Inhomogeneous broadening of electron-paramagnetic-resonance and optical spectra of V4+ in CaYAlO4

Analysis on the local structures for 3d1 impurities (Ti3+ and V4+ ) in KTiPO4

Making use of the perturbation formulae for 3d¹ ions (Ti³⁺ and V⁴⁺ ) under orthorhombically compressed octahedra, the spin Hamiltonian parameters (g factors: g_x , g_y , g_z and hyperfine structure constants: A_x , A_y , A_z ) and local structures of the 3d¹ impurity centres C₁ , C₂ , and C₃ in KTiOPO₄ crystals are theoretically analyzed in a consistent way. The remarkable local distortions (i.e., the relative axial compression ratios 11.2%, 7.0%, and 5.5% along Z axis and the relative planar bond length variation ratios 15.9%, 7.0%, and 6.0%) are obtained for the [Ti2O₆ ]^9- cluster on Ti2 site and [VO₆ ]^8- clusters on Ti1 and Ti2 sites, respectively, in view of the Jahn-Teller effect. The above local orthorhombic distortion parameters in the impurity centres are found to be more significant than the host Ti1 and Ti2 sites in pure KTiOPO₄ . The sequences (C₁  > C₂  > C₃ ) of the local orthorhombic distortion parameters ρ and τ are in accordance with those of the axial and perpendicular anisotropies Δg and δg of g factors, respectively.

Investigations on the defect structures and the g factors for the two orthorhombic Ti3+ centers in CaYAlO4

The defect structures and the g factors for the two orthorhombic Ti(3+) centers (A and B) in CaYAlO(4) are theoretically investigated from the perturbation formulas of the g factors g(xi), g(eta) and g(xi) for a 3d(1) ion in orthorhombically distorted octahedra. The centers may be attributed to Ti(3+) locating on the Al(3+) site associated with one nearest-neighbouring oxygen vacancy (V(O)) along the z (or c) axis and additional next-nearest-neighbouring Ti(4+) replacing the host Al(3+) (Ti(Al), i.e., center A) or Al(3+) vacancy (V(Al), i.e., center B) perpendicular to the c axis, respectively. Due to the electrostatic interactions arising from the local charge mismatch, the central Ti(3+) undergoes a large displacement DeltaZ away from the V(O) in the c axis, while the ligand O(2-) intervening in the Ti(3+) and Ti(Al) (or V(Al)) suffers a small outward (or inward) shift DeltaX in the corresponding c plane related to the center of oxygen octahedron. The theoretical g factors for both centers based on the above displacements are in reasonable agreement with the observed values.

Long fluorescence lifetime of Ti3+-doped low silica calcium aluminosilicate glass

This Letter reports the formation of Ti3+ in OH- free aluminosilicate glass melted under vacuum condition, with a very long lifetime (170 micros) and broad emission band shifted towards the visible region. This lifetime value was attributed to the trapping of the excited electrons by the glass defects and detrapping by thermal energy, and it is 2 orders of magnitude higher than those published for Ti3+ doped materials. Our results suggest that this glass is a promising system to overcome the challenge of extending the spectral range of traditional tunable solid state lasers towards the visible region.