Optical gain and lasing in colloidal quantum dots

Summary form only given. Semiconductor quantum dots (QDs) promise the lowest lasing threshold for semiconductor media. Additionally, QDs in the strong confinement regime have an emission wavelength that is a pronounced function of size, adding the advantage of continuous spectral tunability simply by changing the dot radius. Lasing has previously been demonstrated for epitaxially grown III-V QDs. Large lateral dimensions and difficulties in size control limit their spectral tunability using quantum confinement effects. An alternative approach to fabricating QDs is through chemical synthesis which can produce semiconductor nanoparticles (colloidal QDs) with radii from 1 to 6 nm and with size dispersions as small as 5%. Such dots show strong quantum confinement and permit size-controlled spectral tunability over an energy range as wide as 1 eV. The combination of tunable electronic energies and chemical flexibility make colloidal QDs ideal building blocks for the bottom-up assembly of optical device structures, including optical amplifiers and lasers. However, despite more than a decade of effort, lasing in small-size colloidal nanoparticles has not been realized. To determine what hinders lasing action, we performed extensive dynamical studies of radiative and nonradiative processes in CdSe colloidal QDs.