Low-Threshold Single-Mode Microlasers from Green CdSe/CdSeS Core/Alloyed-Crown Nanoplatelets

Colloidal nanoplatelets (NPLs), a class of semiconductor nanocrystals, have attracted considerable attention as a promising gain material for their ultralow amplified spontaneous emission (ASE) and lasing thresholds. However, there exist spectral gaps, especially in the green-color range, that NPLs cannot fully cover. The recently developed CdSe/CdSeS core/alloyed-crown NPLs with excellent tunability across the green-color range offer the possibility to remedy this deficiency. Here, the ASE and lasing characteristics of this new type of NPL are investigated. A remarkably low ASE threshold of 16 μJ/cm2 at 522 nm is measured, the lowest among core/crown NPLs. Microlasers are fabricated by spin-coating them on second-order distributed feedback (DFB) cavities developed in silicon nitride (SiN) substrates. The microlasers exhibit an ultralow lasing threshold of 9 μJ/cm2 at 522 nm. Moreover, they can cover a spectral range of 505–535 nm with all clean single-mode emissions. Picosecond time- and spectral-resolved photoluminescence (PL) spectroscopy reveals that the gain band is determined by the biexciton emission bandwidth. The vigorous development of NPLs with low lasing thresholds in a broad spectral range will greatly facilitate the realization of nanocrystal-based lasers.