No abstract

Colloidal quantum dots exhibit efficient photoluminescence with widely tunable bandgaps as a result of quantum confinement effects. Such quantum dots are emerging as an appealing complement to epitaxial semiconductor laser materials, which are ubiquitous and technologically mature, but unable to cover the full visible spectrum (red, green and blue; RGB). However, the requirement for high colloidal-quantum-dot packing density, and losses due to non-radiative multiexcitonic Auger recombination, have hindered the development of lasers based on colloidal quantum dots. Here, we engineer CdSe/ZnCdS core/shell colloidal quantum dots with aromatic ligands, which form densely packed films exhibiting optical gain across the visible spectrum with less than one exciton per colloidal quantum dot on average. This single-exciton gain allows the films to reach the threshold of amplified spontaneous emission at very low optical pump energy densities of 90 µJ cm(-2), more than one order of magnitude better than previously reported values. We leverage the low-threshold gain of these nanocomposite films to produce the first colloidal-quantum-dot vertical-cavity surface-emitting lasers (CQD-VCSEL). Our results represent a significant step towards full-colour single-material lasers.

the precursors flowed into the heated section, where they quickly reacted to form NCs. The NC solution was then collected for absorption and photoluminescence measurements.Optical absorption spectra were acquired using a Hewlett-Packard 8453 diode array spectrometer. Photoluminescence spectra were acquired using a SPEX Fluorolog 1680 spectrometer, using right-angle collection. Samples were prepared by diluting the raw NC solutions in hexane. Quantum yields were determined by comparing the integrated emission of a given NC sample solution with that of an appropriate reference dye [18].

We demonstrate a solvent-free contact printing process for deposition of patterned and unpatterned colloidal quantum dot (QD) thin films as the electroluminescent layers within hybrid organic-QD light-emitting devices (QD-LEDs). Our method benefits from the simplicity, low cost, and high throughput of solution-processing methods, while eliminating exposure of device structures to solvents. Because the charge transport layers in hybrid organic/inorganic QD-LEDs consist of solvent-sensitive organic thin films, the ability to avoid solvent exposure during device growth, as presented in this study, provides a new flexibility in choosing organic materials for improved device performance. In addition, our method allows us to fabricate both monochrome and red-green-blue patterned electroluminescent structures with 25 microm critical dimension, corresponding to 1000 ppi (pixels-per-inch) print resolution.

The ability to synthesize semiconductor nanocrystals with narrow size distributions and high luminescent efficiencies has made quantum dots an attractive alternative to organic molecules in applications such as optoelectronic devices [1,2] and biological fluorescence labeling. [3][4][5] Not only are quantum dots (QDs) more stable to photooxidation relative to organic molecules, but their fluorescence is also more saturated (narrow emission bandwidths). Their size-tunable optical properties, which are independent of their chemical