Figure 1: Energy transfer mechanism.

(a) Schematic illustration of proposed energy transfer mechanism in the emitter dopant:assistant dopant:host matrix under electrical excitation and chemical structures of the assistant dopants used in this study. (b–e) Fluorescence spectra of assistant dopant:host co-deposited film (upper), and absorption (dashed line) and fluorescence (solid line) spectra of emitter dopant in solution (10⁻⁵ mol l⁻¹ in CH₂Cl₂) (bottom). Rather large Förster transfer radii of ~2.2, ~7.3, ~6.9 and ~10 nm were estimated for blue, green, yellow and red EML matrices based on the spectral overlap between the absorption spectrum of the acceptor and the PL spectrum of the donor, suggesting that efficient FRET is possible.