Charge Trapping Process in Photoexcited Nitrogen-Doped Titanium Oxides

Area of Science:

• Materials Science
• Solid State Physics
• Computational Chemistry

Background:

• Photoexcitation in semiconductors like titanium oxide can induce structural changes.
• Nitrogen doping (N-TiO2) is explored for modified electronic and optical properties.
• Understanding charge trapping mechanisms is crucial for photocatalysis and device applications.

Purpose of the Study:

• To investigate structural modifications in N-TiO2 post-photoexcitation.
• To identify charge trapping sites and their impact on Ti K-edge EXAFS spectra.
• To elucidate the dynamics of charge trapping under UV and visible light.

Main Methods:

• First-principles calculations (e.g., Density Functional Theory).
• Simulation of charge trapping phenomena and structural distortions.
• Comparison of predicted K edge Extended X-ray Absorption Fine Structure (EXAFS) spectra with experimental data.

Main Results:

• Charge trapping is localized near oxygen vacancy (O-vac) sites.
• O-vac significantly influences EXAFS spectra; substitutional N doping near O-vac has minimal spectral impact.
• UV-excited electrons migrate within O-vac sites (~300 ps).
• Visible light-excited electrons (N 2p → Ti 3d) are rapidly trapped at N-adjacent O-vac sites (~1 ps).

Conclusions:

• Oxygen vacancies are key sites for charge trapping in N-TiO2.
• Distinct charge trapping dynamics are observed under UV versus visible light excitation.
• The findings provide insights into the electronic structure and excited-state behavior of N-TiO2.