Synthesis of TOPO-capped Mn-doped ZnS and CdS quantum dots

TOPO (tri-n-octylphosphine oxide) capped Mn-doped ZnS and Mn-doped US nanop articles have been prepared from bis(diethyldithiocarbamato)zinc(ii) or bis (methylhexyldithiocarbamato)cadmium(ii) and manganese dichloride. The nanop articles obtained all show quantum-size effects in their optical spectra wi th respect to the parent US and ZnS. There are clear differences in the photoluminescence of the ZnS (448 nm) an d ZnS: Mn (510 nm) samples. The level of Mn-doping can be differentiated by the photoluminescence intensity, all of the doped samples show an emission maximum at 510 nm. EPR spectra and ICP results confirm the quantitative in corporation of manganese into the ZnS quantum dots. Selected area electron diffraction (SAED), X-ray diffraction (XRD) and transmission electron micro scopy (TEM) show the material to be hexagonal. The crystallinity of the mat erial was also evident from high resolution transmission electron microscop y (HRTEM) which gave well-defined images of particles with clear lattice fr inges. The PL spectrum of the doped US nanoparticles has an emission maximum at 58 5 nm as is usually attributed to the T-4(1)-(6)A(1) electronic transition o f manganese in a tetrahedral site. However the PL spectrum changes over tim e (weeks) to give a spectrum typical of the deep trap emission of CdS. SAED and XRD show both US and the Mn-doped US particles to be in the hexagonal phase. TEM and high resolution TEM show images of nanosize particles with c lear lattice fringes. EPR spectra and ICP results confirm the presence of m anganese in the US nanoparticles. EPR spectra showed that CdS: Mn was not s table over longer periods of time with segregation of manganese at the surf ace of particles in older samples of CdS. By contrast, the ZnS: Mn samples were quite stable for several weeks.