Structural and dielectric properties of Sr2_{2}TiO4_{4} from first principles

We have investigated the structural and dielectric properties of Sr$_{2}$TiO$_{4}$,the first member of the Sr$_{n+1}$Ti$_{n}$O$_{3n+1}$ Ruddlesden-Popper series, within density functional theory. Motivated by recent work in which thin films of Sr$_{2}$TiO$_{4}$ were grown by molecular beam epitaxy (MBE) on SrTiO$_{3}$ substrates, the in-plane lattice parameter was fixed to the theoretically optimized lattice constant of cubic SrTiO$_{3}$ (n=$\infty$), while the out-of-plane lattice parameter and the internal structural parameters were relaxed. The fully relaxed structure was also investigated. Density functional perturbation theory was used to calculate the zone-center phonon frequencies, Born effective charges, and the electronic dielectric permittivity tensor. A detailed study of the contribution of individual infrared-active modes to the static dielectric permittivity tensor was performed. The calculated Raman and infrared phonon frequencies were found to be in agreement with experiment where available. Comparisons of the calculated static dielectric permittivity with experiments on both ceramic powders and epitaxial thin films are discussed.Comment: 11 pages, 1 figure, 8 tables, submitted to Phys. Rev.

Paramagnetic inorganic nanoparticles as T1 MRI contrast agents

Magnetic resonance imaging (MRI) is one of the most powerful molecular imaging techniques and can noninvasively visualize and quantify biological processes within the living organisms. The introduction of exogenous contrast agents has allowed specific visualization of biological targets as well as enhanced the sensitivity of MRI. Recently, paramagnetic inorganic nanoparticles showing positive T1 contrast effect have been investigated as T1 MRI contrast agents. Since the first trials of spherical nanoparticles of manganese oxide and gadolinium oxide, inorganic nanoparticles of various compositions and shapes have been used for in vivo and in vitro MRI because of their distinct signal enhancement in MR images. However, for clinical applications, important and complex issues such as safety and efficiency should be investigated by active research encompassing multiple disciplines, including chemistry, biology, biomedical engineering, and medicine. © 2013 Wiley Periodicals, Inc.136421sciescopu

Mesoporous silica-coated luminescent Eu3+ doped GdVO4 nanoparticles for multimodal imaging and drug delivery

We describe a simple method for synthesizing mesoporous silica-coated luminescent europium-doped gadolinium vanadate (GdVO4:Eu3+@mSiO2) nanoparticles. Their biomedical applications as a potential imaging nanoprobe for both fluorescence imaging and magnetic resonance imaging (MRI) and as a simultaneous anti-cancer drug delivery vehicle are also discussed. Eu3+ doped GdVO4 nanoparticles exhibit strong red photoluminescence and the Gd3+ in GdVO4 can be used as a T1 contrast agent for MRI. T1-weighted MR contrast enhancement as well as sustained intracellular drug delivery can be achieved by the mesoporous silica layer coating onto a single nanoparticle. Enhanced T1 MR contrast was proven by relaxometric studies on water access to the paramagnetic core. GdVO4:Eu3+@mSiO2 nanoparticles as a new type of theragnostic (imaging and treatment) agent can provide new opportunities in a cancer treatment.114151sciescopu