Spectroscopic Properties of Cobalt Ions in Ca₃(VO₄)₂ Crystals Doped via Thermal Diffusion and During Synthesis

The spectroscopic properties of cobalt ions in Ca 3 (VO 4 ) 2 crystals doped via thermal diffusion and during synthesis are investigated. The diffusion doped crystal shows the potential for higher cobalt doping while maintaining its high initial optical quality. The redistribution of several absorption and fluorescence lines intensities with cobalt concentration is attributed to the formation of Co 2+ optical centers with sufficiently different local environments. The fluorescence decay times of Co 2+ optical centers are measured to differ by an order of magnitude (95 and 13 μs) and are attributed to centrosymmetric M1 and low symmetry M2 types of Co 2+ optical centers, possibly corresponding to Ca(4) and Ca(1) positions of Ca 3 (VO 4 ) 2 crystal, respectively. Nonlinear transmission of Co 2+ M2 centers is measured, and efficient absorption cross‐sections of 1.4 × 10 −19 and 2.4 × 10 −19 cm 2 are evaluated at 1300 and 1500 nm, respectively. The narrow fluorescence line of cobalt ions peaking at about 1170 nm, detected in both Ca 3 (VO 4 ) 2 crystals doped via thermal diffusion and during synthesis, is attributed to Co ions in a trivalent state.