Hole phosphorescence devices

Tsai et al. (2) determined that blue phosphorescent organic light-emitting devices consisting of 2,2 -bis(A,A-disubstituted amino)-9,9 -spirobifluorenes, (I), were effective as hole transporting materials and had efficiencies of up to 16%, 30.6 cd/A and 26.7 lm/W. 

The Phosphoroscope. This is a simple mechanical device which allows the separation of long-lived emissions (phosphorescence) from short-lived emissions which consist of scattered light and fluorescence. It is a disc or drum in which there are holes or slots placed in such a way that the excitation and emission beams reach the sample and the detector respectively at different times. With the fastest practicable rotation velocities of the phosphoroscope, the cut-off time is of the order of 1 ms. 

Some of these carriers may recombine within the emissive layer yielding excited electron-hole pairs, termed excitons. These excitons may be produced in either the singlet or triplet states and may radiatively decay to the ground state by phosphorescence (PL) or fluorescence (FL) pathways (Fig. 1-2). An important figure of merit for electroluminescent materials is the number of photons emitted per electron injected and this is termed the internal quantum efficiency. It is clear, therefore, that the statistical maximum internal efficiency for an EL device is 25% as only one quarter of the excitons are produced in the singlet state. In practice, this maximum value is diminished further because not all of the light generated is visi-... 

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