Far-From-Equilibrium Dynamics of Self-Trapped Excitons in the Wake of a Swift Ion

Due to its abundance, transparency, and chemical inertness, amorphous a-SiO₂ (silica) holds a special status as a key material in the history of human technology. Its tunable optical properties, electrical resistivity, and thermal resistivity have made it useful in contemporary technologies such as photonics, microelectronics, microelectromechanical systems, laser optics, and in the nuclear power industry. In several of these areas, silica is exposed to high-energy and/or high-intensity radiation. We are studying the complex physics of carrier generation, transport, exciton formation, and recombination that occurs in the wake of an energetic ion.<br/><br/>Ion irradiations of fused silica were performed at cryogenic temperatures from 30-100 K using light and heavy ions (3 MeV H, 3.5 MeV He, 19 MeV Si, and 10 MeV Cl). <i>In-situ </i>cryo-ionoluminescence was used to monitor the radiative recombination of self-trapped excitons (STEs) that rapidly form in a nanometer-sized region of high electronic excitation density produced by the passage of a swift ion. The light yield, its dependence on temperature, ion energy and mass, and its real-time kinetic evolution throughout the irradiation reveal details about the complex process of carrier generation, hopping, binding, and recombination. A parameter-free model was developed that quantitatively reproduces the experimentally observed light yield. The model helps us understand the competition between non-radiative Auger recombination, STE formation and dissociation, and carrier hopping. At lower electronic excitation densities, the light yield is primarily governed by the STE formation lifetime and Auger recombination rate. As the excitation density increases, thermal dissociation of STEs into self-trapped holes and electrons becomes more prominent and shifts the balance between radiative and non-radiative recombination.