Colloidal semiconductor nanocrystals (NCs) with their highly versatile opto-electronic properties offer exciting prospects for light-emitting devices including electrically pumped light-emitting diodes and optically pumped lasers. Optical gain and lasing in these nanocrystals have been first demonstrated back in 2000, yet it has not been possible to achieve efficient optical gain until very recently. In the last years, structurally-engineered and composition-tuned nanocrystals have been developed, which could substantially suppress the undesired nonradiative loss mechanisms (e.g., Auger recombination). These innovative NC architectures have overcome the long-standing challenges inhibiting achievement of efficient optical gain in these materials and showed unprecedented optical gain performance. Here, we will highlight our recent results on the achievement of ultralow gain thresholds, record high modal gain coefficients and long gain lifetimes using interface alloyed core/shell quantum dots and heterostructured colloidal nanoplatelets [1-5]. By promoting strong excitonic properties in colloidal nanoplatelets, we realized modal gain coefficients that could exceed 1000 cm^-1 (see Fig. 1) [1, 5], better than those of the conventional semiconductor materials reported to date. These materials further enabled us to realize ultralow threshold lasing under both single- and two-photon absorption regimes with thresholds of 20 µJ/cm² [4] and 700 µJ/cm² [2], respectively. Moreover, we showed remarkably long gain lifetimes reaching 0.5 ns [5], almost an order of magnitude better than what has been commonly observed from conventional nanocrystals. Using these materials, we developed all-solution-processed and all-colloidal lasers via employing colloidal cavities (see Fig. 1) [1, 2]. These lasers show ultralow threshold gain under two-photon absorption that is highly promising for bio imaging.

Figure 1. Heterostructured colloidal nanoplatelets for record-high modal optical gain coefficients. All-colloidal nanocrystal lasers that are fabricated via solution-processing techniques.

References:

1. B. Guzelturk, Y. Kelestemur, M. Olutas, S. Delikanli, H. V. Demir, “Amplified Spontaneous Emission and Lasing in Colloidal Nanoplatelets,” ACS Nano 8, 6599 (2014).
2. B. Guzelturk, Y. Kelestemur, K. Gungor, A. Yeltik, M. Z. Akgul, W. Yue, R. Chen, H. D. Sun, C. Dang, H. V. Demir, “Stable and Low Threshold Optical Gain in CdSe/CdS Quantum Dots: All-Colloidal Frequency Up-Converted Laser" Advanced Materials 27, 2741 (2015).
3. M. Olutas, B. Guzelturk, Y. Kelestemur, A. Yeltik, S. Delikanli, H. V. Demir, “Lateral Size-Dependent Spontaneous and Stimulated Emission Properties in Colloidal CdSe Nanoplatelets” ACS Nano 9, 5041 (2015).
4. Y. Kelestemur, B. Guzelturk, O. Erdem, M. Olutas, K. Gungor, H. V. Demir, “Platelet-in-Box Colloidal Quantum Wells: CdSe/CdS@CdS Core/Crown@Shell Heteronanoplatelets” Adv. Funct. Mater. 26, 2891 (2016).
5. B. Guzelturk, Y. Kelestemur, M. Olutas, Q. Li, T. Lian, H. V. Demir, “High-Efficiency Optical Gain in Type-II Semiconductor Nanocrystals of Alloyed Colloidal Quantum Wells,” J. Phys. Chem. Lett. 8, 5317 (2017).