Application to Chemical Detection

The excitation of n-CdS at the band gap (Eg = 2.4 eV) produces a band edge photoluminescence spectrum with a A, ax near 510 nm, which is attributed to the radiative recombination of the photogenerated electrons 

These quantitatively reversible enhancements and quenching of the photoluminescence of n-CdS semiconductors by the addition of gaseous bases and acids, respectively, clearly indicate not only that such phenomena are associated w ith the intrinsic basicity or acidity of these gases but also that 

Quantitative analysis of the reduction in the depletion width has been obtained as follows  

Suib et at. (25, 254) reported the different effects of nickel and vanadium on the catalytic activity and selectivity for the fluid catalytic cracking by a photoluminescence technique and showed that the method is useful in predicting the catalyst deactivation caused by the deposition of metals on surfaces. The activity of the catalyst decreases monotonically with increasing vanadium content. With 1.5 wt% of V, the catalystad lost most of its activity, and with 2.0 wt% of V it became almost completely inactive. Such a deactivation of the catalyst was irreversible, with the extent being closely associated with the surface area covered with vanadium. Moreover, the extent of the deactivation was found to depend on the aging temperature, which was accelerated when aging was carried out under the same conditions normally sized in hydrothermal reactions. 

Quenching of the phololuminescence was found for the 2 wl% V-loaded catalyst, and in this system a new band appeared (25, 254). Vanadium-naphthenate and the vanadium-loaded catalyst exhibit similar photoluminescence spectra near 350 nm. Moreover, only the vanadium-loaded catalyst exhibits a broad emission at about 550 nm. After aging the vanadium- 

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