Enhanced biocidal activity of Pr³⁺ doped yttrium silicates by Tm³⁺ and Yb³⁺ co-doping

We present an enhancement of optically triggered anti-microbial treatment based on visible to ultraviolet up-conversion emission in lanthanide-doped yttrium silicates. A series of Pr³⁺/Tm³⁺/Yb³⁺ co-doped Y₂Si₂O₇ powders was synthesized and characterized, including determination of their crystal structure, morphology, and spectroscopic properties. The emphasis was put on the examination of the influence of lanthanide ion doping on the luminescence characteristics in the ultraviolet region of light, since the emission from this part of the spectra can be effectively used for decontamination purposes. Due to the additional Tm³⁺ doping into the Pr³⁺ containing Y₂Si₂O₇ powders, we observed up-conversion emission lines in both UVA and UVC regions of spectra, while the solely Pr³⁺ doped materials gave only the emission in the UVC region. The synthesized luminescent powders were further used for decontamination experiments with three different types of pathogenic microorganisms (i.e., A. baumannii, S. aureus, and C. albicans) formed biofilms. The microbial cell viability studies demonstrated the higher deactivation efficiency for all investigated microbial species with the use of combined UVA and UVC irradiation generated by Pr³⁺ and Tm³⁺ co-doped phosphors. At the same time, the incorporation of Yb³⁺ ions could additionally offer an alternative NIR-to-UVA excitation pathway via a 980 nm laser diode, which is beneficial for deeper light penetration experiments.