Radiative Properties of Halogen Molecule-Intercalated Transition Metal Dichalcogenide Crystals
N. Siminel, L. Kulyuk,
Institute of Applied Physics, Moldova State University,
5 Academiei Str., Chișinău MD-2028, Republic of Moldova
The continuously growing interest in transition metal dichalcogenides (TMDs) [1] is driven not only by the fact that their monolayer forms, unlike the corresponding bulk materials, exhibit a direct band gap, but also by the possibility of tailoring their properties through the intercalation of various species into the van der Waals (vdW) gap [2].
Here, we present the results of systematic studies of the radiative properties of bulk TMD crystals (WS₂, 2H- and 3R-MoS₂, MoSe₂, and WSe₂) caused by the intercalation of halogen molecules (Cl₂, Br₂, and I₂). The investigated crystals were grown by the chemical vapor transport method using halogens as transport agents. Diatomic halogen molecules are unambiguously incorporated into the quasi-tetrahedral voids of the vdW gap [3], where they act as neutral centers with properties similar to those of isoelectronic impurities known to provide efficient radiative recombination in certain indirect-band-gap semiconductors.
The mechanisms of the observed radiative recombination, together with the spectral structure of the emission, including zero-phonon lines and their phonon sidebands [3,4], are analyzed. Kinetic models are proposed to describe the temperature evolution of the spectral and temporal characteristics of excitonic luminescence in different TMD compounds.
It is shown that the dimensions of the quasi-tetrahedral cavities in the vdW gap are nearly identical for all investigated TMD compounds. This opens new opportunities for incorporating halogen molecules not only into the vdW gaps of individual compounds but also at the interfaces between of different TMD layers, enabling the formation of intercalated van der Waals heterostructures.
Keywords: TMDs, intercalation, bound excitons, halogen molecules, luminescence.
References
[1] Sunny Gupta et al., Chemical Reviews, 125(2), 786 – 834 (2025).
[2] Ruijie Yang et al., Nature Reviews Chemistry, 8, 410 – 432 (2024).
[3] S. Anghel et al., Journal of Luminescence, 177, 331 – 336 (2016).
[4] N. Siminel et al., Optical Materials Express, 13, 886 – 891 (2023).