Exciton luminescence of ZnO fine particles

Revealing hole trapping in zinc oxide nanoparticles by time-resolved X-ray spectroscopy

Nanostructures of transition metal oxides, such as zinc oxide, have attracted considerable interest for solar-energy conversion and photocatalysis. Both applications are sensitive to the transport and trapping of photoexcited charge carriers. The probing of electron trapping has recently become possible using time-resolved element-sensitive methods, such as X-ray spectroscopy. However, valence-band-trapped holes have so far escaped observation. Herein we use X-ray absorption spectroscopy combined with a dispersive X-ray emission spectrometer to probe the charge carrier relaxation and trapping processes in zinc oxide nanoparticles after above band-gap photoexcitation. Our results, supported by simulations, demonstrate that within 80 ps, photoexcited holes are trapped at singly charged oxygen vacancies, which causes an outward displacement by ~15% of the four surrounding zinc atoms away from the doubly charged vacancy. This identification of the hole traps provides insight for future developments of transition metal oxide-based nanodevices.

Metal-oxide nanostructures are used in a range of light-driven applications, yet the fundamentals behind their properties are poorly understood. Here the authors probe photoexcited zinc oxide nanoparticles using time-resolved X-ray spectroscopy, identifying photocatalytically-active hole traps as oxygen vacancies in the lattice.

Optoelectronic characteristics of YAG phosphor-incorporated ZnO films deposited by ultrasonic spray pyrolysis

This work presents a novel white light device. An yttrium aluminum garnet (YAG) phosphor-incorporated zinc oxide (ZnO) film is deposited on a slide glass substrate by ultrasonic spray pyrolysis. A nanoflower consisting of a hexagonal nanopetal is formed on the surfaces of the samples, and the sizes of the nanopetal are approximately 200 to 700 nm. Additionally, the nanopetal becomes blunted with an increasing incorporated amount of YAG. As the incorporated amount is 1.5 and 2.5 wt.%, the photoluminescence color of the YAG-incorporated ZnO film is nearly white, possibly contributing to the YAG emission and the band-to-deep level transition in the ZnO film.