Preliminary Study of the Exciton Absorption Spectrum of PbI2

Abstract
The absorption spectra of PbI2 at low temperature were examined after the method of Nikitine. For the band at 500 mµ, the existence of the hydrogen-like series was confirmed under the assumption that the band was composed of several components of Gaussian type, represented by the formula υ = 20, 853 − 1, 150/n2 cm−1 [20 °K]. As for the shape of each component of the band, the Gaussian form was preferable than the Lorentzian one, though the latter was expected from Toyozawa's theory. From the temperature-dependence of the band, it was concluded that (i) the rate of shift of the absorption maximum towards the shorter wavelength with the lowering of temperature is ca. 1. 5 · 10−4 ev/°K and (ii) the half value width of the band is ca. 0.02 ev, which is not sensitive to the temperature.