Green stimulated emission boosted by nonradiative resonant energy transfer from blue quantum dots

Abstract

Thanks to their tunability and versatility, colloidal quantum dots (CQDs) have been attracting very much interest for laser technology. Such CQDs made of II-VI semiconductor compound offer the potential to bridge the “green gap” in conventional semiconductor materials. However, in optical pump laser configuration, when the energy of excitation photons is much greater than that of emission photons, multiexciton interaction is enhanced, leading to reduced stimulated emission cross-section, broadened gain bandwidth, and enhanced photoinduced absorption. Here, to circumvent this drawback, for the first time, we show a fully colloidal gain in green enabled by a partially indirect pumping approach assisted by Förster resonance energy transfer process from blue-emitting CQDs to green ones. By introducing the blue CQDs as exciton donors, the lasing threshold of the acceptor, green CQDs, is reduced dramatically although the photon energy of optical pump is much higher compared to the bandgap energy. The blue CQDs thus serve as an energy-transferring buffer medium to reduce excitation energy from pumping photons in a controlled way by injecting photo-induced excitons into green CQDs. Our newly developed colloidal pumping scheme could enable efficient CQD lasers of full visible colours by a single pump source and cascaded exciton transfer. This would potentially pave the way for an efficient multicolour laser for lighting and display applications.