Coloured Synthetic zircon crystals. Flux growth and EPR of V4+ impurity centres

The growth of blue and green zircon (ZrSiO4) crystals from fluxes consisting of (PbO + V2O5) and (3 Bi2O3 + V2O5), respectively, is reported. Vanadium is found in the crystals and EPR experiments show that it occurs, at least in part, as V4+ in sites of tetragonal symmetry. EPR is observed at X-and Q-band frequencies at temperatures of 20 and 4.2 K. The hyperfine constants are anisotropic and A‖ shows a marked temperature dependence. The spin Hamiltonian parameters at 20 K are g⊥ = 1.8930 ± 0.0008, A‖ = (81.6 ± 0.2) × X 10−4 cm−1, g⊥ = 1.9699 ± 0.0008, A‖ = (28.9 ± 0.2) × 10−4 cm−1. At 4.2 K: A‖ = (84.1 ± 0.2) × 10−4 cm−1.