Abstract
<title>Abstract</title> <p>We report an optical setup designed to monitor the radiance emitted by a millimeter-sized sodium carboxymethyl cellulose (CMC) aerogel loaded with Y2O3:Eu3+ microphosphors under tritium exposure. The device was first studied during tritium filling and then monitored after sealing over 16 months. The radiance showed an atypical non-monotonic evolution, with an initial decrease after sealing, followed by a sustained increase over 7 months, a stabilization period, and a recent decline. To the best of our knowledge, this is the first systematic long-term monitoring of a tritium-powered solid-state radioluminescent light source (SRLS) reported in the literature. These results suggest that multiple mechanisms may act sequentially or in parallel during long-term exposure, involving both the aerogel matrix and the luminescent microphosphors. Further radiochemical and materials characterization under radioactive atmosphere will be required to clarify the role of tritium in the observed radiance evolution. This work also highlights the potential of radioluminescent devices as long-term light sources for implantable photobiomodulation applications.</p>