Lasing is observed from carbon nanodots (C-dots) dispersed into a layer of poly(ethylene glycol) coated on the surface of optical fibers under 266 nm optical excitation. This is due to the enhancement of photoluminescence intensity via the esterification of carboxylic groups of the C-dots, and the formation of high-Q cylindrical microcavities to support second-type whispering gallery modes.

Experimental processPreparation of water-soluble GQDs: The water-soluble GQDs were prepared by microwave-assisted hydrothermal pyrolysis method. The glucose (Sigma-Aldrich, > 99.5%) was dissolved in deionized water with the concentration of ~11 wt%. The solutions were tapped to the glass bottle with tightened cover. The glass bottle was heated with a conventional microwave oven (Galanz P70B17L-T1) at a power of 595 W for a specific time (1, 3, 5, 7 and 9 min). Followed by the microwave irradiation, the GQD solutions were cooled down to room temperature under air ambient without further purification.Preparation of GQD/agar composite: 10 mg of agar flakes (Chancevon Agar) was inserted into 2 mL of the GQD solution at 85°C under vortex mixing. The mixture was well stirred and heated until it became homogeneous with the solution.Subsequently the mixture was poured into a 0.8 cm diameter glass tube mound and was cooled down to room temperature under ambient atmosphere.

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