscopy of the C-dots is demonstrated in human cancer cells. The results indicate that the as-prepared C-dots have low toxicity and can be used in imaging applications.

Phase, polarization, amplitude, and frequency represent the basic dimensions of light, playing crucial roles for both fundamental light-material interactions and all major optical applications. Metasurfaces have emerged as a compact platform to manipulate these knobs, but previous metasurfaces have limited flexibility to simultaneous control them. A multi-freedom metasurface that can simultaneously and independently modulate phase, polarization, and amplitude in an analytical form is introduced, and frequency multiplexing is further realized by a k-space engineering technique. The multi-freedom metasurface seamlessly combines geometric Pancharatnam-Berry phase and detour phase, both of which are frequency independent. As a result, it allows complex-amplitude vectorial hologram at various frequencies based on the same design strategy, without sophisticated nanostructure searching of massive geometric parameters. Based on this principle, full-color complexamplitude vectorial meta-holograms in the visible are experimentally demonstrated with a metal-insulator-metal architecture, unlocking the longsought full potential of advanced light field manipulation through ultrathin metasurfaces.functional layers, emerge as a desirable platform to manipulate the light field at will with large control and flexibility. [3][4][5][6][7] Exciting applications have already been demonstrated on the metasurface platform, including flat diffractive and polarization optical components, much more compact and lightweight than conventional bulky counterparts. By engineering the scattering properties of the individual metaelements constituting the metasurface to mold the geometric phase, resonant phase or propagation phase, we are able to control phase, [8,9] amplitude, [10,11] polarization, [12,13] or frequency [14][15][16] of light, leading to high-efficiency metalenses, [9] high-fidelity holograms, [8] broadband polarization components, [12,17] and highperformance biosensors. [15] However, these ultrathin components tend to focus on single-dimensional light manipulation, controlling either the local phase, or amplitude, or polarization, or frequency, at a time, inherently limiting potential opportunities. For example, metasurface holograms and metalenses based on resonant phase and propagation phase are typically limited to a narrow range of frequencies. [18,19] Geometric Pancharatnam-Berry (P-B) phase metasurfaces operate over broader bandwidths, but they are restricted to circular polarization only. [8] To improve the performance and enrich the functionality of metasurfaces for a broader range of applications, independent