PRESSURE-DEPENDENCE OF GAMMA-EXCITON IN ALKALI BROMIDE THIN-FILMS

Pressure dependence of optical absorption spectra of Gamma excitons in alkali bromide thin films, NaBr, KBr and RbBr, was measured at room t emperature. The exciton energies showed linear blue shifts while the a bsorption intensities decreased with increasing pressure. In order to further understand the experimental results; the pressure dependence o f the absorption intensities is discussed in terms of the pressure dep endence of Bohr radius by Elliott's theory and exchange interaction be tween electron and hole by Onodera and Toyozawa's theory. We speculate that the Bohr radii increase and the exchange energies decrease as th e pressure increases for the Gamma 3/2 and the Gamma 1/2 excitons in t he alkali bromides.