Significant enhancement of UV luminescence (∼2 orders of magnitude) with good stability has been achieved in solution-grown ZnO nanorods by hydrogen doping, which has been investigated by PL and Raman analysis, and, especially, by directly probing with solid state NMR.

Bright and stable structured green luminescence (GL) is achieved from solution-grown Cu-doped ZnO nanorods. Dependence of photoluminescence on the annealing parameters reveals that GL is correlated with creation of Zn vacancies (V_Zn) and then formation of Cu dopants at Zn sites (Cu_Zn). High internal quantum efficiency (43%) of the GL can be sustained up to 240 K due to negative thermal quenching. In contrast to the poor stability of defects-related visible emission, the structured GL shows good stability with respect to sample heating. Cu-doped ZnO nanorods with strong and stable GL have potential applications in visible light display and lighting.

Poor near-band-edge emission (NBE) prohibits the application of solution-grown ZnO nanorods in optoelectronics, thus their photoluminescence (PL) was studied with respect to post-annealing temperature and duration. A universal behavior was revealed: NBE was enhanced by one order (or two) of magnitude after annealing in air (or H₂) at about 425 °C for 30 min, while the enhancement factor starts to decrease after annealing at higher temperatures. The evolution of PL was mainly ascribed to annealing-induced activation and dissociation of hydrogen donor, which was identified as H_O by both PL and Raman analyses. Results from nanorods with different diameters and annealing gases further support this assignment. The results provide new insights to understand and optimize the properties of solution-grown ZnO.

It is now accepted that the physical forces in ultrasonic cleaning are due to strongly pulsating bubbles driven by the sound field. Here we have a detailed look at bubble induced cleaning flow by analyzing the transport of an individual particle near an expanding and collapsing bubble. The induced particulate transport is compared with a force balance model. We find two important properties of the flow which explain why bubbles are effectively cleaning: During bubble expansion a strong shear layer loosens the particle from the surface through particle spinning and secondly an unsteady boundary layer generates an attractive force, thus collecting the contamination in the bubble's close proximity.