Etude spectrophotometrique de la serie jaune de Cu 2O aux basses temperatures

Abstract

The “yellow” series of absorption lines in Cu 2O crystals has been studied by spectrophotometric methods at different temperatures down to liquid helium. The experimental values of the oscillator strength of the absorption lines have been determinated. The oscillator strength of the first lines ( n = 2) is f 2=2.8×10 −6; the relative oscillator strength f 0(n)= f n f 2 has been calculated from experimental data for different lines. f 0( n) is however determined with a su the very first lines of the series only. Both the value of f 2 and the relative oscillator strength in the series are in good agreement with e lliott's (1) theory of forbidden exciton transitions. These arguments added to others already known (1,2) give a very solid basis to the interpretation of the “yellow” series of Cu 2O as a forbidden exciton spectrum. It has been shown that the maximum of the coefficient of absorption in a line K max decreases with the quantum number n according to a law K max ∝ 1/ n 2 for n ⩾ 3. The lines are of a very assymetric form. A parameter is introduced to characterize this property. The variation of this parameter with n is investigated. The form of the first line ( n = 2) differs very much from the form of the other lines of the series. According to our data, the life time of excitons increases with n ; this result is not inconsistent with T oyozawa's theory. (12)