Optische Eigenschaften von natürlichen und künstlichen Bleichromateinkristallen

Abstract

Out of solution artificial PbCrO4-single-crystals, monoclin modification, equal to natural Crocoit have been produced. The optical constants for natural and these artificial crystals have been found to be equal by measurements of reflectivity and transmission with unpolarised light in the range 0.3 — 15 µm perpendicular to the (110) -plain. Between 1 and 8 µm the refractive index is constant (n = 2,1). In this region some absorption bands occur (2.8 µm corresponding to the donator activation energy of 0.44 eV and 6 μm). At 0.45 µm there is another absorption band but no absorption edge, which was expected with respect to the photoconductivity. Above 8 µm the optical constants are determined by the reststrahlen band at 11.3 μm. The absorption of free charge carriers is discussed because leadchromate in the literature is known to be a purely electronical conductor. An influence of the free charge carriers in the tested spectral range could not be recognized. From this fact it is possible to give some estimations about the conductivity mechanism respectively the mobility of the free electrons.