Ab-initio studies of the electronic and optical properties of Al2O3:Ti3+ laser crystals

The structural and electronic properties of pure and Ti3+-doped alpha-Al2O3 were calculated in the present paper by using the first-principles methods. Special attention has been paid to the location of the Ti3+ states (3d(1) electron configuration) in the band gap; the lowest 3d states are at about 4.78 eV above the top of the valence band. The crystal field strength 10Dq at the Ti3+ site was estimated from the density of states diagrams to be about 17,700 cm(-1). The structural optimization of the unit cell was also performed at elevated hydrostatic pressure in the range from 0 to 25 GPa. By application of the Murnaghan equation to the obtained results, the bulk modulus of alpha-Al2O3 was estimated to be 225.69 GPa. In addition, from the analysis of the Ti3+ 3d density of states the distance dependence of the crystal field strength was found to be described by the following function: 10Dq=61.744/R-4.671, where R is expressed in A and 10Dq in eV.