One-step microwave synthesis of (Gd, Eu)PO4 urchin-like hollow spheres: Enhanced luminescence and pH-sensitive drug delivery properties

Urchin-like hollow spheres (ULHS) with internal cavities and functional shells are critical for many applications such as drug delivery, catalysis and energy storage. We synthesized in this work the hexagonal structured (h-) (Gd, Eu)PO4 ULHS by a simple microwave method in the absence of any templates or surfactants in the reaction system, and the effects of subsequent calcination on the structure and morphology of the samples were investigated in detail. The products were formed by controlled aggregation and subsequent oriented growth of the (Gd, Eu)PO4 primary nanoparticles, and the average diameter of the sphere decreases with increasing Eu3+ incorporation. The mechanism of morphology evolution with the variation of reaction time, SO42-/RE3+ molar ratio, and pH value was also unveiled. Nitrogen adsorption-desorption measurement suggests the presence of mesopores (∼20 nm) in the ULHS. The integrated emission intensity of Eu3+ in h-(Gd0.90Eu0.10)PO4 ULHS is ∼1.5 times higher than that in nanorods (NR) benefit from the unique configuration of the coarse shell. Moreover, the h-(Gd0.90Eu0.10)PO4 ULHS exhibit sustained drug release behaviors, and a pH-sensitive drug-release pattern can be well achieved by changing the pH of the release medium. The facile synthesis strategy and the excellent performance of the h-(Gd0.90Eu0.10)PO4 ULHS may be of great significance for the preparation and application of other inorganic hollow spheres.