Abstract
GdPO4 hollow microspheres were synthesized by using a novel multi-step transformation synthetic route for the first time with polystyrene (PS) spheres as the template, followed by the combination of a facile homogeneous precipitation method, an ion-exchange process, and a calcination process. The XRD results indicated that the GdPO4 hollow microspheres have a pure hexagonal phase. The SEM and TEM images confirmed that the as-obtained GdPO4 hollow spheres have a uniform morphology with an average diameter of 2.7 μm and shell thickness of about 150 nm. The up-conversion luminescence properties as well as the emission mechanisms of the GdPO4:Yb3+, Ln3+ (Ln3+ = Tm3+, Er3+ and Ho3+) hollow microspheres were systematically investigated, which show blue (Tm3+, 1G4 → 3H6), green (Er3+, 4S3/2, 2H11/2 → 4I15/2), and red (Ho3+, 5F5 → 5I8) luminescence under 980 nm NIR excitation, providing potential applications in bioanalysis, optoelectronic and nanoscale devices, future color displays and light-emitting devices, and so on.
Highlights
GdPO4 hollow microspheres were synthesized by using a novel multi-step transformation synthetic route for the first time with polystyrene (PS) spheres as the template, followed by the combination of a facile homogeneous precipitation method, an ion-exchange process, and a calcination process
The SEM and transmission electron microscopy (TEM) images confirmed that the asobtained GdPO4 hollow spheres have a uniform morphology with an average diameter of 2.7 mm and shell thickness of about 150 nm
0.2 g of NH4H2PO4 dissolved in an appropriate amount of deionized water was dripped into the Scheme 1 illustrates the synthesis route for the hollow GdPO4 microspheres
Summary
Cost techniques to fabricate large-scale and well-crystallized hollow structures. Recently, rare earth orthophosphates (REPO4) have been extensively studied since their potential applications in color displays, eld-effect transistors, optoelectronics, solar cells, and light sources.[9,10,26] Among the different kinds of rare earth orthophosphates, gadolinium orthophosphate (GdPO4) is a very important host material for phosphor for Stokes shi ed luminescence and has high thermal and chemical stability because Gd3+ has a half- lled 4f electron shell with a stable structure.[27]. Because of the presence of a large number of unpaired electrons in the gadolinium ion, complex species of Gd3+ have been commonly used as MR contrast agents for positive intensity images.[31] much more efforts have been devoted to exploit state-of-the-art methods for the synthesis of GdPO4 with different morphologies such as hydrothermal reactions,[10] co-precipitation route,[32] pechini type sol–gel,[27] and solid-state reaction.[27] to the best of our knowledge, the reports on the synthesis of uniform and welldispersed Ln3+-doped GdPO4 hollow microspheres using the template method are still limited. We report a facile process for the synthesis of uniform GdPO4:Yb3+/Ln3+ (Ln3+ 1⁄4 Tm3+, Er3+, Ho3+) hollow microspheres, using urea as a precipitating agent and colloidal. Our method is economical, environmentally friendly, and conducive to high-yield mass production, which may pave the way to synthesize hollow spheres of other oxides and extend their applications
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