Temperature samples quenched from oxygen

Oxygen Nonstoichiometry. Samples quenched from oxygen at 750C and air at 950C have been studied. A value near 6.5 for the oxygen stoichiometry is expected for both of these samples (10). The samples are found to be semiconducting by measurement of their resistance vs temperatures curves. The reflectance spectrum of the air quenched sample has been taken to directly determine the value of the optical band gap in these materials. The reflectance spectrum in the infrared is presented in Figure 1. As in... 

The phosphorescence lifetimes have been examined for many protein systems as a function of temperature. In the early work oxygen was not removed from the sample.(72,73) In these works the lifetimes are dominated by quenching by oxygen, and so the temperature dependencies probably represent temperature-dependent oxygen diffusion. 

Several other diaryl and alkylarylketones also exhibit room temperature phosphorescence in air equilibrated samples when included in silicalite [83c] or forming inclusion complexes with cyclodextrins [83c, 102], depending on the probe and cavity size. Both substrates provide some degree of protection from oxygen quenching, as well as imposed conformational restrictions that decrease the non-radiative mechanisms of deactivation. 

The frozen in photoconductivity, as was concluded by Melnick, will arise from effects of the surface barrier layer or, of course, would arise similarly from any other rate-limiting process in the adsorption of oxygen. For our model in this discussion we shall use electron transfer over the surface barrier as the rate-limiting reaction. In this case, the rate at which adsorption occurs is proportional to exp ( —Ei/kT), where E2 is the barrier height. Thus if we measure the decay in photoconductivity (the chemisorption of oxygen) at room temperature, and then suddenly quench the sample to 130°K, it is obvious that the rate of decay in photoconductivity will decrease considerably. The change in the rate will be dependent on Ei and the temperature to which the sample is quenched. 

---