Upconversion under polychromatic excitation: Y2SiO5:Pr3+, Li+ converts violet, cyan, green, and yellow light into UVC

• An upconversion phosphor was studied using polychromatic excitation.
• Numerous excitation wavelengths contributed to excited state absorption.
• Enhancement effect was found to be dependent on relative excitation intensities.

Due to their unique ability to amplify photon energies, upconversion (UC) materials are being studied for numerous potential applications to light-utilizing technologies. Many such uses of UC demand adequate conversion efficiency under low-power, broad spectrum irradiation; however, spectroscopic studies of UC phosphors have been most commonly conducted using monochromatic laser excitation that is resonant with the desired electronic transitions. In this study, we sought to elucidate the behavior of UC materials under polychromatic excitation by initiating visible-to-UV UC in a Pr3+-doped phosphor under multiple combined two-color excitation beams. Several wavelengths of light, which were not capable of producing UC emission when used alone, were found to contribute to UC when combined with other colors, indicating that polychromatic UC mechanisms warrant consideration in applications involving broad band excitation.

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