Broadband Amplified Spontaneous Emission and Random Lasing from Wurtzite CdSe/CdS "Giant-Shell" Nanocrystals

Colloidal nanocrystals (NCs) are attractive materials for light-emitting applications thanks to their flexible synthesis, size-dependent properties, and bright emission. Yet, colloidal NCs still present a narrow gain band (full-width half maximum around 10 nm), which limits their application to single-color lasers. Widening of the gain band by specifically engineered NCs can further improve the prospect of this class of materials toward the fabrication of solution-processed white-emitting or color-tunable lasers. Here, we report broadband amplified spontaneous emission (ASE) from wurtzite CdSe/CdS "giant-shell" nanocrystals (g-NCs) with an unprecedented large core up to 7.5 nm in diameter that were synthesized through a continuous injection route. The combination of large core and shell enables ASE from different CdSe optical transitions as well as from the CdS. Importantly, thin films of g-NCs with a large CdSe core (7.5 and 5.1 nm in diameter) show ASE at different colors with a similar threshold, indicating that light emission amplification can be achieved from different optical transitions simultaneously. Tuning of the core diameter allows obtaining ASE in a wide spectral range, and blending of g-NCs with different core sizes gives rise to a continuous amplified spontaneous emission band from green to red (510 to 650 nm). Drop-cast films of CdSe/CdS g-NCs demonstrate simultaneous dual-color random lasing under nanosecond-pulsed excitation.