Light‐Induced Precipitation of an Inorganic Phosphate for Direct Writing of Thin Films and Templating Complex Mineral Morphologies

Light-induced direct patterning allows intricate spatiotemporal control over microscopic structures and has even been extended to functional inorganic materials. However, while sol–gel-based materials such as silica maintain structural continuity, photoinduced precipitation of salts such as carbonates and phosphates typically suffers from a granular nature and produces loose particle assemblies. In this study, UV-induced release of phosphoric acid from an organic precursor is exploited for locally modulating supersaturation levels. This allows for controlled interplay between photogeneration and precursor supply, for the precipitation of structurally continuous, non-granular barium phosphate from solution. Based on these insights, nanoscopic thin films with controllable thickness are deposited in an illuminated spot. By moving the light beam, this approach is extended to direct writing based on user-defined patterns. Moreover, by triggering photoinduced mineralization within organic templates, complex morphologies can be replicated with high fidelity. This versatility and precision will open new opportunities for the design of functional, biologically relevant inorganic materials.