Organic light-emitting diodes (OLEDs) based on small-molecule materials are currently developed for applications
in flat panel displays and general lighting sources. However, a large number of efficient deep blue emitters
still suffer from rather fast degradation and thus, requires further improvement.
The aim of the present work is to gain a fundamental understanding of the intrinsic degradation processes causing
the low stability of blue OLED emitters. For this purpose we study the photoluminescence (PL) degradation
instead of the most often investigated electroluminescence (EL) degradation to separate electrically and optically
generated effects.
We show a newly developed PL lifetime measurement system which allows the study of degradation processes
under the influence of either electron or hole currents. Using this set-up we demonstrate the very high PL stability
of the highly efficient blue singlet emitter 2,2',7,7'-tetrakis(2,2-diphenylvinyl)spiro-9,9'-bifluorene (Spiro-
DPVBi) under electron and hole currents and compare this to the lifetime of OLEDs using the same emitter material.
We present a concept for representing uncertain topological relations and their derivation from uncertain sets, useful for spatial and temporal reasoning in GIS. The concept is based on the notion of a stochastic boundary of a geometric set and on tests performed to decide the validity of relations between the sets. It uses the power-function to derive the probabilities of the found relations. The concept is applicable to all questions where uncertain geometric queries or analysis have to be performed.
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