Absorption Spectra and Electron Vibration Coupling of Ti:Sapphire From First Principles

Abstract

Firstprinciples calculations are performed to study the absorption spectra and electronvibration coupling of titaniumdoped sapphire (Ti:Al2O3). Geometry optimization shows a local structure relaxation after the doping of Ti. Electronic band structure calculation shows that five additional dopant energy bands are observed around the band gap of Al2O3, and are attributed to the five localized d orbitals of the Ti dopant. The optical absorption spectra are then predicted by averaging the oscillator strength during a 4 ps firstprinciples molecular dynamics (MD) trajectory, and the spectra agree well with the experimental results. Electronvibration coupling is further investigated by studying the response of the ground and excited states to the Eg vibrational mode, for which a configuration coordinate diagram is obtained. Stokes shift effect is observed, which confirms the red shift of emission spectra of Ti:sapphire. This work offers a quantitative understanding of the optical properties and crystalfield theory of Tidoped sapphire. The firstprinciples calculation framework developed here can also be followed to predict the optical properties and study the electronvibration coupling in other doped materials.