Optoionics—A New Opportunity for Ionic Conduction-Based Radiation Detection

We recently demonstrated the ability to use photogenerated charge carriers to modulate the grain boundary resistance of a model polycrystalline oxygen solid electrolyte thin film (Gd-doped CeO₂)[i]. These findings were inspired by the recognition that above bandgap light is well known to reduce band bending at interfaces by providing additional charge carriers which screen potential barriers. While our initial observations were limited to thin films due to short absorption depths of above bandgap light, we then demonstrated that the same concept is applicable using gamma radiation, characterized by much deeper penetration depths than UV (nm vs. mm)[ii]. We showed that we could reproduce similar optoionic effects in a bulk ceramic of Gd-doped CeO₂ (1mm thick) and that reversible resistance modulation on the order of ~10³ near room temperature could be obtained. In this presentation, we discuss how our findings demonstrate new radiation detection device concepts that rely on modulation of ionic currents at grain boundaries in solid electrolytes rather than the collection of photogenerated charges carriers in single crystalline semiconductors. This paves the way for new, inexpensive, low-power, and miniaturizable solid-state detection devices that can operate in harsh environments. We will discuss our approaches for engineering impedance, radiation sensitivity and response time with the aim of achieving high-performance detection. This phenomenon is yet another example of the rapidly developing field of <i>Opto-ionics,</i> allowing for contactless triggering of ionic conduction in solids, and is expected to apply to other classes of ion-conducting solid electrolytes (Li⁺ or H⁺), thus paving the way to a broad new class of radiation detecting materials.<br/><br/>The authors acknowledge support by the U.S. Department of Homeland Security, Countering Weapons of Mass Destruction Office, under awarded grant 22CWDARI00046. This support does not constitute an express or implied endorsement on the part of the Government.<br/><br/><br/>[i] T. Defferriere, D. Klotz, J. C. Gonzalez-Rosillo, J. L. M. Rupp, and H. L. Tuller, <i>Photo-Enhanced Ionic Conductivity Across Grain Boundaries in Polycrystalline Ceramics</i><i>,</i> Nat. Mater. 21, 438-444 (2022) https://doi.org/10.1038/s41563-021-01181-2<br/><br/>[ii] T. Defferriere, A. S. H. A. Elwakeil, J. Rupp, J. Li and H. L. Tuller, <i>Ionic Conduction Based Polycrystalline Oxide Gamma Ray Detection - Radiation-Ionic Effects. </i>Adv. Mater., 2309253 (2024). https://doi.org/10.1002/adma.202309253