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Temporal and spatial tuning of the refractive index of optical thin films is desired for flat optics applications. The redistribution of mobile ions in mixed ionic-electronic conductors (MIEC) has been demonstrated to serve as a viable means for achieving optical tuning down to the nanoscale. Here we studied the dynamic range of the optical tuning achievable in the refractive index, in the MIEC oxide – PrxCe1−xO2−δ (PCO), for x = 0.1, 0.2 and 0.4, at 500 °C, by in-situ spectrophotometry. Significant increases in the modulation of both the imaginary and real optical constants in the visible and the adjacent spectra were obtained for increased doping levels. Device employing an electrochemical titration method was implemented to modulate the oxygen concentration, and thereby the optical transmission of PCO. Incorporation of a patterned top electrode allowed for the demonstration of spatial control of PCO thin film properties by in-situ video imaging of the optical switching process. The electrochemically induced optical state is shown to remain non-volatile upon quenching the device to room temperature under applied bias. [ABSTRACT FROM AUTHOR]

Mixed ionic–electronic conductors offer chemical and electrical means for active tuning of their optical constants, e.g., with variations in oxygen non‐stoichiometry in Pr0.1Ce0.9O2–δ, enabling implementation of adaptive thin film optical devices. In situ chemo‐tuning of the extinction coefficient in Pr0.1Ce0.9O2–δ at elevated temperatures is demonstrated and a tuning model is provided that treats the interdependence of mobile oxygen vacancies and small polarons coupled to variations in optically active praseodymium ions. Furthermore, a new means for electro‐tuning of the optical constants of mixed ionic–electronic conductors is demonstrated experimentally and modeled for Pr0.1Ce0.9O2–δ thin films deposited on grid‐like electrode structures. Modeling of non‐steady‐state optical transmittance modulations in the latter allows for estimation of oxygen vacancy mobility that determines the switching speed of the device. Quenched‐in values of nr and k to room temperature become nonvolatile, providing a modulation range in the extinction coefficient of Δk ≈ 0.1 (change of ≈800%) and in the refractive index of Δnr ≈ 0.1 (relative to initial nr of ≈2.35). Key figures of merit, including transmission optical modulation of ≈0.04 per 1 mV nm–1, switching energy per area of 1.9 nJ µm–2, and switching times of seconds, are demonstrated, with further improvements possible. [ABSTRACT FROM AUTHOR]