Effect of Eu³⁺ Concentration on Luminescent Properties of Calcium Hydroxyapatite

Spectral and kinetic characteristics of calcium hydroxyapatite samples Ca₁₀(PO₄)₆(OH)₂ doped with Eu³⁺ ion (1, 5, and 10 mol %) were studied. The hydroxyapatite samples were presented in two forms: as-synthesized powders and heat-treated powders at 1300°C in air. Under 266 nm pulse laser excitation, they exhibited luminescence by the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions in the range of 550–750 nm. A study of luminescence decays at emission wavelengths of 574 nm (⁵D₀ → ⁷F₀ transition) and 590 nm (⁵D₀ → ⁷F₁ transition) showed a complex character of luminescence decay for as-synthesized samples and predominantly monoexponential luminescence decay for heat-treated samples. With the increase of Eu³⁺ concentration, the luminescence effective decay times for these transitions decreased for as-synthesized samples, whereas the luminescence lifetimes displayed almost the same values for the heat-treated samples.