The enhancement on the plasma illumination characteristics of inverted pyramidal cavity (IPC) devices due to the utilization of diamond films as cathodes was illustrated. The performance of the plasma illumination characteristics of the IPC devices was closely related to the electron field emission (EFE) properties of the cathode materials. The duplex-structured microcrystalline/ultrananocrystalline (MCD/UNCD) diamond films, which possessed lower turn-on field for inducing the EFE process (E-0= 10.9 V/mu m), resulted in the better plasma illumination performance for the IPC devices. The plasma can be triggered at the lower threshold field of E-th= 2300 V/mm. Transmission electron microscopic studies revealed that the MCD/UNCD films contain nano-graphite clusters, which facilitated the transport of electrons and were presumed to be the prime factor, resulting in superior EFE properties for the MCD/UNCD films and the better plasma illumination characteristics for the IPC devices. (C) 2012 Elsevier B. V. All rights reserved.