Optical investigation of divalent europium in the alkali chlorides and bromides

Abstract

Detailed optical absorption data are reported for the divalent europium ion in NaCl, KCl, RbCl, KBr, RbBr, and KI single crystals at 300 and 77 K. Values of the oscillator strength are calculated for all the observed bands in the optical spectra at both temperatures. It is established that the optical spectra are well accounted for by a strong crystal field split 5d electron having a Coulomb interaction with the 4f⁶ core about one‐half the free ion value. It is also shown that the measured 10 Dq cubic field splitting of the 4f⁶ 5d configuration into its t_2g and e_g components is in accord with the expected order of the fields exerted by the different crystal media. In addition, calibration constants are reported for determining the Eu²⁺ concentration in KBr, RbBr, and KI single crystals by optical techniques, without destroying the sample.