Characterization and optical properties of cobalt-doped β-tricalcium phosphate nanoparticles: Microwave refluxing and high-temperature sintering

<jats:p>This study investigates the synthesis, characterization, and optical

properties of cobalt-doped ?-tricalcium phosphate (Co-?TCP) nanoparticles

prepared via microwave refluxing and sintered at 1000?C for 2 hours.

Incorporating Co2+ ions into the ?TCP structure significantly influences its

microstructural and optical properties. X-ray diffraction analysis (XRD)

reveals a contraction of the crystal lattice upon Co2+ doping, attributed to

the substitution of larger Ca2+ ions (ionic radius 0.099 nm) with smaller

Co2+ ions (ionic radius 0.074 nm). This reduces lattice parameters, cell

volume, crystallinity, and smaller crystallite sizes. The degree of

crystallinity decreases from 89.56% for pure ?-TCP to 57.81% for 3Co-?-TCP.

Scanning electron microscopy (SEM) shows that Co2+ doping produces more

homogeneous powder with enhanced interconnectivity while maintaining a

spheroidal agglomerated structure. The average particle size decreases from

approximately 300 nm for pure ?TCP to 246 nm for 3Co-?TCP. Fourier transform

infrared spectroscopy confirms the successful integration of Co2+ ions into

the ?TCP lattice, evidenced by peak broadening and intensity reduction.

Notably, incorporating Co2+ ions induces a striking colour change from white

to pink, with intensity proportional to cobalt concentration. UV-Vis

spectroscopy reveals characteristic absorption peaks at 530 and 678 nm,

associated with Co2+ electronic transitions. The unique optical properties

of Co2+ ions doped in ?TCP open up new possibilities for its use in

bioimaging and drug delivery systems</jats:p>