Soo-Keun Lee

A web-based overview of semiconductor photochemistry-based current commercial applications

The major current commercial applications of semiconductor photochemistry promoted on the world wide web are reviewed. The basic principles behind the different applications are discussed, including the use of semiconductor photochemistry to: photo-mineralise organics, photo-sterilise and photo-demist. The range of companies, and their products, which utilise semiconductor photochemistry are examined and typical examples listed. An analysis of the geographical distribution of current commercial activity in this area is made. The results indicate that commercial activity in this area is growing world-wide, but is especially strong in Japan. The number and geographical distribution of patents in semiconductor photocatalysis are also commented on. The trends in the numbers of US and Japanese patents over the last 6 years are discussed.

Photodecomposition of ozone sensitised by a film of titanium dioxide on glass

High levels of ozone (typically 850 ppm) are readily decomposed by semiconductor photocatalysis, using a thin film of the semiconductor titanium dioxide (Degussa P25 TiO2) cast on a glass tube, and UVA light, i.e. light of energy greater than that of the bandgap of the semiconductor (ultra-bandgap light); in the absence of this light the thermal decomposition of ozone is relatively slow. The semiconductor films show no evidence of chemical or photochemical wear with repeated use. At high levels of ozone, i.e. 100 ppm less than or equal to [O-3] less than or equal to 1400 ppm, the initial rate of ozone decomposition by semiconductor photocatalysis is independent of [O-3], whereas, at lower ozone concentrations, i.e. 5 ppm less than or equal to [O-3] less than or equal to 100 ppm, the initial rate of ozone photodestruction decreases in a smooth, but non-linear, manner with decreasing [O-3]. The kinetics of ozone photodecomposition fit a Langmuir-Hinshelwood type kinetic equation and the possible mechanistic implications of these results are briefly discussed.

Mechanically driven light-generator with high durability

Mechanically activated luminescence from solids (mechanoluminescence) is a classical optical phenomenon induced in a substance when stressed or cleaved. However, no practical application has been realized due to its low luminescent intensity and lack of reproducibility. We demonstrate highly bright and durable mechanoluminescent flexible composite films with a brightness of ∼120u2009cd/m2 and durability over ∼100 000 repeated mechanical stresses by using a combination of copper-doped zinc sulfide (ZnS:Cu) particles and polydimethylsiloxane. Furthermore, the possibility of mechanoluminescent color-tuning by changing the repetitive stress rate on the composite films is also suggested. These findings can open a window for developing smart systems and opto-mechanical devices.

Self-cleaning titania films: an overview of direct, lateral and remote photo-oxidation processes

An overview of the recent investigations into the direct, lateral and remote oxidation of carbon-containing materials is given. The overview begins with the pioneering work of Fujishima and his co-workers involving the remote bleaching of methylene blue by UV-irradiation of titania in the gas phase. The further research of these workers conducted on the remote photocatalytic destruction of various polymers and dyes is then discussed briefly. The notable work of Paz and his co-workers on the lateral, but not remote, oxidation of octadecyltrichlorosilane (OTS) by photoeteched titania films is then examined. The striking observations associated with the lateral oxidation of soot by UVirradiated thin titania films, reported by Choi and his colleagues, are reported. Finally, the results of our most recent work on soot covered titania films in which the direct, lateral and remote oxidation of soot by UV-irradiated thick titania films could be observed visually is discussed. The most likely agent responsible for these photocatalytic oxidation processes is considered and a suitable candidate, hydroxyl radicals, suggested.

The alteration of the structural properties and photocatalytic activity of TiO2 following exposure to non-linear irradiation sources

When TiO2 powder was irradiated with a laser light (>0.8 MW peak pulse power (PPP) at 355 nm) a visible change in its colour from white to dark blue was observed. The initial rate of change of the total colour difference was related to the laser light intensity and the longer the irradiation time the more substantial the colour change. The result of X-ray diffraction (XRD) studies showed that the crystal structure of the TiO2 developed a more rutile form after laser exposure. ESR studies indicated that the colour change was associated with the generation of Ti(III) species in the photocatalyst. Electron microscopic studies showed that more spherical shaped particles of TiO2 were observed after laser treatment although the average particle size remained largely unchanged. No significant changes in the band gap or the surface area of the laser modified TiO2 were observed. The laser modified photocatalyst showed no enhancement in activity for the destruction of methylene blue, rhodamine B and stearic acids, indicating that the rutile/anatase ratio is unimportant in the destruction of the test pollutants used in this work, via TiO2 photocatalysis.

Diagnostic of laser contrast using target reflectivity

Using three different laser systems, we demonstrate a convenient and simple plasma based diagnostic of the contrast of high-power short-pulse lasers. The technique is based on measuring the specular reflectivity from a solid target. The reflectivity remains high even at relativistic intensities above 10(19) W/cm(2) in the case of a high-contrast prepulse-free laser. On the contrary, the specular reflectivity drops with increasing intensities in the case of systems with insufficient contrast due to beam breakup and increased absorption caused by preplasma.

Luminescence of Leuco-Thiazine Dyes

Details of the novel luminescence of the leuco forms of the thiazine dyes, methylene blue and thionine, are reported, including their emission maxima, quantum yields and lifetimes of the luminescence. Other work shows that this luminescence is independent of reducing agent type and solution pH and is a common feature of most thiazine dyes.

On‐Target Contrast Diagnostic via Specular Reflectivity Measurement

High‐power laser contrast is challenging to measure, especially in the real target irradiation conditions. We present a convenient and relatively simple contrast diagnostic technique based on the measurement of target specular reflectivity at full laser power. The reflectivity remains high even at intensities above 1019u2009W/cm2 in the case of a high‐contrast prepulse‐free laser. On the contrary, the specular reflectivity drops in the case of lower contrast, due to the beam break‐up and increased absorption caused by the preformed plasma. The technique was demonstrated using three different laser systems with several contrast conditions: Astra (CLF, RAL), TiS laser at APRI, GIST, and J‐KAREN (APRC, JAEA).