Lanthanide-doped nanocrystals in high-Q microtoroids for stable on-chip white-light lasers

The plentiful energy states of lanthanide (Ln(3+))-doped nanomaterials make them very promising for on-chip integrated white-light lasers. Despite the rapid progresses, the Ln(3+)-based white upconversion emissions are strongly restricted by their low upconversion quantum efficiency and the color stability. Herein, we combine the CaF2:Yb35Tm1.5Er0.5 nanocrystals and the high-Q microtoroids, and experimentally demonstrate the chip-integrated stable white-light laser. By optimizing the sizes, density, and distributions of LnLn(3+)-doped nanocrystals, the Q factors of Ln(3+)-doped microtoroids are maintained as high as 5 x 10(5). The strong light matter interaction in high-Q microtoroids greatly enhances the upconversion emission and dramatically reduces the laser thresholds at 652 nm, 545 nm, and 475 nm to similarly low values (1.89-2.10 mJ cm(-2)). Consequently, robust white-light microlaser has been experimentally achieved from a single microtoroid. This research has paved a solid step toward the chip-scale integrated broadband microlasers. (C) 2022 Chinese Laser Press