First‐Principle Study of Bandgap Engineering and Optical Properties of Monolayer WSe₂ in Second Near‐Infrared Windows

Abstract

Fluorescence imaging in the second near‐infrared II (NIR‐II) window is opening up new possibilities in bioimaging due to its low scattering rate within the tissue. The integration of 2D materials with NIR‐II fluorescence will enable the development of multifunctional imaging probes. However, there are very few 2D materials that can fluoresce in the NIR‐II range. Monolayer WSe2 is a potential 2D material, but its photoluminescence (PL) around 790 nm is still far from the NIR‐II range due to its bandgap of 1.54 eV. In this study, it is investigated the electronic structures, dielectric functions, and PL spectra for Te, I, and Cr‐doped monolayer WSe2, as well as W and S vacant monolayer WSe2. Most of the defected monolayer WSe2 remain semiconductors, except for a few configurations exhibiting metallic properties after making vacancies. Among the monolayer WSe2 under investigation, the Cr‐doped WSe2 performs the best, exhibiting a strong PL peak in NIR‐II with a decreased bandgap around 1.0 eV. As increasing Cr concentration, the peak shifts further toward the red end of the spectrum due to an enhancement of p–d transition. The results provide a useful guideline for material synthesis applied in NIR‐II bioimaging and other biophysics.

Atomic insight into the effects of precursor clusters on monolayer WSe2

“…16–18 When the layer thickness of WSe 2 is reduced to monolayer, an indirect-to-direct band gap transition is observed. 19,20 WSe 2 has large exciton binding energies, 21–23 large carrier mobility, 24–26 and large absorption coefficients in the range of infrared to visible region, 27–29 which are promising in the field of photonics, optoelectronics, and photodetectors. In addition, WSe 2 has excellent catalytic performance.…”