These successes explain the continuing appeal of this field to a broad community of scientists and engineers, which in turn ensures even more exciting results to come from future exploration of this fascinating class of materials. We examine the considerable recent progress on these multiple fronts of nanocrystal research, which has resulted in the first commercialized QD technologies. Examples of such advanced control of nanocrystal functionalities include the following: interface engineering for suppressing Auger recombination in the context of QD LEDs and lasers Stokes-shift engineering for applications in large-area luminescent solar concentrators and control of intraband relaxation for enhanced carrier multiplication in advanced QD photovoltaics. A specific underlying theme is innovative concepts for tuning the properties of QDs beyond what is possible via traditional size manipulation, particularly through heterostructuring. The focus of this review is on recent advances in nanocrystal research related to applications of QD materials in lasing, light-emitting diodes (LEDs), and solar energy conversion. The field of nanocrystal quantum dots (QDs) is already more than 30 years old, and yet continuing interest in these structures is driven by both the fascinating physics emerging from strong quantum confinement of electronic excitations, as well as a large number of prospective applications that could benefit from the tunable properties and amenability toward solution-based processing of these materials. The ASE in the blue range has never been previously achieved using traditional NCs with type I carrier localization. We use these novel hetero-NCs to demonstrate efficient amplified spontaneous emission (ASE) that is tunable across a “difficult” range of green and blue colors. This effect leads to reduced optical-gain thresholds and can potentially allow lasing in the single-exciton regime, for which Auger recombination is inactive. We show that such hetero-NCs can exhibit strong repulsive exciton−exciton interactions that lead to significantly reduced excited-state absorption associated with NCs containing single electron−hole pairs. Here we explore a novel approach to achieve NC lasing in the Auger-recombination-free regime by using type II NC heterostructures that promote spatial separation of electrons and holes. The technological potential of NCs as lasing materials is, however, significantly diminished by highly efficient nonradiative Auger recombination of multiexcitons leading to ultrafast decay of optical gain. B 47, 1359–1365 (1993).Size-controlled spectral tunability and chemical flexibility make semiconductor nanocrystals (NCs) attractive as nanoscale building blocks for color-selectable optical-gain media. Komiyama, ”Quantum confinement in semiconductor heterostructure nanometer-size particles,” Phys. Alivisatos, ”Epitaxial growth of highly luminescent CdSe/CdS core/shell nanocrystals with photostability and electronic accessibility,” J. Henderson, et al., ”The optical properties of wide bandgap binary II-VI superlattices,” J. O’Donnell, ”Band alignments in Zn(Cd)S(Se) strained layer superlattices,” Semicond. Nethercot, ”Prediction of Fermi energies and photoelectric thresholds based on electronegativity concepts,” Phys. Duke, ”Space-charge effects on electron tunneling,” Phys. Feldmanna, ”Energy transfer with semiconductor nanocrystals,” J. Polli, et al., ”Ultrafast electron-hole dynamics in core/shell CdSe/CdS dot/rod nanocrystals,” Nano Lett. Toprak, et al., ”Photoluminescence from quasi-type-II spherical CdSe-CdS core-shell quantum dots,” Appl. Marcinkevicius, et al., ”Synthesis of tetrahedral quasi-type-II CdSe-CdS coreshell quantum dots,” Nanotechnology 22, 425202 (2011). Willatzen, ”Bandstructures of conical quantum dots with wetting layers,” Nanotechnology 15, 1–8 (2004).Ī. Wang, ”Electronic structures of the CdSe/CdS coreshell nanorods,” ACS Nano 4, 91–98 (2010). Bawendi, ”Optical gain and stimulated emission in nanocrystal quantum dots,” Science 290, 314–317 (2000). Piryatinski, ”Single-exciton optical gain in semiconductor nanocrystals,” Nature 447, 441–446 (2007). Anikeeva, et al., ”Light amplification using inverted core/shell nanocrystals: towards lasing in the single-exciton regime,” J. Feldmann, ”Wave function engineering in elongated semiconductor nanocrystals with heterogeneous carrier confinement,” Nano Lett. Klimov, Nanocrystal Quantum Dots (CRC Press, Boca Raton, 2010). Hanna, Principle of Laser Engineering (Plenum Publishers, New York, 1998).
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