Absorption spectra of doped Ca3(VO4)2 : Co crystals for (a) E||C and (b) E⊥C orientations: а: (1, 2) Ca3(VO4)2 : 1 and 2% Co3O4, respectively, Cz-grown; (3–5) Ca3(VO4)2 : 2 % Co3O4, open zone diffusion annealing at (3) 1150, (4) 1200 and (5) 1250 °C for 24 h; (6) Ca3(VO4)2 : 2 % Co3O4, open zone diffusion annealing at 1300 °C for 32 h; (7) diffusion from Co3O4, 24 h, 1300 °С; b: (1, 2) Ca3(VO4)2 : 1 and 2 % Co3O4, respectively, Cz-grown; (3–5) Ca3(VO4)2 : 2% Co3O4, open zone diffusion annealing at (3) 1150, (4) 1200 and (5) 1250 °C for 24 h; (6) diffusion from Co3O4, 24 h, 1300 °С