Identification of Semiconductor Nanocrystals with Bright Ground-State Excitons

While nanoscale semiconductor quantum dots provide versatile fluorescent materials for light-emitting devices, their emission is partially inhibited by the “dark exciton”—the optically inactive ground state into which excitons often relax before emitting [1]. Recently, a theoretical mechanism was discovered that can potentially defeat the dark exciton. It was shown that the Rashba effect can invert the order of the lowest-lying levels, creating a bright excitonic ground state [2]. To identify materials that exhibit this behavior, here we perform an extensive high-throughput computational search of two large open-source materials databases. Based on a detailed understanding of the Rashba mechanism, we define proxy criteria and screen over 500,000 solids, generating 173 potential “bright-exciton” materials [3]. We then refine this list with higher-level first-principles calculations to obtain 28 candidates. To confirm the potential of these compounds, we select five and develop detailed effective-mass models to determine the nature of their lowest-energy excitonic state. We find that four of the five solids (BiTeCl, BiTeI, Ga₂Te₃, and KIO₃) can yield bright ground-state excitons, illustrating the power of combining physical understanding with high-throughput techniques. Our approach reveals several classes of semiconductor nanostructures with very bright emission that have not been previously synthesized, paving the way for brighter and more efficient optoelectronic devices.

[1] M. Nirmal, D. J. Norris, M. Kuno, M. G. Bawendi, Al. L. Efros, and M. Rosen, Observation of the “Dark Exciton” in CdSe Quantum Dots, Phys. Rev. Lett. 75, 3728 (1995).

[2] M. A. Becker et al., Bright Triplet Excitons in Caesium Lead Halide Perovskites, Nature 553, 189 (2018).

[3] M. W. Swift, P. C. Sercel, A. L. Efros, J. L. Lyons, and D. J. Norris, Identification of Semiconductor Nanocrystals with Bright Ground-State Excitons, ACS Nano 18, 19561 (2024).