| abstract |
A new means for tuning the emission spectrum of OLEDs (100), while retaining a high luminescence efficiency is disclosed wherein the emission spectrum of a polar luminescent molecule is wavelength shifted by as much as 70 nm when doped into a conductive host in a vacuum-deposited molecular organic light emitting device (100). The effect may be attributed to changes in the average dipole moment of the host thin film that are induced by the addition of highly dipolar dopant molecules. This phenomenon may be referred to as a 'solid state solvation effect' in analogy to similar effects previously identified in solution chemistry. In experiments using singly doped devices, different concentrations of a polar laser dye known as DCM2 are doped in non-polar triarly amine conductive host films. In these experiments, DCM2 performs the dual role of functioning both as the luminescent center and as the source of the increased spatially averaged dipole moment. In a second set of experiments using dual-doped devices, DCM2 is employed only as the luminescent center in a non-polar host, while a second polar dopant, aluminum tris(8-hydroxyquinoline) (Alq3), is introduced to generate the local dipole moment. By changing the concentration of Alq3, while keeping the DCM2 concentration fixed the OLED emission may be tuned over a range of 30 nm. For the singly doped devices, the external luminescence quantum efficiency, n, decreases with dopant concentration due to aggregation induced quenching. However, for the dual-doped devices, n increases with an increase in the bathochromic shift. |