Algebraic curvature tensors which are Osserman-IP in the (− − + +)-signature setting are completely determined. As a consequence, it is shown that a fourdimensional pointwise Osserman-IP manifold is a space of constant sectional curvature or, otherwise, at each point the Jacobi operators either vanish or they are two-step nilpotent.

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Zn,-,Mn,Se ( 0 . 0 1 6 ~~~0 . 4 4 5 ) shows luminescence emission not only in the yellow spectral range ("T,+6A,) but also in the near infrared. The excitation spectra of the yellow and of the infrared band are compared at different concentrations x and different temperatures T. Both emission bands are connected by energy transfer. While the yellow emission is well described by a transition within the 3d shell of tetrahedrally coordinated Mn2+ the nature of the infrared emission is not yet clear.

The luminescence excitation and emission spectra of Znl -,Mn,S with high Mn concentration (0.01 2 x 5 0.25) is studied by time-resolved laser spectroscopy at temperatures 10 K 5 T 5 -5 300 K. Besides of the emission bands peaking a t G = 17000 cm-l, 5 = 15750 cm-l, and 5 = = 13500 cm-l a fourth band peaking in the I R at i; = 10600 cm-l is registered. This I R band is closely connected to two excitation bands in the UV peaking at G = 26900 cm-l and 5 = 28750 cm-l (T = 10 K, x = 0.034). Four different Mn dominated centers are distinguished, which are partly connected by energy transfer. Die Lumineszenz-Anregungs-und Emissionsspektren von Znl -,Mn,S rnit hoher Mn-Konzentration (0,Ol 5 x 5 0,25) werden rnit zeitaufgeloster Laserspektroskopie im Temperaturbereich von T = 10 bis 300 K untersucht. AuBer den bekannten Emissionsbanden mit Maxima bei G = = 17000 cm-l, 5 = 15750 cm-l und 5 = 13500 cm-l wird eine vierte Emissionsbande mit einem Maximum bei Y" = 10600 cm-l beobachtet. Diese IR-Bande steht in enger Verbindung zu zwei Anregungsbanden im ultravioletten Spektralbereich mit Maxima bei G = 26900 cm-l und 28750 cm-l (T = 10 K ; x = 0,034). Vier unter Teilnahme von Mn gebildete Lumineszenzzentren werden unterschieden, die teilweise durch Energietransportprozesse miteinander verbunden sind.

Abstract— Photo‐alignment of anisotropic optical thin films enables realization of novel optical elements, which were not feasible up until now. Photo‐aligned anisotropic thin films can be applied to rigid or flexible substrates, which may be flat or curved. The optical performance of such films can be tailored to application‐specific requirements by introducing tilt profiles of the optical axis and/or generate patterned retarders with continuous or periodical in‐plane variation of the optical axis.