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Valence Bond Theory

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Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...

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Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...

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Related Experiment Video

Updated: Nov 14, 2025

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

Published on: April 12, 2018

Excitonic Complexes in n-Doped WS₂ Monolayer.

Małgorzata Zinkiewicz¹, Tomasz Woźniak², Tomasz Kazimierczuk¹

¹Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland.

|March 8, 2021

Summary

This study reveals the origins of emission lines in n-doped tungsten disulfide (WS₂) monolayers. Researchers identified bright and dark negative trions and their phonon replicas using magnetic fields and calculations.

Keywords:

biexciton dark exciton exciton phonon replica trion tungsten disulfide monolayer

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Published on: December 20, 2016

Area of Science:

Condensed Matter Physics
Materials Science
Quantum Optics

Background:

Low-temperature photoluminescence reveals complex emission spectra in n-doped transition metal dichalcogenides.
Understanding exciton complexes in 2D materials is crucial for optoelectronic applications.

Purpose of the Study:

To identify the origin of various emission lines in n-doped WS₂ monolayer photoluminescence.
To distinguish between different types of negatively charged excitons and their properties.

Main Methods:

Low-temperature photoluminescence spectroscopy under external magnetic fields.
First-principles calculations to model electronic and optical properties.
Analysis of experimentally extracted and theoretically calculated g-factors.

Main Results:

All observed emission lines, except the neutral A exciton, originate from negatively charged excitons.
Identification of bright (singlet, triplet) and dark (spin- and momentum-forbidden) negative trions.
Distinction between semidark trions and negative biexcitons based on g-factors.

Conclusions:

Three distinct families of WS₂ exciton complexes were identified: bright, intravalley dark, and intervalley dark.
The g-factors of spin-split subbands in conduction and valence bands were determined.
This work provides a comprehensive understanding of exciton physics in WS₂ monolayers.