Bulk Functional Materials Design Using Oxide Nanosheets as Building Blocks: A New Upconversion Material Fabricated by Flocculation of Ca2Nb3O10- Nanosheets with Rare-Earth Ions

A new upconversion (UC) material was designed by flocculating a Ca2Nb3O10- nanosheet, which acts as thermal and structural stabilizer, with Ho3+ photoactivator, Yb3+ sensitizer, and Y3+ space filler. The flocculated product consists of the restacked nanosheets and the rare-earth ions in the internanosheet gallery. The restacked sheet faces of the Ca2Nb3O10- nanosheet building blocks are self-organized in a parallel manner, and their crystallographic coherency extends to three layers on average. On the other hand, the nanosheet building blocks are randomly staggered along the in-layer direction. Chemical composition of the flocculated product was estimated as (Ho(0.096)yb(0.23)Y(0.164)) Ca-1.76 square 0.24Nb3O10.1.4H(2)O. Heat treatment of the flocculated product at 500 degrees C was necessary in order to suppress nonradiative energy loss via OH vibration and to induce UC emission. Even after the heat treatment, perovskite-type atomic arrangement of the Ca2Nb3O10- nanosheet building block was retained. Upon laser irradiation at 980 nm, two UC emission bands around 550 and 660 nm were observed, and the emission was visible to the eye. The result from this study suggests that flocculation of nanosheets, as building blocks, with counterions is a promising way to design bulk functional materials that are rather difficult or impossible to prepare by conventional synthetic approaches.