Gold nanocubes demonstrate unique optical properties of the high photoluminescence (PL) quantum yield and a remarkably enhanced extinction band at 544 nm. The 4 x 10(-2) PL yield, which is about 200 times higher than that of gold nanorods, allows gold nanocubes to be successfully used in cell imaging of human liver cancer cells (QGY) and human embryo kidney cells (293T) with a common method of single-photon excitation. The high extinction coefficients of gold nanocubes also facilitate them carrying out the photothermal therapy of QGY and 293T cells, showing similar photokilling efficiency as compared to gold nanorods.

Time-dependent photoluminescence (PL) enhancement, blue shift, and photobleach were observed from the thiol-capped CdTe quantum dots (QDs) ingested in mouse myoblast cells and human primary liver cancer cells. It was revealed that the PL blue shift resulted from the photooxidation of the QD core by singlet oxygen molecules formed on the QD core surface.

The process and mechanism of photochemical instability of thiol-capped CdTe quantum dots (QDs) in aqueous solution were experimentally studied. After laser irradiation, the corresponding Raman bands of the Cd-S bond decreased obviously, indicating bond breaking and thiol detachment from the QD surfaces. Meanwhile, a photoinduced aggregation of QDs occurred with the hydrodynamic diameter increased to hundreds of nanometers from an initial 20 nm, as detected with dynamic light scattering measurements. The bleaching of the photoluminescence of QDs under laser irradiation could be attributed to the enhanced nonradiative transfer in excited QDs caused by increased surface defects due to the losing of thiol ligands. Singlet oxygen (1O2) was involved in the photooxidation of QDs, as revealed by the inhibiting effects of 1O2 quenchers of histidine or sodium azide (NaN3) on the photobleaching of QDs. The linear relationship in Stern-Volmer measurements between the terminal product and the concentration of NaN3 demonstrated that 1O2 was the main pathway of the photobleaching in QD solutions. By comparing the photostability of QDs in C2C12 cells with and without NaN3 treatment, the photooxidation effect of 1O2 on photobleaching of cellular QDs was confirmed.

The energy band structures and density of states for N-doped and N:H-doped anatase TiO 2 are calculated based on the first-principles density-functional theory. For N-doped TiO 2 , there appear two isolated states above the top of the valence band and the band gap narrowing is very small. With the same nitrogen dopant concentration, N:H doping yields a significant band gap narrowing. The calculated results support our experimental data that N:H-doped TiO 2 exhibited higher visible-light photocatalytic efficiency than the N-doped one.

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