Selenium-doped zeolites as sustainable NIR emitters: a comprehensive photophysical study

Abstract

In this study, the photophysical properties of selenium-doped aluminosilicate zeolites were thoroughly investigated, revealing distinct optical properties according to the selenium loading. At lower selenium concentrations, a paramagnetic [Se₂]⁻ species was identified, exhibiting an emission at 755 nm with an external quantum efficiency (EQE) of 51% and a photoluminescent decay time of 98 nanoseconds. As selenium content increases, a new near-infrared (NIR) emitting species emerges, featuring a substantial Stokes shift (1.6 eV), a 55 μs lifetime, and an EQE of 14%. Combined with their high stability and sustainable composition, these properties make selenium-doped zeolites competitive candidates among current NIR emitters. This marks a considerable change in the material's optical properties. This phenomenon is further accompanied by a decrease in the intensity of the electron paramagnetic resonance (EPR) spectra. Using time-resolved optical spectroscopy, EPR, and X-ray diffraction, we investigated the mechanism behind this transformation. The results clarify the processes leading to the formation of phosphorescent NIR-emitting chalcogen clusters within zeolite frameworks. Leveraging their unique NIR properties, these materials were successfully tested in a proof-of-concept as effective anticounterfeiting and security tags. This work addresses existing gaps in the literature on luminescent chalcogen-doped materials and highlights their potential in emerging NIR technologies.