OPTICAL STUDIES OF NACL SINGLE CRYSTALS IN 10 EV REGION .2. SPECTRA OF CONDUCTIVITY AT LOW TEMPERATURES ABSORPTION CONSTANT AND ENERGY LOSS

Kramers-Kronig analysis was made on the reflectivity spectra of NaCl single crystals in the region 6eV to 12eV for temperature range from 10°K to 573°K. The spectra of absorption constant and energy loss are reported for the temperature range from 10°K to 573°K and compared with those obtained on thin film specimens. The spectra of complex dielectric constant, complex refractive index and conductivity are presented at temperatures of 10°K, 78°K and 298°K. The analysis of σ-spectrum in the region of chlorine doublet and the plateau near the step leads to the conclusion that the spectrum in this region consists of absorptions due to hydrogen like series of exciton. Each of the chlorine doublet standing for n=1 state exciton lines can be fitted with a suitable asymmetric Lorentzian function having a positive degree of asymmetry. The oscillator strengths of (3/2, 1/2)- and (1/2, 1/2)- components are estimated at 0.212 and 0.252 at 10°K, respectively. The exchange interaction between electron and hole of an exciton and the threshold value of photoelectron emission from single crystals are discussed on the basis of the present experimental results. The peak at 11.5 eV is interpreted as being due to the exciton formation associated with the transition from highest valence bands to excited energy bands resulting from 3d sodium states. © 1968, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.