Transition metals, doped semiconductor nanocrystals

Several examples have been reported recently of solution-processed multilayer electroluminescence devices incorporating semiconductor nanocrystals as the active recombination centers (16-18, 164). Recently, attention has also turned to hybrid electroluminescent devices involving transition metal-doped nanocrystals (104, 165-167). Although many challenges remain, including more specific exploitation of the dopants in many cases, the devices demonstrated to date represent a new direction in application of doped semiconductor nanocrystals made possible by the compatibility of these luminescent nanocrystals with solution processing methodologies. 

The other interesting challenge from a synthetic viewpoint is the synthesis of doped QDs, particularly to study their magneto-optical properties. Doping transition metal ions in bulk as well as nanoscale semi-conductors has been an important area of study for the past couple of decades. Recent studies have further shown that for several applications, dopant associated emission from semiconductor nanocrystals may be more advantageous than the usual band-edge emission. Extensive attempts have been made to dope intentional impurities in various semiconductor nanocrystals, including those in ZnSe, ... 

Another fundamental phenomenon, which determines the behavior of conductivity in polymer-nanocomposites, is the percolation threshold, which occurs when the nanocrystals concentration reaches values high enough to provide conduction along the connected chains of nanoparticles. At the threshold values of filler concentration the conductivity of composite changes abruptly the absolute value of this change can reach 10 -10 Ohm/cm, which makes this effect similar to the metal-insulator transition in doped compensated semiconductors (Mott transition). 

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