Discovering the Potential of High Phonon Energy Hosts in the Field of Visible-to-Ultraviolet C Upconversion

The recent pandemic has intensified the search for new ultraviolet C (UVC) phosphors excited by low-intensity visible light that can be used for disinfection or therapeutic purposes. Currently, the most promising phosphor with efficient upconversion was thus far Y₂SiO₅ (YSO) doped with Pr³⁺. However, we have studied a new material Sr₃(BO₃)₂:Pr³⁺ (SBO), whose upconversion emission is 10 times stronger than YSO, despite the high phonon energy possessed by SBO and despite the lack of optimization of synthesis and dopant concentration and the absence of co-dopant that should be added to compensate for the charge. Such an efficient upconversion is achieved by engagement of the ¹D₂ level, which is populated by both the multiphonon non-radiative transition and the closed feedback loop. From this level, blue excitation can reach the 4f¹5d¹ electronic configuration. At the same time, due to a small Stokes shift, the 5d levels emit exclusively in the UVC and partially in the ultraviolet B (UVB) region.