We report the observation of amplified spontaneous emission in silica‐based single‐mode optical fibers doped with Tm3+. Frequency upconverted emission was observed in a number of visible and near‐infrared lines after pumping by 1064 nm radiation. The upconversion process is induced via the nonlinear absorption of the infrared beam and enhanced by stimulated Raman scattering in the fiber, leading to amplified spontaneous emission in the blue (∼473 nm) region.