Simultaneous excitation of Ce and Eu ions in Tb3Al5O12

Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) and Tb₃Al₅O₁₂:Ce³⁺ (TAG:Ce) both show the typical Ce³⁺ ion luminescence of the allowed Ce³⁺ d–f transition. Eu³⁺ codoping, however, reveals different results for both matrices: in YAG:Ce,Eu, only the luminescence of the Ce³⁺ ion occurs by excitation within the Ce³⁺ absorption bands. Here, the Eu³⁺ luminescence cannot be sensitized by the Ce³⁺ ion. But in TAG:Ce,Eu, both Ce³⁺ and Eu³⁺ luminescence are measured at several excitation wavelengths: an excitation within the Tb-sublattice results in both Ce³⁺ and Eu³⁺ luminescence, which is not surprising as an energy transfer from Tb³⁺ to Ce³⁺ and Eu³⁺ is well known in literature. In addition, an excitation in the lowest 5d level of Ce³⁺ delivers Eu³⁺ luminescence at room temperature. This means that the Ce³⁺ ion can be used as a sensitizer in the TAG lattice that transfers its energy via the Tb sublattice to the activator Eu³⁺.     

Charm in nuclei

The cooled antiproton beam at the HESR of the upcoming FAIR facility in combination with the PANDA detector will open a new comprehensive program in hadron physics. In this contribution we focus on the perspectives to study the properties of charmed hadrons in nuclear matter in antiproton-nucleus collisions. The theoretical predictions for medium modifications of mesons with both open and hidden charm are reviewed. Various proposed approaches to access their in-medium masses and widths experimentally are critically discussed. In particular, the concept to determine the J/ψ-nucleon dissociation cross section in a measurement of antiproton induced J/ψ production from different target nuclei is described. Finally, the results of first detailed simulation studies on the identification of this reaction channel in di-leptonic J/ψ decays at PANDA are presented.     

Some aspects of the polymers' electrostatic charging effects

The electrical charging of polymers is widely known and applied in many technical processes. However, the molecular and electronic reasons for this phenomenon are not fully understood. We will show that the electrical charging of polymers can be fundamentally described by their electron pair acceptor and donator properties. But polymer charging cannot only discuss on an electronic or molecular level, because during the contact of two polymer particles an enormous number of molecules of similar chemical structure coming into contact and super-molecular effects cause a charge formation. Special AFM techniques showed that oppositely charged domains can be stable side by side. Furthermore, it will be shown that the external conditions, especially the water content of the polymer and the surrounding atmosphere, have an important influence on the charge stability.     

First observation of ferromagnetism and ferromagnetic domains in a liquid metal

80 Pd₂₀ alloy below the Curie temperature T_C(l)=1257 K of the liquid state. The magnetization of the undercooled liquid sample has been measured as a function of temperature using a modified Faraday balance. Below T_C(l), the magnetization of the liquid metal shows a plateau in the weak external field of μ₀H_z=5.6 mT. The effect is comparable to the behaviour of the corresponding solid phase, indicating the onset of spontaneous magnetization with ferromagnetic domains. T_C(l) is about 20 K lower than the Curie temperature of the solid phase T_C(s). Received: 24 February 1997/Accepted: 16 May 1997