Interfacial Energy Transfer in Hollow Double-Shelled TiO₂:x%Eu³⁺@SiO₂:y%Tb³⁺ Nanospheres for Tissue Imaging

Abstract

In this paper, hollow double-shelled TiO2:x%Eu3+@SiO2:y%Tb3+ nanospheres (C1–Ti-x/Si-y) were fabricated using carbon spheres as hard template followed by a two-step sol–gel coating process. The results demonstrate that there is strong interaction between the inner TiO2 layer and outer SiO2 layer, which can be characterized by the high surface content of Ti–O–Si bonds. The strong interaction makes it possible to achieve efficient energy transfer from Tb3+ to Eu3+ ions through crossing the double-shelled interface. The interfacial energy transfer (IET) efficiency from Tb3+ to Eu3+ ions is strongly influenced by the doping concentration of Eu3+ ions whose maximum is determined to be 30.2%. Furthermore, the surface of inner TiO2 layer is modified by the outer SiO2 layer through this strong interaction, which significantly enhances the emission intensity and suppresses the concentration quenching of Eu3+ ions. Under 377 nm excitation, C1–Ti-x/Si-y simultaneously exhibits red and green emissions derived from Eu3+ and Tb3+ ions, respectively. Moreover, by varying the doping concentration of Tb3+ and Eu3+ ions, the luminescence color of the samples can be tuned from green to orange and red. The characterization results show that our proposed phosphors may provide potential applications in tissue imaging.

Structural Design for Controlling the Lattice Strain Relaxation Process in TiO2/SiO2 Core–Shell Nanoparticles

“…As shown in Figure S16, both the green and red emission intensities of C@Si-8@Ti-4@Si-8-500&Si-8@Ti-4@Si-8@Si-700& C@Si@Si-8@Ti-4@Si-8-700 (IET-1+IET-2) are higher than those of C@Si@Ti-4@Si-8-500&Si@Ti-4@Si-8@Si-700&Si-8@TiO 2 -4@Si@Si-700 (IET-1) and C@Si-8@Ti-4@Si-500&Si-8@Ti-4@Si@Si-700&C@Si@Si-8@Ti-4@Si-700 (IET-2) because more luminescence centers are incorporated and more excitation energy is absorbed and then transferred. The engineered materials with enhanced luminescence behavior may have hopeful potential applications, such as tissue imaging and bio-separation …”

“…Sucrose (3 g) was mixed with deionized water (30 mL), then transferred to a Teflon-lined stainless-steel autoclave and heated at 180 °C for 5 h. Subsequently, the precipitates were collected, purified by ethanol several times and then dried at 60 °C for 8 h. The obtained carbon sphere template (0.1 g) was used for the next coating process. The following two coating processes were carried out through the sol–gel method as in our previous work . 0.1 g of carbon spheres was added into 30 mL of absolute ethanol, and the mixture was ultrasonically dispersed.…”

“…Recently, remarkable progress has been achieved in the core–shell nanostructures, in which the shell can effectively suppress the surface quenching effect and further improve the overall emission intensity. − In addition, interfacial energy transfer (IET) has been realized by doping different rare earth ions into the core and shell. ,, Such an IET mechanism is verified to be an efficient strategy to manipulate the luminescence performance because it occurs among lanthanide pairs that are spatially separated, and some deleterious interactions between the energy donor and energy acceptor are minimized, such as concentration quenching caused by cross relaxation. ,, Unfortunately, due to the lattice strain, there is an apparent drawback in material selection: a small lattice mismatch is required for successful deposition of the shell on the core. , This lattice strain may induce interfacial defects, which can act as luminescence quenching centers and prevent the occurrence of IET. , To solve this problem, a successive coating process is adopted because the interfacial defects can be gradually diminished through repeated recrystallization during the coating of additional shells. , However, lattice strain energy rapidly accumulates with increasing shell thickness, and when the shell thickness exceeds a critical value, the lattice strain energy will be released in some way, causing adverse effects in the epitaxial layers. ,, For example, Nelli et al proposed that the atomic-level stress can be used to induce shape changes in nanoparticles, by either stabilizing or destabilizing specific structural types . Ferrando and Bochicchio reported a complete reconstruction of complete restructuring of the interface between the core and the shell induced by the lattice mismatch in bimetallic nanoparticles. , …”

Comparison of cellulose and chitin nanocrystals for reinforcing regenerated cellulose fibers

“…Another was the increased alignment of cellulose chains in the fiber direction. 14,54 Further increase of nanocrystal content would lead to the decrease of r b . Similar result was also observed when acetylated cellulose nanocrystals were used to reinforce cellulose acetate films.…”

“…CENC have great strength and axial elastic modulus, large specific surface area, high aspect ratio, low density, and a large number of hydroxyl side groups on the surface. 11,12 Because of these unique properties, CENC have been used as reinforcements to improve the mechanical properties of poly(vinyl alcohol) (PVA) films, 13 prolamin protein fibers, 14 cellulose acetate film, 15 biobased polyurethane, 16 poly(lactic acid) composites, 17 cellulose composites, 18,19 acrylic composites, 20 and other materials. [21][22][23] Chitin is the second most abundant natural polysaccharide and widely exists in the cuticle of insects, inner structures of invertebrates, exoskeleton of crustaceans, and cell wall of fungi.…”