The tuning of CdSe quantum dot (QDs) sizes, and consequently their corresponding two-photon absorption (TPA) cross section, has been systematically investigated. As the size (diameter) of the quantum dots increases, the TPA cross section is found to be empirically related via a power-law proportionality of 3.5+/-0.5 and 5.6+/-0.7 to the diameters of CdSe and CdTe QDs, respectively. The results are tentatively rationalized via a theoretical model of two-photon excitation properties in a system incorporating excitons and defects.

The synchronous existence of two different tumors in the gastrointestinal tract is uncommon. We report the case of a 75-year-old man who had a concurrent gastrointestinal stromal tumor and adenocarcinoma at the gastroesophageal junction. The two tumors arose at the same site but had distinct morphologies. The etiology of synchronous tumors is still unclear and their coexistence causes problems for the surgeon, oncologist and pathologist in terms of their diagnosis, treatment, and follow-up. We report a rare case of synchronous tumors and a review of the literature.

Using synchrotron powder X-ray diffraction (PXRD) and small-angle X-ray scattering (SAXS), we have studied the structures of the two CdSe/CdTe and CdTe/CdSe type II quantum dots (QDs), including the crystalline structure, particle shape and size, as well as phase separation of the two components. The X-ray results suggest that the spherical CdTe/CdSe QDs of the size ∼8 nm, synthesized in a two-step procedure with CdTe nanoparticles (4 nm) as nuclides, have the structure of a CdTe-rich core enclosed by a CdSe shell. On the other hand, the spherical CdSe/CdTe QDs of the size ∼9 nm, synthesized via a similar two-step procedure but with CdSe nanoparticles (∼3 nm) as nuclides, show mainly one-phase structure with a relatively uniform distribution of CdSe and CdTe. The phase separation of the two components CdSe and CdTe inside each of the two QDs, a decisive factor in the photovoltaic applications, is furthermore examined using anomalous SAXS (ASAXS) for a consistent conclusion. For comparison, single-phase nanoparticles CdSe and CdTe are also examined. The correlation between the synthesis procedures and the corresponding structures of the QDs is discussed.

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