Ultrahigh Green and Red Optical Gain Cross-sections from Solutions of Colloidal Quantum Well Heterostructures

Optical gain in solution, which provides high photostability as a result of continuous regeneration of the gain medium, is extremely attractive for optoelectronic applications. Here, we propose and demonstrate amplified spontaneous emission (ASE) in solution with ultralow thresholds of 30 mikroJ/cm2 in red and of 44 mikroJ/cm2 in green from engineered colloidal quantum well (CQW) heterostructures. For this purpose, CdSe/CdS core/crown CQWs, designed to hit the green region, and CdSe/CdS/CdxZn1-xS core/crown/gradient-alloyed shell CQWs, further tuned to reach the red region by shell alloying, were employed to achieve high-performance ASE in the visible. The net modal gain of these CQWs reaches 530 cm-1 for the green and 201 cm-1 for the red, two orders of magnitude larger than those of colloidal quantum dots (QDs) in solution owing to intrinsically larger gain cross-sections of these CQWs. To explain the root cause for ultrahigh gain coefficient in solution, we show that for the first time that the gain cross-sections of these CQWs is 3.3x10-14 cm2 in the green and 1.3x10-14 cm2 in the red which are two orders magnitude larger compared to those of CQDs. These findings confirm the extraordinary prospects of these solution-processed CQWs as solution-based optical gain media in lasing applications.