Synthesis and photoluminescence properties of Eu³⁺-doped silica@coordination polymer core-shell structures and their calcinated silica@Gd₂O₃:Eu and hollow Gd₂O₃:Eu microsphere products

The conjugation of Eu³⁺-doped coordination polymers constructed from Gd³⁺ and isophthalic acid (H₂IPA) with silica particles is investigated for the production of luminescent microspheres. A series of doping ratio-controlled silica@coordination polymer core-shell spheres is easily synthesized by altering the amounts of metal nodes used in the reactions, where the ratios of Gd³⁺ and Eu³⁺ are 10:0 (1a), 9:1 (1b), 8:2 (1c), 7:3 (1d), 5:5 (1e), and 0:10 (1f). The formation of monodisperse uniform core-shell structures is achieved throughout the entirety of a series. Investigations of the photoluminescence property of the resulting series of silica@coordination polymer core-shell spheres reveal that 20% Eu ³⁺-doped product (1c) has the strongest emission intensity. The subsequent calcination process on the silica@coordination polymer core-shell structures (1a-f) results in the formation of a series of doping ratio-controlled silica@Gd₂O₃:Eu core-shell microspheres (2a-f) with uniform shell thickness. During the calcination step, the coordination polymers within silica@coordination polymer core-shells are transformed into metal oxides, resulting in silica@Gd₂O ₃:Eu core-shell structures. The final etching process on the silica@Gd₂O₃:Eu core-shell microspheres (2a-f) produces a series of hollow Gd₂O₃:Eu microspheres (3a-f) as a result of the elimination of silica cores. The luminescence intensities of silica@Gd₂O₃:Eu core-shell (2a-f) and hollow Gd ₂O₃:Eu microspheres (3a-f) also vary depending upon the doping ratio of Eu³⁺ ions. A series of monodisperse Eu ³⁺-doped luminescent silica@coordination polymer core-shell microspheres is synthesized through the growth of coordination polymers on silica surfaces. The doping ratio is controlled by altering the amounts of metal ions used in the reactions. The subsequent calcination and etching processes result in the formation of doping ratio-controlled luminescent silica@Gd ₂O₃:Eu core-shell and hollow Gd₂O ₃:Eu microspheres.