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This study examined the optical and electronic properties of post-annealed Al-doped ZnO ͑ZnO:Al͒ thin films. The lowest resistivity was observed after annealing a sputter-deposited ZnO:Al film at 350°C. X-ray photoelectron spectroscopy revealed a ϳ0.4 eV shift in the Fermi level when the carrier concentration was increased to 1.6ϫ 10 20 cm −3 by Al doping and annealing. The optical band gap increased from 3.2 eV for insulating ZnO to 3.4 eV for conducting ZnO:Al, and was associated with conduction-band filling up to ϳ0.4 eV in a renormalized band gap. Schematic band diagrams are shown for the ZnO and ZnO:Al films.

The photoluminescence behavior of CdS quantum dots in initial growth stage was studied in connection with an annealing process. Compared to the as-synthesized CdS quantum dots (quantum efficiency ≅ 1%), the heat-treated sample showed enhanced luminescence properties (quantum efficiency ≅ 29%) with a narrow band-edge emission. The simple annealing process diminished the accumulated defect states within the nanoparticles and thereby reduced the nonradiative recombination, which was confirmed by diffraction, absorption, and time-resolved photoluminescence. Consequently, the highly luminescent and defect-free nanoparticles were obtained by a facile and straightforward process.

Gold nanoparticles of $100 nm in diameter were incorporated into TiO 2 nanoparticles for dye-sensitized solar cells (DSSCs). At the optimum Au/TiO 2 mass ratio of 0.05, the power-conversion efficiency of the DSSC improved to 3.3% from a value of 2.7% without Au, and this improvement was mainly attributed to the photocurrent density. The Au nanoparticles embedded in the nanoparticulate-TiO 2 film strongly absorbed light due to the localized surface-plasmon resonance, and thereby promoted light absorption of the dye. In the DSSCs, the 100 nm-diameter Au nanoparticles generate field enhancement by surface-plasmon resonance rather than prolonged optical paths by light scattering. V

Mn-doped zinc sulfide nanoparticles were synthesized using a liquid-solid-solution method, as a simple synthetic route for preparing nearly monodispersed nanocrystals with a diameter of 7.3±0.7nm. The influence of doping concentration for optimum luminescence properties was studied with the nonuniform distribution of local strain and the capping effect. The improved photoluminescence properties of the 450°C-annealed samples with 1.0at.% Mn doping are attributed to both the removal of water/organics and the enhanced crystallinity (reduced local strain).

Precise control of photoluminescence enhancement and quenching of semiconductor quantum dots using localized surface plasmons in metal nanoparticles

The effects of hydroxyl quenching were examined on the photoluminescence properties of SnO 2 :Eu 3+ nanoparticles. High-quality SnO 2 :Eu 3+ nanoparticles were simply synthesized from SnCl 4 , EuCl 3 , and ethylene glycol. The photoluminescence spectra showed a reddish orange emission, which gradually increased with the calcination temperature in the range from 700 to 1000 °C. As the calcination temperature varied, the change of the OH -/O 2integrated-intensity ratios from X-ray photoelectron spectroscopy (XPS) was qualitatively consistent with that of the photoluminescence intensities. The samples obtained after the hydrothermal treatment and after reheating, respectively, exhibited a decline and recovery of their emission intensities, and this behavior with XPS confirmed the hydroxyl-quenching effect.

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