Robust low threshold full-color upconversion lasing in rare-earth activated nanocrystal-in-glass microcavity

Visible light microlasers are essential building blocks for wide-ranging applications from integrated photonics to quantum computing. However, achieving low-threshold (µW), continuous-wave (CW) visible light lasing at room temperature (RT) has been a challenge because of the formidable requirement of population inversion at short wavelengths. Rare-earth (RE)-activated microcavities, featuring the merits of high-quality factor ( Q ) and small mode volume of whispering gallery modes, offer the great opportunity for achieving infrared-to-visible upconversion (UC) lasing. Here, nano-glass composite (GC) microspheres are fabricated incorporating RE-doped fluoride nanocrystals with highly efficient UC emissions. These multi-phase composite microspheres exhibit a high Q value (≥ 10 ⁵ ), comparable to that of conventional multi-component glass microspheres. The UC lasing at pure red, green and blue (RGB) are demonstrated from a tapered fiber-microsphere system, and the RGB color gamut covered by the lasing is 106.26% of the standard of national television system committee. The superiority of the GC microspheres is clearly manifested by the reduced (by 45%) lasing threshold and enhanced (more than four times) slope efficiency. This, together with the excellent long-term stability suggests a promising solution to achieving highly robust, low-threshold and versatile UC microlasers.