When preparing CdSe nanoparticles in polybutadiene-based polymer matrices, quantum confinement in the smaller particles leads to the usual increase in the band-gap energy, with associated, well defined, band-edge luminescence emission. However, for samples whose size was smaller than 3nm, new broad luminescence features appear, with the simultaneous appearance of a new paramagnetic defect center that had not previously been reported in the literature. This work concentrates on analyzing the electron paramagnetic resonance of the new defect, which was found to be located at a trigonally-distorted tetrahedral site, with a spin S = 1/2 and g-values g|| = 2.321 and g = 2.053. With the attribution of very poorly resolved hyperfine interaction to a nucleus of spin I = 3/2, the identity of the defect was ascribed to Cu in its d9 state, which would be expected to act as a simple acceptor center in CdSe. Conclusions were drawn to the effect that the defect normally resides within the valence band for bulk and large particles, only becoming apparent as a defect within the band-gap as the energy increased above 2.6eV in the smaller particles.

Appearance of Copper d9 Defect Centres in Wide-Gap CdSe Nanoparticles - a High-Frequency EPR Study. N.R.J.Poolton, G.M.Smith, P.C.Riedi, J.W.Allen, A.V.Firth, D.J.Cole-Hamilton, E.J.L.McInnes: Physica Status Solidi B, 2005, 242[4], 829-35