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

4d 1 (Mo 5+ ) and 5d 1 (W 5+ ) impurities doped into nonlinear optical crystals KTiOPO 4 (KTP) can occupy the inequivalent Ti1 and Ti2 sites and exhibit orthorhombically compressed octahedral n d 1 ( 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 n d 1 probes. This work stresses on the theoretical studies of the EPR parameters ( g factors g x , g y , g z and hyperfine structure constants A x , A y , A z ) and local distortions for the above n d 1 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 Mo 5+ centre I and W 5+ centres II and III, respectively, which are larger than those of host Ti1 and Ti2 sites. [ABSTRACT FROM AUTHOR]