Dynamic Control of Photoluminescence for Self‐assembled Nanosheet Films Intercalated with Lanthanide Ions by Using a Photoelectrochemical Reaction

Abstract

Semiconductor oxide nanosheets synthesized by exfoliation of layered oxides are two-dimensional crystals with a thickness of about 1 nm. [1][2][3][4] New layered materials and their films can be reassembled by electrostatic self-assembly deposition (ESD) [5] and by layer-by-layer (LBL) [6][7][8] techniques, respectively. Since the nanosheets have a negative charge in aqueous solution they can be used with various cationic species as the starting materials. Layered materials prepared from nanosheets and lanthanide (Ln) ions are promising as new functional materials because Ln ions have unique properties, such as luminescence and magnetic properties, that are attributable to the 4f electron orbital. For example, the titanate layered oxide intercalated with Eu 3+ ions prepared from titanate nanosheets and Eu 3+ ions has unique luminescence properties. [9][10][11] The layered oxide gives a red emission from the Eu 3+ ions which is induced by energy transfer through excitation of the bandgap of the titanate nanosheet, [9,10] and the emission from the Eu 3+ ions is promoted by intercalated water molecules.[10] Furthermore, spectral hole burning caused by the intercalated water molecules was observed in the excitation spectra at room temperature. [11] Nanosheets of TiO x , NbO x , and TaO x give a high photocurrent during the photoelectrochemical reaction under UV illumination with an energy higher than that of the bandgap. [12] This finding indicates that a large charge separation is produced between the holes in the valence band and the electrons in the conduction band during excitation of the bandgap. Consequently, layered oxide materials intercalated with Ln ions simultaneously exhibit both photoluminescence and a photoelectrochemical reaction during excitation of the bandgap on illumination with UV light. The study reported herein demonstrates a new form of dynamic control over the photoluminescence of Ln ions intercalated in self-assembled nanosheet films of TiO x and NbO x . The photoluminescence properties of Ln ions are changed by factors such as a change in the pH value and the addition of anionic species. [13][14][15][16][17] However, it is difficult to dynamically control the photoluminescence properties of Ln 3+ ions. In the present system, the emission intensities of the intercalated Eu 3+ and Tb 3+ ions can be readily controlled by varying the applied potential.The Figure S-1 in the Supporting Information). Figure 1 shows a schematic illustration of the system used for the measurement of the photoluminescence. The photoelectrochemical cell with three electrodes, with the nanosheet/Ln 3+ film acted as a working electrode, was placed in the sample chamber of a fluorescence spectrophotometer. A 0.1m K 2 SO 4 solution (pH 6.5) was used as the electrolyte solution. Figure 2 shows the emission intensities of the TiO/Eu and NbO/Tb films under illumination by UV light (wavelength: 260 nm) as a function of potential (sweep rate: 20 mV s À1 ). The red emission of the Eu 3+ ions (614 nm, 5 D 0 -7 F 2 ) appeared in...

Synthesis and photoluminescence properties of layered oxides intercalated with Eu3+ions by electrostatic self-assembly method using oxide nanosheets

“…Thus, electrons and holes produced by the band gap excitation migrate in the host layer and easily move into the interlayer to be trapped by the Eu 3+ cations. The conduction band level of TiO 2-δ nanosheet is lower than that of Nb 6 O 17 nanosheets [24], and higher than the light-emitting level of Eu 3+ [22,23].Thus, the lightemitting level of Eu 3+ is closer to the conduction band level of TiO 2-δ nanosheet than that of Nb 6 O 17 nanosheets. The weak emission intensity of Eu/NbO is presumably due to the large energy gap between conduction band level and light-emitting level of Eu 3+ .…”

“…This behavior suggests that lanthanide cations in the interlayer of the TiO 2-δ -type nanosheets might result in strong emission under the excitation of TiO 2-δ -type nanosheets. Actually, several reports on luminescence properties of the nanosheet-based layered oxides have been reported [22][23][24].…”

Aluminum assisted electrodeposition of europium in LiCl–KCl molten salt

“…Among Ln elements, Eu has been extensively studied due to its spectroscopic and electrochemical properties [20] as well as its photoluminescence [21]. Eu is also one of the fission products which is difficult to be separated from An [9].…”

Crystal structures and luminescent properties of lanthanide nitrate coordination polymers with structurally related amide type bridging podands

“…The applications of the lanthanide complexes in luminescent sensing and imaging technology, and as contract agents for MRI are very well established [5][6][7][8][9][10]. Among the luminescent complexes studied, europium(III) and terbium(III) complexes appear to be the most attractive in view of the high photoluminescent (PL) efficiency and the narrow band red/greenemission ability, which may exploited in the full-color displays [11][12][13][14] and a variety of applications ranging from chemosensors for bioactive species to active components in time resolved assays.…”