Studies of the local distortions for nd1 (Mo5+ and W5+) impurities in KTP crystals

Abstract

4d1 (Mo5+) and 5d1 (W5+) impurities doped into nonlinear optical crystals KTiOPO4 (KTP) can occupy the inequivalent Ti1 and Ti2 sites and exhibit orthorhombically compressed octahedral nd1 (n=4, 5) centres arising from the Jahn–Teller effect. Closely relevant to the electronic levels as well as optical and magnetic properties of these materials, the above local distortions can be suitably reflected by the anisotropic electron paramagnetic resonance (EPR) signals with the paramagnetic nd1 probes. This work stresses on the theoretical studies of the EPR parameters (g factors gx, gy, gz and hyperfine structure constants Ax, Ay, Az) and local distortions for the above nd1 impurity centres in a consistent way. The local distortions are characterised by the relative axial compression ratios ρ (≈0.040, 0.032 and 0.031) and the relative planar bond length variation ratios τ (≈0.030, 0.015 and 0.012) for Mo5+ centre I and W5+ centres II and III, respectively, which are larger than those of host Ti1 and Ti2 sites.