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Lu3Al5O12 (LuAG) doped with Ce3+ is a promising scintillator material with a high density and a fast response time. The light output under x-ray or y-ray excitation is however well below the theoretical limit. In this paper the influence of co-doping with Tb3+ is investigated with the aim to increase the light output. For singly doped LuAG (with Ce3+ or Tb3+) high resolution spectra are reported giving insight in the energy level structure of the two ions in LuAG. For Ce3+ zero-phonon lines and vibronic structure is observed for thetwo lowest energy d-bands and the Stokes shift (2350 cm-1) and Huang-Rhys coupling parameter (S = 9) have been determined. For Tb3+ transition to the high spin (HS) and low spin (LS) states are observed (including a zero-phonon line and vibrational structure for the highspin state). The HS-LS splitting is 5400 cm-1 which is smaller thanusually observed and is explained by a reduction of the d-f exchangecoupling parameter J by covalency. Upon replacing the smaller Lu3+ion with the larger Tb3+ ion, the crystal field splitting for the lowest d-states increases and the Ce3+ emission shows a redshift, causing the lowest d-state to shift below the 5D4 state of Tb3+ and allowing for efficient energy transfer from Tb3+ to Ce3+ down to the lowest temperatures. Luminescence decay measurements confirm efficientenergy transfer from Tb3+ to Ce3+ and provide a qualitative understanding of the energy transfer process. Co-doping with Tb3+ does not result in the desired increase in light output and an explanation based on electron trapping in defects is discussed.

In non-steady-state experiments, the electrical response of devicesbased on disordered organic semiconductors often shows a large transient contribution due to relaxation of the out-of-equilibrium charge-carrier distribution. We have developed a model describing this process, based only on the parameters describing the d.c. mobility andon Monte Carlo calculations of the effective conduction energy level. The model successfully predicts the relaxation-enhancement of thedifferential capacitance of sandwich-type devices based on a polyfluorene-copolymer. Generalization of the approach is expected to enable efficient modeling of relaxation effects in other types of experiments.

From a numerically exact solution of the Master equation for hoppingtransport in a disordered energy landscape with a Gaussian densityof states, we determine the dependence on temperature, carrier density, and electric field of the charge carrier mobility. Experimentalspace-charge limited currents in semiconducting polymer-based devices are excellently reproduced with this unified description of the mobility. At room temperature it is mainly the dependence on carrier density that plays an important role, whereas at low temperatures andhigh fields the electric field dependence becomes important. Omission of the carrier-density dependence has led to an underestimation of the hopping distance and the width of the density of states in these polymers.

The off-axis motion of particles actuated by axial magnetic or gravitational forces is studied in fluidic channels. Single actuated superparamagnetic micro-particles starting from channel walls travel towards the channel center and show unforeseen reversionary rotation phenomena. Different stages of co- and counter-rotation are observed in both micro- and macro-scale experiments and are analyzed by meansof numerical fluid-dynamics models. The related microfluidic near-surface mixing performance of the rotating actuated particles is discussed.

We present a scaling theory for charge transport in molecular semiconductors with Gaussian energy disorder, which extends standard percolation theory by including bonds with conductances close to the percolating one in the random-resistor network of bonds representing charge hopping. A general and compact expression is given for the charge mobility as a function of temperature and charge concentration, with parameters that are determined for Miller-Abrahams and Marcus hopping on different lattices from numerically exact results. A universal dependence on charge concentration is found and a temperature dependence that differs significantly from other reports.