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

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Abstract

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% Eu3+-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@Gd2O3: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 Gd2O3:Eu microspheres (3a-f) also vary depending upon the doping ratio of Eu3+ ions.

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