Submicron polyacrolein particles in situ embedded with upconversion nanoparticles for bioassay

We report a new surface modification approach of upconversion nanoparticles (UCNPs) structured as inorganic hosts NaYF4 codoped with Yb3+ and Er3+ based on their encapsulation in a two-stage process of precipitation polymerization of acrolein under alkaline conditions in the presence of UCNPs. The use of tetramethylammonium hydroxide both as an initiator of acrolein polymerization and as an agent for UCNP hydrophilization made it possible to increase the polyacrolein yield up to 90%. This approach enabled the facile, lossless embedment of UCNPs into the polymer particles suitable for bioassay. These particles are readily dispersible in aqueous and physiological buffers, exhibiting excellent photoluminescence properties, chemical stability, and also allow the control of particle diameters. The feasibility of the as-produced photoluminescent polymer particles mean-sized 260 nm for in vivo optical whole-animal imaging was also demonstrated using a home-built epi-luminescence imaging system

Spin Excitations in Solids from Many-Body Perturbation Theory

Collective spin excitations form a fundamental class of excitations in magnetic materials. As their energy reaches down to only a few meV, they are present at all temperatures and substantially influence the properties of magnetic systems. To study the spin excitations in solids from first principles, we have developed a computational scheme based on many-body perturbation theory within the full-potential linearized augmented plane-wave (FLAPW) method. The main quantity of interest is the dynamical transverse spin susceptibility or magnetic response function, from which magnetic excitations, including single-particle spin-flip Stoner excitations and collective spin-wave modes as well as their lifetimes, can be obtained. In order to describe spin waves we include appropriate vertex corrections in the form of a multiple-scattering T matrix, which describes the coupling of electrons and holes with different spins. The electron–hole interaction incorporates the screening of the many-body system within the random-phase approximation. To reduce the numerical cost in evaluating the four-point T matrix, we exploit a transformation to maximally localized Wannier functions that takes advantage of the short spatial range of electronic correlation in the partially filled d or f orbitals of magnetic materials. The theory and the implementation are discussed in detail. In particular, we show how the magnetic response function can be evaluated for arbitrary k points. This enables the calculation of smooth dispersion curves, allowing one to study fine details in the k dependence of the spin-wave spectra. We also demonstrate how spatial and time-reversal symmetry can be exploited to accelerate substantially the computation of the four-point quantities. As an illustration, we present spin-wave spectra and dispersions for the elementary ferromagnet bcc Fe, B2-type tetragonal FeCo, and CrO2 calculated with our scheme. The results are in good agreement with available experimental data