Two-band optical gain and ultrabright electroluminescence from colloidal quantum dots at 1000 A cm-2

Colloidal quantum dots (QDs) are attractive materials for the realization of solutionprocessable laser diodes. Primary challenges towards this objective are fast optical-gain relaxation due to nonradiative Auger recombination and poor stability of colloidal QD solids under high current densities required to obtain optical gain. Here we resolve these challenges and achieve broad-band optical gain spanning the band-edge (1S) and the higher-energy (1P) transitions. This demonstration is enabled by continuously graded QDs with strongly suppressed Auger recombination and a current-focusing device design, combined with short-pulse pumping. Using this approach, we achieve ultra-high current densities (similar to 1000 A cm(-2)) and brightness (similar to 10 million cd m(-2)), and demonstrate an unusual two-band electroluminescence regime for which the 1P band is more intense than the 1S feature. This implies the realization of extremely large QD occupancies of up to similar to 8 excitons per-dot, which corresponds to complete filling of the 1S and 1P electron shells.

Automated summary

This study addresses the challenges of fast optical-gain relaxation and poor stability in colloidal quantum dot (QD) solids, and achieves broad-band optical gain. By using continuously graded QDs and a current-focusing device design, combined with short-pulse pumping, ultra-high current densities and brightness are achieved, demonstrating an unusual two-band electroluminescence regime.