In the RhB Degradation part of the Experimental Section, the concentration of RhB used in the experiments was incorrectly reported. The concentration is hereby corrected to read 10 −5 M. The text should thus read: "The experiments were performed at ambient temperature and pressure using Xe lamp, 175 W (Lambda). The concentration of RhB in all solutions was C 0 = 10 −5 M." The main conclusions are unaffected and the experiments will still work at the lower concentration. The authors apologize for any inconvenience caused.

Nanoporous metallic networks are a group of porous materials made of solid metals with suboptical wavelength sizes of both particles and voids. They are characterized by unique optical properties, as well as high surface area and permeability of guest materials. As such, they attract a great focus as novel materials for photonics, catalysis, sensing, and renewable energy. Their properties together with the ability for scaling-up evoke an increased interest also in the industrial field. Here, fabrication techniques of large-scale metallic networks are discussed, and their interesting optical properties as well as their applications are considered. In particular, the focus is on disordered systems, which may facilitate the fabrication technique, yet, endow the three-dimensional (3D) network with distinct optical properties. These metallic networks bridge the nanoworld into the macroscopic world, and therefore pave the way to the fabrication of innovative materials with unique optoelectronic properties.

The synthesis of rhenium‐doped fullerene‐like MoS2 nanoparticles (Re:IF‐MoS2) is described. Careful inductively coupled plasma mass spectrometry analysis reveals that the concentration of the rhenium atoms in the IF‐MoS2 lattice is more than 10‐fold smaller than the weighted amount of this atom in the precursor powder. High resolution scanning transmission electron microscopy in high angle annular dark field mode is used to decipher the isolated rhenium atoms in the MoS2 lattice and confirm that these atoms substitute for molybdenum atoms. Scanning electron microscopy analysis shows that, in contrast to the undoped nanoparticles which tend to agglomerate, the Re:IF‐MoS2 nanoparticles self‐assemble on substrate surfaces forming an ordered tessellated monolayer. Theoretical quantum‐chemical calculations show that the Re level is some 180 meV below the conduction band. Furthermore, the rhenium electrons are fairly localized in the MoS2 lattice. At a higher concentration the rhenium atoms form a mini‐band below the conduction band which coincides with the Fermi level of the lattice.

Nanoporous metallic networks are endowed with the distinctive optical properties of strong field enhancement and spatial localization, raising the necessity to map the optical eigenmodes with high spatial resolution. In this work, we used cathodoluminescence (CL) to map the local electric fields of a three-dimensional (3D) silver network made of nanosized ligaments and holes over a broad spectral range. A multitude of neighboring hotspots at different frequencies and intensities are observed at subwavelength distances over the network. In contrast to well-defined plasmonic structures, the hotspots do not necessarily correlate with the network morphology, emphasizing the complexity and energy dissipation through the network. In addition, we show that the inherent connectivity of the networked structure plays a key optical role because a ligament with a single connected linker shows localized modes whereas an octopus-like ligament with multiple connections permits energy propagation through the network.

Second harmonic generation (SHG) is forbidden from most bulk metals, because metals are characterized by a net zero electric-field in equilibrium. This limit breaks down when reaching nanoscale dimensions, as have been shown for metallic nano-particles and nano-cavities. Yet, nonlinear response from a three-dimensional (3D) macroscale metallic piece comprising suboptical wavelength features remains a challenge for many years. Herein, we introduce a largescale nanoporous metallic network whose building-blocks are assembled into an effective nonlinear conductive material, with a considerable conversion efficiency in a wide range of optical wavelengths. The high nonlinear response results from the network structure having a large surface area on which the inversion symmetry is broken. In addition, because of the 3D structure, hotspots can be formed also in deeper focal plans of the metallic network, and thus can give rise to coherent addition of the signal. The solid connectivity between the nanoscale building-blocks also plays a role, because it forms a robust network which may respond in a collective manner to form very intense hot-spots. Broadband responses of the metallic network are observed both by SHG and cathodoluminescence (CL). The large-scale dimension and generation of randomized hotspots make this 3D metallic network a promising candidate for applications like photocatalysis, sensing, or in optical imaging as structured illumination microscopy.