Electrically Excited Multi-Color Amplified Spontaneous Emission from Colloidal Quantum Dots

Solution-processable materials, including organic semiconductors, perovskites, and colloidal quantum dots (QD), have been under intense investigation as optical-gain media for future laser technologies. However, the realization of electrically driven laser action with these materials still remains an unrealized objective. Colloidal continuously-graded QDs (cg-QDs) have recently emerged as a promising system for achieving lasing with electrical excitation. Thanks to strong suppression of Auger recombination, they showed optical gain under electrical pumping and allowed for demonstrating dual-function devices that operated as an optically pumped laser and a high-brightness light-emitting diode (LED).^1-3 Notably, cg-QDs exhibit good stability at current densities of over 1 kA cm^-2, which allowed for realizing unusual two-band electroluminescent (EL) wherein the higher-energy 1P feature was more intense than the band-edge 1S emission.² This is indicative of very high per-dot excitonic occupancies that were sufficient to generate strong, broad-band optical gain spanning the 1S and 1P transitions. However, light amplification due to stimulated emission from the QDs was not observed because of strong optical losses in charge-conducting layers of the EL device.³ Here, we tackle this problem but integrating QDs with a specially engineered photonic waveguide. Using this approach, we maximize the mode confinement factor for the gain-active QD layer and reduce the field intensity in the optically lossy charge conducting layers. As a result, the developed devices generate large net optical gain under pulsed bias and demonstrate ASE-type laser action at three optical transitions (abbreviation ‘ASE’ stands for ‘amplified spontaneous emission’).⁴ The realization of the ASE regime is indicated by multiple observables including a super-linear growth of the EL intensity above the ASE threshold, a pronounced line narrowing, the emergence of preferred polarization, high directionality of edge-emitted light, and an exceptionally high output intensity which reaches ~2 kW cm^-2.<br/>1. H. Jung, <u>N. Ahn</u>, V. I. Klimov, <i>Nature Photonics</i>, <b>15</b>, 643-655 (2021)<br/>2. H. Jung, Y.-S. Park, <u>N. Ahn</u>, J. Lim, I. Fedin, C. Livache, V. I. Klimov, <i>Nature Communications</i>, <b>13</b>, 3734 (2022)<br/>3. <u>N. Ahn</u>, Y.-S. Park, C. Livache, J. Du, K. Gungor, J. Kim, V. I. Klimov, arXiv preprint arXiv:2204.01929 (2022)<br/>4. <u>N. Ahn</u>, C. Livache, V. Pinchetti, H. Jung, H. Jin, Y.-S. Park, V. I. Klimov, under review, (2022)