Nanocrystal lasing in the single-exciton regime using engineered exciton-exciton interactions

Because of size-controlled emission color, good photostability, and chemical flexibility, colloidal semiconductor nanocrystals (NCs) are promising building blocks for new types of colorselectable optical gain media [1]. One factor limiting optical gain performance ofNCs is highly efficient multiexciton Auger recombination that leads to short picosecond optical gain life times [2]. Recent attempts to suppress Auger recombination utilized NC shape control [3, 4]. Using elongated CdSe NCs (quantum rods) it was possible to extend optical gain life times by almost an order of magnitude, which further allowed a many-fold reduction of the excitation threshold for amplified spontaneous emission (ASE) [4]. For both spherical and elongated particles, Auger recombination times rapidly shorten as the particle dimensions are decreased. Therefore, it becomes progressively more difficult to achieve the ASE regime for shorter wavelengths that require the use of NCs of small sizes. In particular, while demonstrating strong optical-gain performance in the red-yellow spectral ranges, CdSe NCs do not show efficient ASE in the range of green and particularly blue colors that correspond to extremely small NC sizes (< 3nm).