Solid-liquid phase transition of CuCl nanocrystals embedded in glass: A versatile sustainable platform for high-contrast analog optical switching

We demonstrate a novel approach to show high-contrast thermo-optical switching by profiting from the solid–liquid phase transition of CuCl nanocrystals embedded in a transparent borosilicate glass. These nanostructured glasses exhibit a distinct excitonic absorption in the near-UV region (369 nm), which undergoes significant modulation upon thermally induced phase changes of the CuCl nanocrystals. Exploiting the low melting point of CuCl relative to the glass matrix, we achieve thermally reversible solid–liquid–solid transitions, producing a pronounced optical hysteresis effect. Notably, by heating beyond the melting point, an approach that has not previously explored, we observe a larger optical hysteresis contrast than reported in earlier studies, and with a distinct sail-like shape. Furthermore, we show that these transitions can be selectively interrupted at different heating (cooling stages), enabling multilevel analog optical switching. These findings highlight the exceptional potential of CuCl-doped glasses as a robust, sustainable and tunable platform for advanced optoelectronic applications, paving the way for innovative optical memory and signal processing technologies.