Scientists at Los Alamos National Laboratory have incorporated meticulously engineered colloidal quantum dots into a new type of LED containing an integrated optical resonator, which allows the LEDs to function as lasers. The researchers demonstrated an operational LED that also functioned as an optically pumped, low-threshold laser. To achieve those goals, they incorporated an optical resonator directly into the LED architecture without obstructing the charge-carrier flows into the quantum dot emitting layer. By carefully designing the structure of their multilayered device, the researchers achieved confinement of the emitted light within the ultrathin quantum dot medium on the order of 50 nm across. These are colloidal quantum dots operating in LED mode. Courtesy of Los Alamos National Laboratory. This is key to obtaining the lasing effect and, at the same time, allowing for efficient excitation of the quantum dots by the electrical current. The final ingredient of this successful demonstration was unique, homemade quantum dots perfected for lasing applications per recipes developed by the Los Alamos team over the years of research into the chemistry and physics of these nanostructures. According to researchers, these dual-function devices clear the path toward versatile, manufacturing-friendly laser diodes. The technology can potentially revolutionize numerous fields from photonics and optoelectronics to chemical sensing and medical diagnostics. “This latest breakthrough along with other recent advances in quantum dot chemistry and device engineering that we have achieved suggest that laser diodes assembled from solution may soon become a reality,” said Victor Klimov, head of the quantum dot group at Los Alamos National Laboratory. “Quantum dot displays and television sets are already available as commercial products. The colloidal quantum dot lasers seem to be next in line.” The devices can be made using cheaper and simpler methods of manufacturing compared to modern semiconductor laser diodes which require sophisticated, vacuum-based, layer-by-layer deposition techniques. Solution-processable lasers can be produced in less challenging lab and factory conditions, and could lead to devices that would benefit a number of emerging fields, including integrated photonic circuits, optical circuitry, lab-on-a-chip platforms, and wearable devices. For the past two decades, the Los Alamos quantum dot team has been working on fundamental and applied aspects of lasing devices based on semiconductor nanocrystals prepared via colloidal chemistry. These particles, also known as colloidal quantum dots, can be easily processed from their native solution environment to create various optical, electronic, and optoelectronic devices. Furthermore, they can be “size-tuned” for lasing applications to produce colors not accessible with existing semiconductor laser diodes. Currently, the Los Alamos scientists are tackling the remaining challenge, which is boosting the current density to levels sufficient for obtaining so-called population inversion — the regime when the quantum dot active medium turns into a light amplifier. The research was published in Nature Communications (www.doi.org/10.1038/s41467-019-14014-3).