512Т. L. LOUCKS 143 changes in the exchange potential should also affect the results for Mo and we have seen (Ref. 8) that this is not necessary to get agreement with experiment. This, coupled with the fact that Mo and W differ in several experiments, leads us to attribute these differ ences mainly to relativistic effects.The absorption and reflection spectra of ZnO crystals have been studied in the region of intrinsic absorp tion, and the data have been interpreted in terms of the wurtzite model given by Birman. Three intrinsic exciton transitions have been observed, one associated with each of the three valence bands. Several boundexciton transitions have also been observed. The data have been analyzed, and a number of exciton param eters in ZnO are reported which are somewhat modified from those previously reported.

Polarized Brillouin scattering measurements were carried out for a bulk ZnO single crystal. The whole set of elastic stiffness constants was determined to be c11=19.0, c12=11.0, c13=9.0, c33=19.6, c44=3.9, and c66=4.0 in units of 1011 dyn/cm2. The relationships between photoelastic constants at wavelength of 514.5 nm were also obtained: p11, p13, p44, and p66=1.8, 2.3, 0.50, and 0.38, respectively, relative to p12.

No abstract

No abstract