Luminescence of Eu$^{3+}$ doped calcium hydroxyapatite and tricalcium phosphate powders

The use of calcium phosphates as a basis for prosthetic materials for musculoskeletal injuries and luminescent probes is a promising direction because these compounds correspond to the mineral composition of bone. The results of a study of the spectral and luminescence decay of Eu$^{3+}$ ions in hydroxyapatite and tricalcium phosphate matrices after synthesis and after heat treatment at 1573 K in air are discussed. A study of luminescence using a UV laser revealed lines characteristic of Eu$^{3+}$ in both materials: the $^5$D$_0\to^7$F$_0$ and $^5$D$_0\to^7$F$_2$ transitions have the highest line intensity. Heat treatment led to a change in the spectral and kinetic characteristics: a significant effect on the shape of spectral lines and lifetimes was found. The luminescence decay of the samples at a wavelength of 622.7 nm before heat treatment is biexponential, which indicates the presence of nonequivalent positions of Eu$^{3+}$ ions in the matrices. For a hydroxyapatite sample, annealing leads to the resolution of Stark components and intense luminescence at a wavelength of 573.7 nm, which indicates, the luminescence lifetime increases. For a tricalcium phosphate sample, annealing also leads to the resolution of Stark components in the luminescence spectrum, the luminescence decay becomes single-exponential with higher luminescence lifetime.