Gadolinium−Europium Carbonate Particles: Controlled Precipitation for Luminescent Biolabeling

Europium-doped gadolinium carbonates particles have been prepared via urea-assisted precipitation. The reaction has been followed step by step with the investigations of the precipitate by transmission electron microscopy and wide-angle X-ray scattering, in relation with infrared absorption and thermal analyses. It has been observed that spherical particles of (Gd 0.95 Eu 0.05 )(OH)CO 3, monodispersed in size and amorphous, precipitate first and then transform to agglomerated platelike crystals of (Gd 0.95 Eu 0.05 ) 2 (CO 3 ) 3 ·2H 2 O as the precipitation continues. The Eu 3+ 5 D 0 → 7 F J emission spectrum and the 5 D 0 lifetime in the two carbonate matrices have been measured. Selected hydroxycarbonate nanoparticles (NPs), with diameters of 164 ± 20 nm, have been then transformed to oxide NPs having the cubic crystalline structure C-(Gd 0.95 Eu 0.05 ) 2 O 3, with the same shape and size. The photoluminescence (PL) properties of hydroxycarbonate and oxide NPs, and of their colloidal suspensions in water, have been investigated. The hydroxycarbonate and the oxide NPs exhibit same PL intensities when excitation is achieved in one of the Eu 3+ (4f 6 ) levels. Tests of in vitro fluorescence imaging have been performed. The luminescent NPs have been observed after their internalization by human cervical carcinoma (HeLa) cells. It is concluded that the controlled (urea-assisted) precipitation is appropriate to synthesize Gd(OH)CO 3:Eu 3+ and Gd 2 O 3:Eu 3+ nanoparticles having adequate characteristics for biolabeling.