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Optimizing the spontaneous-emission of far-UVC phosphors

Far-UVC light can enable virus-deactivation while remaining harmless to human tissues. This triggered great efforts to create far-UVC light sources with sufficient emission power and efficiency. However, current sources, such as mercury lamps, KrCl excimer lamps, and LEDs, are made from hazardous chemicals or are limited by low efficiency. Consequently, an alternative approach for reaching the far-UVC is now receiving renewed interest: using phosphors for converting higher frequencies to the desired range of far-UVC. However, this concept is limited by the phosphor's conversion efficiency. In this paper, we propose to utilize principles of nanophotonics to create far-UVC sources. Specifically, we design a phosphor-dielectric multilayer that increases the efficiency of far-UVC light conversion and controls the intrinsic emission properties, including the angular spectrum and emission rate, by shaping the local density of photonic states. To exemplify our approach, we design an aperiodic multilayer nanostructure made of the phosphor material YPO4:Pr3+, showing an increase in light extraction by a factor of 3 compared to naïve bulk structures. Our approach can be applied to any phosphor material and any emitter geometry, opening avenues for engineering nanophotonic light sources in the far-UVC and other spectral regimes.