Luminescent compounds obtained from the thermal reaction of citric acid and urea have been studied and utilized in different applications in the past few years. The identified reaction products range...

replace toxic, expensive, or conflict materials with environmentally and socially more benign CNMs. Therefore, they are still considered promising candidates for a range of future applications in electronics, optoelectronics, or catalytic systems. Laser-fabrication methods have been investigated as fast, energy-saving, low-cost, and precise material processing techniques in both science and industry and even a new "age of photon-driven materials manufacturing" has been prognosed. [5] In industry, laser-processing techniques are mainly used for cutting, welding, cladding, or surface processing. [6] It allows for high-precision materials modifications with unprecedented accuracy, not only spatially but also temporally, which is of particular interest for the manufacturing of future small-scale electronic and photonic products. Also direct laser-induced materials synthesis has become an active field of research. For example, laser-induced ablation of graphite, discovered in the 1990s, is commonly used for the targeted synthesis of CNMs. [7,8] Highpower laser pulses hit a graphite target and create a carbon plasma above the surface, which reacts to crystalline nanocarbons. These laser-assisted synthesis methods differ from conventional thermal methods in the reaction timescales. Heat transfer within micro-or milliseconds allows for reactions different to conventional heating methods. Moreover, the precise spatial control with nano-to micrometer resolutions allows also for the fine patterning of materials. Generally, laser-patterning describes the micro-structuring of organic materials like polymers or plastics by evaporating material from their surface. [9] Directed 2D-film patterning by laser-induced material conversion evolved in the past years as a new synthetic fabrication method. [10] In particular, the uncomplicated access to laser-assisted patterning of graphene oxide and their relatives has given the field a significant push. [11-18] In most cases, graphene is produced by laser-induced reduction of graphene oxide (GO). Another famous laser-patternable material is polyimide (PI), which carbonizes at high temperatures. [19-21] Vast research efforts have been conducted on the characterization and application of laser-patterned GO or PI films. [22-24] However, the starting materials used are rather expensive and the modification of the resulting materials properties is limited since the starting materials are polymeric. Other materials could be used as precursor like paper or wood but without the possibility of choosing the initial substrate. [25] A precursor ink for carbon laser-patterning is developed using inexpensive, naturally abundant molecular compounds, namely citric acid and urea, and used to fine-print conductive carbon circuits on a flexible substrate. The precursor in the ink consists of organic nanoparticles obtained from the thermal treatment of citric acid and urea. This precursor is thoroughly characterized chemically and structurally. A simple recipe for the ink is then described for the creation...

The design of inorganic nanoparticles relies strongly on the knowledge from solid-state chemistry not only for characterization techniques, but also and primarily for choosing the systems that will yield the desired properties. The range of inorganic solids reported and studied as nanoparticles is however strikingly narrow when compared to the solid-state chemistry portfolio of bulk materials. Efforts to enlarge the collection of inorganic particles are becoming increasingly important for three reasons. First, they can yield materials more performing than current ones for a range of fields including biomedicine, optics, catalysis, and energy. Second, looking outside the box of common compositions is a way to target original properties or to discover genuinely new behaviors. The third reason lies in the path followed to reach these novel nano-objects: exploration and setup of new synthetic approaches. Indeed, willingness to access original nanoparticles faces a synthetic challenge: how to reach nanoparticles of solids that originally belong to the realm of solid-state chemistry and its typical protocols at high temperature? To answer this question, alternative reaction pathways must be sought, which may in turn provide tracks for new, untargeted materials. The corresponding strategies require limiting particle growth by confinement at high temperatures or by decreasing the synthesis temperature. Both approaches, especially the latter, provide a nice playground to discover metastable solids never reported before. The aim of this Account is to raise attention to the topic of the design of new inorganic nanoparticles. To do so, we take the perspective of our own work in the field, by first describing synthetic challenges and how they are addressed by current protocols. We then use our achievements to highlight the possibilities offered by new nanomaterials and to introduce synthetic approaches that are not in the focus of recent literature but hold, in our opinion, great promise. We will span methods of low temperature "chimie douce" aqueous synthesis coupled to microwave heating, sol-gel chemistry and processing coupled to solid state reactions, and then molten salt synthesis. These protocols pave the way to metastable low valence oxyhydroxides, vanadates, perovskite oxides, boron carbon nitrides, and metal borides, all obtained at the nanoscale with structural and morphological features differing from "usual" nanomaterials. These nano-objects show original properties, from sensing, thermoelectricity, charge and spin transports, photoluminescence, and catalysis, which require advanced characterization of surface states. We then identify future trends of synthetic methodologies that will merit further attention in this burgeoning field, by emphasizing the importance of unveiling reaction mechanisms and coupling experiments with modeling.