2023-07-14 ロスアラモス国立研究所(LANL)
◆磁性ドーパントを含む量子ドットは、スピン交換相互作用によってキャリアの増殖が増強され、効率的なキャリアの増殖が実現します。特に太陽スペクトル内の光子エネルギー範囲で増強が大きく、光エネルギー変換技術への応用が期待されます。
＜関連情報＞
- https://discover.lanl.gov/news/0713-quantum-dots/
- https://www.nature.com/articles/s41563-023-01598-x
- https://www.nature.com/articles/s41565-019-0548-1
マンガン添加コロイド量子ドットにおけるスピン交換キャリア増倍 Spin-exchange carrier multiplication in manganese-doped colloidal quantum dots
Ho Jin,Clément Livache,Whi Dong Kim,Benjamin T. Diroll,Richard D. Schaller & Victor I. Klimov
Nature Materials Published:13 July 2023
DOI:https://doi.org/10.1038/s41563-023-01598-x
Abstract
Carrier multiplication is a process whereby a kinetic energy of a carrier relaxes via generation of additional electron–hole pairs (excitons). This effect has been extensively studied in the context of advanced photoconversion as it could boost the yield of generated excitons. Carrier multiplication is driven by carrier–carrier interactions that lead to excitation of a valence-band electron to the conduction band. Normally, the rate of phonon-assisted relaxation exceeds that of Coulombic collisions, which limits the carrier multiplication yield. Here we show that this limitation can be overcome by exploiting not ‘direct’ but ‘spin-exchange’ Coulomb interactions in manganese-doped core/shell PbSe/CdSe quantum dots. In these structures, carrier multiplication occurs via two spin-exchange steps. First, an exciton generated in the CdSe shell is rapidly transferred to a Mn dopant. Then, the excited Mn ion undergoes spin-flip relaxation via a spin-conserving pathway, which creates two excitons in the PbSe core. Due to the extremely fast, subpicosecond timescales of spin-exchange interactions, the Mn-doped quantum dots exhibit an up-to-threefold enhancement of the multiexciton yield versus the undoped samples, which points towards the considerable potential of spin-exchange carrier multiplication in advanced photoconversion.
スピン交換オージェ相互作用によって操作される量子ドットのホットエレクトロン・ダイナミクス Hot-electron dynamics in quantum dots manipulated by spin-exchange Auger interactions
Rohan Singh,Wenyong Liu,Jaehoon Lim,István Robel & Victor I. Klimov
Nature Nanotechnology Published:07 October 2019
DOI:https://doi.org/10.1038/s41565-019-0548-1
Abstract
The ability to effectively manipulate non-equilibrium ‘hot’ carriers could enable novel schemes for highly efficient energy harvesting and interconversion. In the case of semiconductor materials, realization of such hot-carrier schemes is complicated by extremely fast intraband cooling (picosecond to subpicosecond time scales) due to processes such as phonon emission. Here we show that using magnetically doped colloidal semiconductor quantum dots we can achieve extremely fast rates of spin-exchange processes that allow for ‘uphill’ energy transfer with an energy-gain rate that greatly exceeds the intraband cooling rate. This represents a dramatic departure from the usual situation where energy-dissipation via phonon emission outpaces energy gains due to standard Auger-type energy transfer at least by a factor of three. A highly favourable energy gain/loss rate ratio realized in magnetically doped quantum dots can enable effective schemes for capturing kinetic energy of hot, unrelaxed carriers via processes such as spin-exchange-mediated carrier multiplication and upconversion, hot-carrier extraction and electron photoemission.
