Tamarat Philippe, Bodnarchuk Maryna I, Trebbia Jean-Baptiste, Erni Rolf, Kovalenko Maksym V, Even Jacky, Lounis Brahim
Université de Bordeaux, LP2N, Talence, France.
Institut d'Optique and CNRS, LP2N, Talence, France.
Nat Mater. 2019 Jul;18(7):717-724. doi: 10.1038/s41563-019-0364-x. Epub 2019 May 13.
Lead halide perovskites have emerged as promising new semiconductor materials for high-efficiency photovoltaics, light-emitting applications and quantum optical technologies. Their luminescence properties are governed by the formation and radiative recombination of bound electron-hole pairs known as excitons, whose bright or dark character of the ground state remains unknown and debated. While symmetry analysis predicts a singlet non-emissive ground exciton topped with a bright exciton triplet, it has been predicted that the Rashba effect may reverse the bright and dark level ordering. Here, we provide the direct spectroscopic signature of the dark exciton emission in the low-temperature photoluminescence of single formamidinium lead bromide perovskite nanocrystals under magnetic fields. The dark singlet is located several millielectronvolts below the bright triplet, in fair agreement with an estimation of the long-range electron-hole exchange interaction. Nevertheless, these perovskites display an intense luminescence because of an extremely reduced bright-to-dark phonon-assisted relaxation.
卤化铅钙钛矿已成为用于高效光伏、发光应用和量子光学技术的有前景的新型半导体材料。它们的发光特性由被称为激子的束缚电子-空穴对的形成和辐射复合所支配，其基态的明亮或暗态性质仍然未知且存在争议。虽然对称性分析预测基态为单重态非发射激子，其上为明亮的激子三重态，但据预测， Rashba效应可能会颠倒明亮和暗态的能级顺序。在此，我们提供了在磁场下单晶甲脒溴化铅钙钛矿纳米晶体低温光致发光中暗激子发射的直接光谱特征。暗单重态位于明亮三重态下方几毫电子伏特处，与对长程电子-空穴交换相互作用的估计相当吻合。然而，由于明亮到暗态的声子辅助弛豫极大地减少，这些钙钛矿显示出强烈的发光。
