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Notes: Preservation of products with the combination of 5-chloro-2-methyl-4-isothiazolinone (methylchloroisothiazolinone, MCI) and 2-methyl-4-isothiazolinone (methylisothiazolinone, MI), commercialized as Kathon CG or WT, is widely used. Allergic contact dermatitis reactions to the preservative have been described in many publications of epidemiological studies. In addition, a number of allergic, airborne reactions to MCI/MI were observed in recent years. The aim of the presented study was: (i) to compare epidemiological data of MCI/MI with data of other preservatives; (ii) to estimate the possible exposure to MCI/MI from commercial products and the distribution of MCI/MI in chemical products based on a product evaluation of the chemical product register of the Swiss Federal Office of Public Health; (iii) to estimate the exposure to MCI/MI, volatile organic chemicals (VOC) and glycols from freshly painted walls; (iv) to compare the contact allergenic potential of MCI/MI with other preservatives. It was found that the number of registered chemical products, unambiguously identifiable as containing MCI increased from 3644 products in July 1999 to 4843 products in April 2001 in Switzerland. It is estimated that today, the total number of chemical products preserved with MCI/MI on the Swiss market is about 6000. A further increase is to be expected. The contact allergenic potential of MCI/MI seems to be higher than for other preservatives. Measurements of MCI/MI concentrations in air samples of freshly painted rooms have shown that the concentration of MCI/MI in the air a few days after painting may be high enough to elicit airborne reactions in already-sensitized patients. In a single case, reactions to MCI/MI were observed over months after wall painting. In this case, both wall paint and plaster contained MCI (40 and 46 ppm). Volatile organic chemicals (VOC) may also be relevant for the elicitation of airborne reactions. In 1/3 of the measurements, the VOC concentrations measured within 14 days after painting were in a range within which sensory irritation and discomfort may be induced. Declaration of MCI/MI-containing products, replacement of MCI/MI by alternative preservatives or the separate use of preservatives in industrial products and in cosmetics might reduce the risk of airborne reactions.

Notes: The trap-related photoluminescence dynamics in CdSxSe1−x nanocrystals (for x=0.24 and x=0.74) in glass were studied in the temperature interval 10–300 K. A close link between the temperature behavior of the photoluminescence decay rate and that of the photoluminescence efficiency was found, which indicates a dominant role of nonradiative recombination. The trap-related photoluminescence was interpreted as the recombination of a shallowly trapped electron with a hole in a deep trap. An exponential decrease (with a constant in the range 0.2–0.4 eV) in the density of the deep traps with increasing energy above the valence band was found. Apart from the Arrhenius type of temperature behavior of decay rate with the activation energy (approximate)50 meV, the Berthelot type (characteristic temperature (approximate)160 K) was also observed. The latter was modeled by carrier tunneling between localized sites and the energetic distribution of the tunneling distances was obtained. © 2000 American Institute of Physics.

Notes: We report on picosecond dynamics of photoexcited carriers in CsPbCl3 nanocrystals in a CsCl host. For low carrier densities, photoexcited carriers form excitons, which decay with a characteristic time constant of 170 ps at 300 K. Under strong photoexcitation, we have observed the Auger recombination with the Auger coefficient C(approximate)10−29 cm6 s−1. We have identified the onset of the Auger recombination at the carrier densities of (approximate)1020 cm−3 as the Mott-like transition from excitons to electron–hole plasma in nanocrystals. © 2000 American Institute of Physics.

Notes: We report on the picosecond laser induced grating technique applied to hydrogenated microcrystalline silicon (μc-Si:H) and aimed at studying the photocarrier diffusion coefficient D. We have studied a series of three samples having a distinctly different content of the crystalline phase, and the microstructure and morphology of which are known in detail. Our results show that the coefficient D scales with the degree of crystallinity of the samples, reaching values up to D=9 cm2 s−1 close to crystalline silicon. The obtained carrier lifetime ((approximate)1 ns) is constant in all measured samples. The extracted diffusion lengths are much greater than the dimensions of the microcrystalline grains in the samples. We conclude that small grain boundaries do not limit substantially the carrier diffusion length in microcrystalline silicon. © 2001 American Institute of Physics.

Notes: We report on ultrafast carrier dynamics in nanocrystalline CdSe thin films prepared by chemical solution deposition. The photoluminescence and transient absorption dynamics have spectrally dependent decay faster at shorter wavelengths. The spectral behavior of the decay rates in samples with different nanocrystal sizes and the sensitivity of the dynamics on the surface modification indicate the dominant role of the surface states in the photoluminescence. © 2000 American Institute of Physics.