Figure 2. Optical gain in organic-ligand- and inorganic-halide-capped CQDs.

Film absorption and edge emission spectra below and above ASE threshold for organic-ligand- (a) and inorganic-halide-capped (b) CQD films. The film thickness (300 nm for organic, 120 nm for inorganic) corresponds to approximately equal optical density at a pump wavelength of λ=355 nm. (c) Emission as a function of average pump peak power density or energy density. The ASE threshold is 83 kW cm⁻² for organic-ligand-capped and 51 kW cm⁻² for inorganic-halide-capped CQDs. (d) Modal gain measured by variable stripe length measurement for the organic-ligand- (750 cm⁻¹) and inorganic-halide (1,200 cm⁻¹)-capped CQD films excited at an average pump power density ^∼4 × ASE threshold for each film.