Solvent complexes with the amino acid tryptophan have been studied spectroscopically in the S0-S! origin region by using supersonic free jet techniques. The major spectroscopic method employed was laser-induced fluorescence excitation spectra; individual features were also characterized by use of fluorescence lifetime determinations or dispersed emission spectra. Addition of proton-donating solvents results in the appearance of a slightly blue-shifted band in the vicinity of 34 960 cm"1 11. Evidence suggests that this band results from interactions analogous to those that produce a similar band upon proton solvent addition to tryptamine. Unlike the case of tryptamine, other site addition possibilities in tryptophan bring about slightly red-shifted solvent bands as well.

Laser-induced fluorescence spectroscopy was used to investigate β-phenylethylamine molecules that were cooled via supersonic gas expansions. The bare molecule spectra reveal 0-0 transitions that can be attributed to four separate conformers. Upon the addition of water or alcohol solvents, a series of new peaks is induced that appear to be built off separate bare molecule transitions. This is a pattern that is markedly different from the one seen for solvent addition to tyramine, which includes an-OH in the para position. As a result, definite hypotheses can be made to explain the influence of the para-OH in affecting solvent induced conformations.

Using fluorescence-based techniques (excitation and emission spectra lifetimes), we have studied the jet-cooled tyrosine derivatives tyramine and 3-(4-hydroxyphenyl) propionic acid (HPA). For solvent addition resulting in small, mainly one adduct complexes, there is a high degree of analogy with the results for the corresponding analogs of the amino acid tryptophan. In particular, for tyramine, as had been the case with its tryptophan analog tryptamine, addition of one -OH bearing solvent molecule at the α-amine apparently results in a complex in a single conformation.

The defects responsible for the short-wave (720 nm) and medium-wave (820 nm) luminescence in cuprous oxide can be created by annealing the crystal at a temperature of 1050 °C under low oxygen pressures. The annihilation of these defects has been observed from the photoluminescence and optical absorption measurements after the crystal has been subjected to a second annealing in the temperature range of about 750 °C under a reducing atmosphere. From the photoluminescence measurements, the density of these defects is found to decrease exponentially as a function of annealing time, as manifested by the reduction in the luminescent intensity. The rate of reduction in intensity is also found to increase with annealing temperature.Because the defects responsible for the luminescence are ascribed to various forms of oxygen vacancies, we believe the decrease in luminescence is due to a reduction in the oxygen vacancies resulting from the formation of copper precipitates in the crystal. The short-wave and medium-wave emissions, which are ascribed to different types of oxygen vacancies, are found to have different activation energies of diffusion.

Photoinduced transient spectroscopy (PITS) studies of samples of copper contaminated annealed semi-insulating GaAs in the temperature range of 274–384 K show two dominant levels at about Ev +0.5 eV and about Ec −0.59 eV in addition to the EL2 levels at about Ec −0.80 eV. Depth profiling using chemical etching followed by PITS measurements shows a competing process between the defects responsible for the level at Ev +0.5 eV and that at Ec −0.59 eV. The former is predominantly found near the surface and the latter is dominant in the interior. From the depth profiling results, we have determined that the diffusion constants for these two types of defects are about 4.7×10−10 cm2 s−1 and 5.2×10−10 cm2 s−1, respectively. We propose that the level at Ev +0.50 eV is due to a copper related complex and the level at Ec −0.59 eV is due to native defects. The copper related level at about Ev +0.50 eV is different from the often seen copper related defect level at around Ev +0.40 eV. The presence of these two levels would explain the variety of results reported by different workers on the deep levels attributed to copper. Photoluminescence measurements on a copper contaminated sample at 4.2 K show a peak at 1.36 eV which is due to CuGa acceptor level. This peak appears even after repeated etching of the sample, showing the presence of copper throughout the sample. Comparison data were also obtained for both ‘‘copper-free’’ annealed and unannealed samples.