From Visible Light to UVC: Upconverting Phosphor Doped with Pr³⁺ Ions for Germicidal Applications

Antibiotic resistance is a global health crisis driven by the overuse and misuse of antibiotics. To combat this, effective disinfection of air, water, and surfaces is crucial. Ultraviolet C (UVC) lamps, emitting 220-280 nm radiation, have been used for this purpose since the 1930s. Since UVC radiation does not naturally reach the Earth's surface, microbes have not developed resistance to it.

In this work, we synthesized UVC-emitting phosphor doped with Pr³⁺ ions via a high-temperature solid-state reaction. Praseodymium ions are highly effective for UV luminescence due to their interconfigurational transitions between the 5d and 4f levels. Upon Stokes excitation, we observed broad-band emission in the 230–350 nm range, corresponding to the 4f5d → ³H_j and ³F_j transitions. Notably, the same results were obtained with visible (444 nm) excitation. This upconversion (UC) of visible light into UVC can occur through two mechanisms: energy transfer upconversion (ETU) and excited-state absorption (ESA). We analyzed UC luminescence's dependence on the pumping power and Pr³⁺ concentration, as well as the decay kinetics of upconverted light, and found that both mechanisms can occur with varying effectiveness.

The upconversion properties of the prepared materials make them attractive candidates for mercury-free UVC devices, where high-energy photons can be generated by excitation with low-energy radiation. Additionally, these materials have the potential for use in self-cleaning surfaces that emit UVC radiation when exposed to sunlight [2].

This work was supported by The National Science Centre (NCN) under the OPUS 21 project, grant no. UMO-2021/41/B/ST5/03792, which is gratefully acknowledged.

References

[1] Reed, N.G. The History of Ultraviolet Germicidal Irradiation for Air Disinfection. Public Health Reports 2010, 125, 15–27.

[3] Cates, E.L.; Cho, M.; Kim, J.-H. Converting Visible Light into UVC: Microbial Inactivation by Pr ³⁺ -Activated Upconversion Materials. Environ Sci Technol 2011, 45, 3680–3686.