Micromolding in capillaries for calcination-free fabrication of flexible inorganic phosphor films consisting of rare-earth-ion-doped nanoparticles

Photoluminescence and Energy Transfer in Double- and Triple-Lanthanide-Doped YVO4 Nanoparticles

Optical materials doped with several lanthanides are unique in their properties and are widely used in various fields of science and technology. The study of these systems provides solutions for noncontact thermometry, bioimaging, sensing technology, and others. In this paper, we report on the demonstration of YVO₄ nanoparticles doped with one, two, and three different rare earth ions (Tm³⁺, Er³⁺, and Nd³⁺). We discuss the morphology, structural properties, and luminescence behavior of particles. Luminescence decay kinetics reveal the energy transfer efficiency (up to 78%) for different ions under the selective excitation of individual ions. Thus, we found that the energy transition from Tm³⁺ is more favorable than from Er³⁺ while we did not observe any significant energy rearrangement in the samples under the excitation of Nd³⁺. The observed strong variation of REI lifetimes makes the suggested nanoparticles promising for luminescent labeling, anticounterfeiting, development of data storage systems, etc.

Columnar Gd2O3:Eu3+/Tb3+ phosphors: preparation, luminescence properties and growth mechanism

Columnar Gd₂O₃:Eu³⁺/Tb³⁺ phosphors were successfully prepared by a solvothermal method and subsequent calcination process.

Microcrystallization of a Solution-Processable Organic Semiconductor in Capillaries for High-Performance Ambipolar Field-Effect Transistors

We report on the use of microcrystallization in capillaries to fabricate patterned crystalline microstructures of the low-bandgap ambipolar quinoidal quaterthiophene derivative (QQT(CN)4) from a chloroform solution. Aligned needle-shaped QQT(CN)4 crystals were formed in thin film microstructures using either open- or closed- capillaries made of polydimethylsiloxane (PDMS). Their charge transport properties were evaluated in a bottom-gate top-contact transistor configuration. Hole and electron mobilities were found to be as high as 0.17 and 0.083 cm(2) V(-1) s(-1), respectively, approaching the values previously obtained in individual QQT(CN)4 single crystal microneedles. It was possible to control the size of the needle crystals and the microline arrays by adjusting the structure of the PDMS mold and the concentration of QQT(CN)4 solution. These results demonstrate that the microcrystallization in capillaries technique can be used to simultaneously pattern organic needle single crystals and control the microcrystallization processes. Such a simple and versatile method should be promising for the future development of high-performance organic electronic devices.

Transparent nanophosphor films with high quantum efficiency through cold compaction

Compaction of nanophosphor coatings by means of cold isostatic pressing is shown to dramatically improve their optical and mechanical properties.

Calcination-free micropatterning of rare-earth-ion-doped nanoparticle films on wettability-patterned surfaces of plastic sheets

We demonstrate a patterning technique of rare-earth-ion-doped (RE) nanoparticle films directly on wettability-patterned surfaces fabricated on plastic sheets in one step. Self-assembled monolayers consisting of silane-coupling agent with hydrophobic groups were fabricated on plastic sheets. UV-ozone treatments were performed through a metal mask to selectively remove the self-assembled monolayers in a patterned manner, resulting in the formation of wettability-patterned surfaces on plastic sheets. Using a water dispersion of Er(3+) and Yb(3+)-codoped Y2O3 nanoparticles at a diameter of 100 nm, RE-nanoparticle films were fabricated on the wettability-patterned surfaces by a dip-coating technique. By adjusting the concentration of RE-nanoparticle dispersion, withdrawal speed, and withdrawal angle, amount of RE-nanoparticles, we were able to control the structures of the RE-nanoparticle films. Fluorescence microscope observations demonstrate that visible upconversion luminescence and near-infrared fluorescence were emitted from the RE-nanoparticle films on the wettability-patterned surfaces. This technique allows for the fabrication of flexible emitting devices with long-operating life time with minimized material consumption and few fabrication steps, and for the application to sensors, emitting devices, and displays in electronics, photonics, and bionics in the future.

Electrophoretic deposition and characterization of transparent nanocomposite films of YVO4:Bi3+,Eu3+ nanophosphor and silicone-modified acrylic resin

We fabricated nanocomposite films from an aqueous suspension of red-emitting YVO4:Bi(3+),Eu(3+) nanoparticles (hydrodynamic size: 22 ± 6 nm) and silicone-modified acrylic resin nanoparticles of (60 ± 15 nm) by electrophoretic deposition under application of a constant voltage. The nanocomposite films were formed from these negatively charged nanoparticles on ITO-coated glass substrates on the anodic side at the volume ratio of nanophosphor:resin ∼ 40:60. According to transmission electron microscopy observations, the YVO4:Bi(3+),Eu(3+) nanoparticles are well-dispersed around the resin nanoparticles. The fabricated films are transparent to the naked eye under white light because both nanoparticles show no absorption and low light scattering in the visible region. A silicone-modified acrylic resin film without the nanophosphor exhibits no absorption in the UV region (>300.0 nm). However, the fabricated nanocomposite films show near-UV absorption owing to the interband transition between the valence band and the conduction band of the YVO4:Bi(3+),Eu(3+) nanoparticles. A sharp emission peak corresponding to the (5)D0 → (7)F2 transition of Eu(3+) is observed at 619.5 nm, under 365.0 nm excitation, for each nanocomposite film. The photoluminescence intensity at 619.5 nm under 365.0 nm excitation is proportional to 1-10(-OD) (OD: optical density at 365.0 nm) for film thicknesses ≤6 μm. This is attributed to the low light scattering from both nanoparticles in the nanocomposite film. Conversely, the observed photoluminescence intensity for film thicknesses >6 μm is higher than the value expected from the proportional relationship. This suggests that the excitation of the nanophosphors efficiently occurs due to multiple scattering of excitation light.