The influence of Nd3+ ions was investigated on the precipitation and optical properties of PbS quantum dots (QDs) inside silicate glasses. The diameters of the PbS QDs decreased as the concentration of Nd3+ in the glass increased as evidenced by blue shifts in the absorption and photoluminescence spectra. Electron energy loss spectroscopy shows that Nd3+ ions exist preferentially inside the PbS nanocrystals rather than in the glass matrix. We postulate that Nd–O clusters are preserved during heat treatment and serve as nucleation sites for PbS crystals. No change in the local bonding scheme of the Nd3+ ions was observed following heat treatment.

The influence of Nd 2 O 3 addition on the precipitation kinetics of lead chalcogenide (PbS) quantum dots (QDs) in silicate glasses was investigated. Energy dispersive X-ray spectroscopy (EDS) indicated that the Nd 3+ ions are preferentially located inside the PbS QDs rather than in the glass matrix. Changes in diameter (D) of PbS QDs exhibited smaller time dependencies (i.e., D%t 0.270-0.286 ) than that predicted by the classical Lifshitz-Slyozov-Wagner (LSW) theory. This is due to the limited concentrations of Pb 2+ and S 2À ions and the large diffusion distance inside the glass matrix. In addition, extended X-ray absorption fine structure (EXAFS) results indicated that the formation of PbS QDs was retarded due to the presence of Nd 2 O 3 in the glasses, as the large NdO x polyhedra interrupt the diffusion of Pb 2+ and S 2À ions. We believe that these Nd 3+ ions are primarily located in PbS QDs in the form of Nd-O clusters, and that the PbS QDs are built on top of these clusters. K E Y W O R D Sglass, optical materials/properties, rare earths

The first 3-D direct observation of clusters of Nd oxide inside silicate glasses was achieved using atom probe tomography. Three-dimensional elemental maps of major chemical elements in glasses such as Si, Al, Zn and O showed no evidence of regions that had concentrations higher than the average values, whereas the Nd aggregated into regions of high concentration. Elemental maps of Nd and Pb recorded from the glasses containing PbS QDs showed highly-concentrated areas of both elements at the same locations; this result indicates that PbS QDs formation started in association with the Nd clusters.

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