Yellow stimulated emission from Dy³⁺-doped silica glass microspheres

Dy³⁺-doped silica glass whispering gallery mode microspheres are fabricated by fiber fusion splicing. They present an almost ideal spherical morphology with a radius ranging from 60 to 67 µm, as determined by confocal laser microscopy. The host composition of the microsphere is close to that of the fiber core. The dopant Dy³⁺ ions are uniformly distributed across the microsphere, as evidenced by µ-luminescence studies, and present a luminescence lifetime of the ⁴F_9/2 state of 514.7 ± 1.1 µs, indicating a weak luminescence quenching. The Dy³⁺-doped glass microspheres were excited via evanescent field coupling using a half-tapered fiber and a blue 450-nm GaN laser diode (direct pumping scheme). The yellow fluorescence of Dy³⁺ ions (the ⁴F_9/2 → ⁶H_13/2 transition) is filtered by the whispering gallery modes (free spectral range: 0.5 nm for 67-µm radius microsphere). The onset of stimulated emission is further observed, highlighting the potential of such microresonators for narrow-linewidth light sources directly emitting visible light.