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

Abstract

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 (Ho0.096Yb0.23Y0.164)­Ca1.76□0.24Nb3O10·1.4H2O. Heat treatment of the flocculated product at 500 °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.

Phase transformations during HLnTiO4 (Ln=La, Nd) thermolysis and photocatalytic activity of obtained compounds

“…Until present time perovskite-like compounds are actively studied as materials with wide range of important physical and chemical properties, such as super-conductivity [1], colossal magnetoresistance [2], ferroelectricity [3,4], catalytic and photocatalytic activity [5][6][7], thermochemical properties [8] and electrochemical properties [9]. In recent years, there has been a constant interest in using the soft chemistry methods for development of new layered perovskitelike compounds with specified physicochemical properties, as well as design of these materials based on perovskite structure [10][11][12][13][14].…”

Facile Synthesis of CsPbBr3/K4–xNb6O17 Nanocomposites with Sandwich-like and Scroll-like Heterostructures

“…A plate-like morphology can be seen from these SEM images. Red arrows in SEM images indicate the stacked KNO NSs. , Energy-dispersive X-ray spectroscopy (EDS) mapping images in Figure d–i confirmed the existence of Cs, Pb, Nb, and O elements in KNO NSs-Cs/Pb, while Figures S4c–f and S5c–f show no Cs or Pb elements in KNO NSs-Cs or KNO NSs-Pb. The yellow circles in Figure g,h indicate the signals from an impurity of KNbO 3 .…”

“…Additionally, photoluminescence (PL) tuning has also been achieved by optimizing activator selections to be incorporated into layered perovskite oxides by utilizing exfoliation-restacking processes . For example, Ozawa realized the incorporation of the guest counterions Ho 3+ , Yb 3+ , and Y 3+ into the interlayer galleries by utilizing NSs as building blocks …”

Water-Dispersible Triplet–Triplet Annihilation Photon Upconversion Particle: Molecules Integrated in Hydrophobized Two–Dimensional Interlayer Space of Montmorillonite and Their Application for Photocatalysis in the Aqueous Phase

“…It is known that the maximum catalytic activity of these narrow bandwidth photocatalysts under an optimized wavelength is lower than that of wide band gap photocatalysts, for example, pure TiO 2 due to heterometal or heteroanion doping . On the other hand, “photon upconversion techniques”, which are techniques by which long wavelength light can be converted to short wavelength light, have attracted much research attention recently. − Especially, the upconversion technique based on triplet–triplet (T–T) energy transfer and T–T annihilation (collectively called T–T interactions , ), which were first demonstrated approximately 50 years ago, has attracted the most research attention because even noncoherent lights, such as sunlight, can also be converted to shorter wavelength light. − By a combination of “photon upconversion techniques based on T–T interactions” using a single photocatalyst with a wide band gap, two incident low energy photons can be converted to one high energy photon, and this high energy photon can induce the photoexcitation of well-known photocatalysts with wide band gap and high catalytic activity (Figure b).…”