Effects of dipole orientation and birefringence on the optical emission from thin films

Polymers are frequently used as the emissive material in optical devices su ch as the light emitting diode. The long chain molecular structure of typic al polymer materials together with the spin coating technique by which thin layers are fabricated results in significant optical birefringence. We out line a classical model for spontaneous emission from within such birefringe nt materials in planar multi-layer structures. We compare the results obtai ned using this model with experimental data on the radiation pattern produc ed by a thin film of the conjugated polymer poly[2-methoxy, 5-(2'-ethyl-hex yloxy) 1,4 phenylenevinylene] (MEH-PPV). As a control we also measured the radiation pattern from the dye Lumogen, dispersed as a guest in an opticall y isotropic thin film of polycarbonate. We find that birefringence and the orientation of the dipole moment of the polymer have to be taken into accou nt to understand the departure from the expected Lambertian radiation patte rn that we observe from MEH-PPV. (C) 2000 Elsevier Science B.V. All rights reserved.