Three-colour single-mode electroluminescence from Alq₃ tuned by microcavities

Organic metal microcavities were fabricated by using full-reflectivity aluminium film and semi-transparent silver film as cavity mirrors. Unlike conventional organic microcavities, such as the typical structure of glass/DBR/ITO/organic layers/metal mirror, a microcavity with a shorter cavity length was obtained by using two metal mirrors, where DBR is the distributed Bragg reflector consisting of alternate quarter-wave layers of high and low refractive index materials. It is realized that red, green and blue single-mode electroluminescence (EL) from the microcavities with the structure, glass/Ag/TPD/Alq₃/Al, are electrically-driven when the thickness of the Alq₃ layer changes. Compared to a non-cavity reference sample whose EL spectrum peak is located at 520 nm with a full width at half maximum (FWHM) of 93 nm, the microcavity devices show apparent cavity effects. The EL spectra of red, green and blue microcavities are peaked at 604 nm, 540 nm and 491 nm, with FWHM of 43 nm, 38 nm and 47 nm, respectively.