Ultraviolet upconversion in thulium-doped fluorozirconate fiber observed under two-color excitation

Ultraviolet upconversion signals at 293, 351, and 366 nm were observed from thulium-doped fluorozirconate fiber pumped with a 458-nm Ar(+) laser. The upconversion signal's intensity was enhanced 5x when the fiber was simultaneously pumped with a 458-nm Ar(+) laser and a 585-nm dye laser. There is evidence of the formation of defect centers under simultaneous excitation by visible and near-infrared lasers (458 and 750 nm), and there is no evidence of color-center formation when both of the exciting beams are in the visible (458 and 585 nm).