Gadolinium fluoride mesoporous microspheres: controllable synthesis, materials and biological properties

In this study, uniform gadolinium fluoride microspheres with controllable phases and structures have been synthesized for the first time by a facile ion exchange process using Gd(OH)CO₃ solid microspheres as precursors. It is found that the as-synthesized Na_xGd_yF_x+3y samples, including orthorhombic GdF₃, cubic Na₅Gd₉F₃₂ and hexagonal NaGdF₄, all consist of well dispersed microspheres with mesopores. After the conversion process, the products mainly inherit the size and shape of the precursors. Moreover, the used ethylene glycol (EG) plays a key role in the phase and structure of the final Na_xGd_yF_x+3y mesoporous spheres by impacting the etching and ion exchange process. Based on the time-dependent experiments of gadolinium fluorides, the possible formation mechanism is discussed in detail. Under 273 nm UV excitation, Na_xGd_yF_x+3y:2% Eu³⁺ shows bright red emissions due to efficient energy transfer from Gd³⁺ to Eu³⁺. Na_xGd_yF_x+3y:17% Yb³⁺/3% Er³⁺ exhibits the characteristic up-conversion (UC) emissions of Er³⁺. It is noted that the highest DC and UC emission intensities of NaGdF₄:Ln should be due to the hexagonal phase. The fluorescent Na_xGd_yF_x+3y mesoporous microspheres show obvious drug (doxorubicin hydrochloride, DOX) storage/release properties and good biocompatibility, suggesting their potential application in biomedical fields.