Effect of pre-annealing on NO32- centers in synthetic hydroxyapatite

► Effect of pre-annealing of γ- or UV- irradiated HAP on NO32- centers were analyzed. ► Pre-annealing of HAP with NO32- and CO32- does not change the parameters of NO32-. ► Pre-annealing of HAP with NO32- changes the hyperfine parameter A⊥ of NO32-. ► Two new NO32- centers in γ-irradiated HAP with NO32- were observed. ► Dependence of NO32- amount on the annealing temperature in HAP is non-monotonous.