Solid state cathodoluminescence based on tris-(8-hydroxyquinoline) aluminum and its quenching mechanism

A novel solid state cathodoluminescence (SSCL) device (the device has a structure of ITO/SiO2/Alq(3)/SiO2/Al) is fabricated using organic materials as the fluorescent film sandwiched between two SiO2 layers. When alternating current (AC) voltage is applied to this device, uniform emissions are observed. When the voltage is 50 V, a longer wavelength emission (522 nm) is obtained, but the shorter wavelength emission (465 nm) is dominant when the voltage is 76 V. The origins of these emissions are discussed. The interface formed between SiO2 and tris-(8-hydroquinoline) aluminum (Alq(3)) of SSCL device was investigated by using X-ray photoelectron spectroscopy (XPS). Analyses of the XPS spectra reveal a deep diffusion of the indium into the interface. On the other hand, the interaction between indium and Alq3 occurs at the interface and results in the formation of a carbon-oxygen-metal (In or Al) complex in the contact region. This effect causes a luminescence quenching in the SSCL device.