We propose and demonstrate construction of highly uniform, multilayered superstructures of CdSe/CdZnS core/shell colloidal nanoplatelets (NPLs) using liquid interface self-assembly. These NPLs are sequentially deposited onto a solid substrate into slabs having monolayer-precise thickness across tens of cm 2 areas. Because of near-unity surface coverage and excellent uniformity, amplified spontaneous emission (ASE) is observed from an uncharacteristically thin film having 6 NPL layers, corresponding to a mere 42 nm thickness. Furthermore, systematic studies on optical gain of these NPL superstructures having thicknesses ranging from 6 to 15 layers revealed the gradual reduction in gain threshold with increasing number of layers, along with a continuous spectral shift of the ASE peak (∼18 nm). These observations can be explained by the change in the optical mode confinement factor with the NPL waveguide thickness and propagation wavelength. This bottom-up construction technique for thickness-tunable, three-dimensional NPL superstructures can be used for large-area device fabrication.

Whispering gallery mode (WGM) resonators are shown to hold great promise to achieve high-performance lasing using colloidal semiconductor nanocrystals (NCs) in solution phase. However, the low packing density of such colloidal gain media in the solution phase results in increased lasing thresholds and poor lasing stability in these WGM lasers. To address these issues, here optical gain in colloidal quantum wells (CQWs) is proposed and shown in the form of high-density close-packed solid films constructed around a coreless fiber incorporating the resulting whispering gallery modes to induce gain and waveguiding modes of the fiber to funnel and collect light. In this work, a practical method is presented to produce the first CQW-WGM laser using an optical fiber as the WGM cavity platform operating at low thresholds of ≈188 µJ cm −2 and ≈1.39 mJ cm −2 under one-and two-photon absorption pumped, respectively, accompanied with a record low waveguide loss coefficient of ≈7 cm −1 and a high net modal gain coefficient of ≈485 cm −1 . The spectral characteristics of the proposed CQW-WGM resonator are supported with a numerical model of full electromagnetic solution. This unique CQW-WGM cavity architecture offers new opportunities to achieve simple high-performance optical resonators for colloidal lasers.

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Lasers based on semiconductor colloidal quantum wells (CQWs) have attracted wide attention thanks to the facile solution-processability, low threshold and wide range spectral tunability. Colloidal microlasers based on whispering-gallery-mode (WGM)...