  Present work focuses on the effective doping of multi-walled carbon nanotube
(CNT) in the ZnS:Cu phosphor system and thereafter improvement in the optical
performance of electroluminescent (EL) device due to the effect of increased
local field. To facilitate doping of CNTs into the phosphor and decrease the
operating voltage of the EL device, CNTs were shortened by milling and
incorporated effectively using a flux assisted solid-state annealing reaction.
Interestingly shorter the length of CNTs used, greater was the local field
enhancement, brightness and efficiency observed for the EL devices. When the
field is applied, adequate charge carriers are tunneled into the ZnS:Cu system
through the tips of the CNTs by forming high energy hot spots thus enhancing
the local field. The improved device characteristics are due to field
enhancement without flowing of undesired current in the EL device and effective
transfer of energy from hot spots to copper activator causing field-ionization.
The detailed electrical characterization of the novel EL device along with its
brightness measurements are also presented by considering the hot electron
injection model.
