Pandya Raj, Steinmetz Violette, Puttisong Yuttapoom, Dufour Marion, Chen Weimin M, Chen Richard Y S, Barisien Thierry, Sharma Ashish, Lakhwani Girish, Mitioglu Anatolie, Christianen Peter C M, Legrand Laurent, Bernardot Frédérick, Testelin Christophe, Chin Alex W, Ithurria Sandrine, Chamarro Maria, Rao Akshay
Cavendish Laboratory , University of Cambridge , J.J. Thomson Avenue , CB3 0HE Cambridge , United Kingdom.
Sorbonne Université CNRS-UMR 7588, Institut des NanoSciences de Paris , INSP, 4 place Jussieu , F-75005 Paris , France.
ACS Nano. 2019 Sep 24;13(9):10140-10153. doi: 10.1021/acsnano.9b03252. Epub 2019 Sep 16.
Heterostructured two-dimensional colloidal nanoplatelets are a class of material that has attracted great interest for optoelectronic applications due to their high photoluminescence yield, atomically tunable thickness, and ultralow lasing thresholds. Of particular interest are laterally heterostructured core-crown nanoplatelets with a type-II band alignment, where the in-plane spatial separation of carriers leads to indirect (or charge transfer) excitons with long lifetimes and bright, highly Stokes shifted emission. Despite this, little is known about the nature of the lowest energy exciton states responsible for emission in these materials. Here, using polarization-controlled, steady-state, and time-resolved photoluminescence measurements, at temperatures down to 1.6 K and magnetic fields up to 30 T, we study the exciton fine structure and spin dynamics of archetypal type-II CdSe/CdTe core-crown nanoplatelets. Complemented by theoretical modeling and zero-field quantum beat measurements, we find the bright-exciton fine structure consists of two linearly polarized states with a fine structure splitting ∼50 μeV and an indirect exciton Landé -factor of 0.7. In addition, we show the exciton spin lifetime to be in the microsecond range with an unusual magnetic field dependence. The discovery of linearly polarized exciton states and emission highlights the potential for use of such materials in display and imaging applications without polarization filters. Furthermore, the small exciton fine structure splitting and a long spin lifetime are fundamental advantages when envisaging CdSe/CdTe nanoplatelets as elementary bricks for the next generation of quantum devices, particularly given their ease of fabrication.
异质结构二维胶体纳米片是一类材料，由于其高光致发光产率、原子级可调节厚度和超低激光阈值，在光电子应用中引起了极大的兴趣。特别令人感兴趣的是具有II型能带排列的横向异质结构核壳纳米片，其中载流子的面内空间分离导致具有长寿命和明亮、高斯托克斯位移发射的间接（或电荷转移）激子。尽管如此，对于这些材料中负责发射的最低能量激子态的性质却知之甚少。在这里，我们使用偏振控制的稳态和时间分辨光致发光测量，在低至1.6 K的温度和高达30 T的磁场下，研究了典型的II型CdSe/CdTe核壳纳米片的激子精细结构和自旋动力学。通过理论建模和零场量子拍频测量的补充，我们发现亮激子精细结构由两个线性偏振态组成，精细结构分裂约为50 μeV，间接激子朗德因子为0.7。此外，我们表明激子自旋寿命在微秒范围内，具有不寻常的磁场依赖性。线性偏振激子态和发射的发现突出了此类材料在无需偏振滤光片的显示和成像应用中的使用潜力。此外，当将CdSe/CdTe纳米片设想为下一代量子器件的基本构建单元时，小的激子精细结构分裂和长的自旋寿命是其基本优势，特别是考虑到它们易于制造。
