Long-lived near-infrared photoinduced absorption in LaSrAlO4 excited with visible light

Here, we report on studies of photoinduced carrier dynamics in LaSrAlO4. In samples annealed in a reductive atmosphere, intense illumination by sub-band-gap photons results in strong photoinduced absorption (PIA) centered at about 0.7 eV. As a function of temperature, PIA disappears above 200 K, but at 4 K, it has a lifetime of several hours. The nonlinear dependence of PIA on light fluence enables writing or erasing this optical memory effect by using visible and infrared photons, respectively. Our results can be explained within a three-level scheme and are discussed in a scenario that involves trapping of photoexcited electrons at oxygen-vacancy sites.