Silver sulfide is a narrow-band-gap semiconductor with high ionic conductivity and excellent chemical stability. Ag₂S nanoparticles exhibit size-tunable optical properties, including strong absorption in the near-infrared region, and low toxicity compared to other silver-based nanomaterials. They are widely explored for applications in infrared photodetectors, bioimaging, sensors, and solid-state ionic devices, as well as in thermoelectric and electronic switching systems.