Synthesis of porous upconverting luminescence α-NaYF4:Ln(3+) microspheres and their potential applications as carriers.

The present work reports a self-sacrificing template strategy to synthesize porous α-NaYF4 microspheres via the reaction of as-prepared Y(OH)CO3·H2O@SiO2 with NH4F and NaNO3 solutions. XRD, SEM, TEM and N2 adsorption-desorption measurements were used to characterize the resulting product. The surface SiO2 shell was shown to play a vital role in size and shape control and porosity formation. A possible reaction mechanism was explored in terms of a surface-protected etching and ion-exchange reaction process. To explore their application potential, the storage and release behavior of Rhodamine 640 dye in the porous α-NaYF4 microspheres was investigated, showing a relatively high loading efficiency and a sustained release ratio. Under near-infrared (NIR) irradiation, porous α-NaYF4 microspheres doped with lanthanide ions showed typical upconverting luminescence characteristics that can convert NIR photons to ultraviolet/visible photons. The above features and properties indicate that our present porous upconverting luminescence particles are promising in biological applications as luminescence imaging agents and drug carriers.