Intrinsically directional light emitters are potentially important for applications in photonics including lasing and energy-efficient display technology. Here, we propose a new route to overcome intrinsic efficiency limitations in light-emitting devices by studying a CdSe nanoplatelets monolayer that exhibits strongly anisotropic, directed photoluminescence. Analysis of the two-dimensional k-space distribution reveals the underlying internal transition dipole distribution. The observed directed emission is related to the anisotropy of the electronic Bloch states governing the exciton transition dipole moment and forming a bright plane. The strongly directed emission perpendicular to the platelet is further enhanced by the optical local density of states and local fields. In contrast to the emission directionality, the off-resonant absorption into the energetically higher 2D-continuum of states is isotropic. These contrasting optical properties make the oriented CdSe nanoplatelets, or superstructures of parallel-oriented platelets, an interesting and potentially useful class of semiconductor-based emitters.

本质上定向的发光体对于包括激光和节能显示技术在内的光子学应用具有潜在的重要性。在这里，我们提出了一种新的途径，通过研究表现出强各向异性，定向光致发光的CdSe纳米片单层，来克服发光器件的固有效率限制。二维k的分析空间分布揭示了潜在的内部跃迁偶极子分布。观察到的定向发射与支配激子跃迁偶极矩并形成亮平面的电子布洛赫态的各向异性有关。垂直于血小板的强定向发射通过状态和局部场的光学局部密度进一步增强。与发射方向相反，进入能量较高的2D连续态的非共振吸收是各向同性的。这些不同的光学特性使定向CdSe纳米片或平行定向片的超结构成为一类有趣且潜在有用的基于半导体的发射器。