Calculation ofF-Band Peak Energy in CsF

A calculation of the $F$-band peak energy in CsF has been made using a quantum-mechanical self-consistent-field method of the variation type. This calculation gave a value of 1.71 eV for the CsF absorption-band peak. This result is only 2.3% lower than the 1.75-eV peak of the triplet absorption measured by Hughes and Rabin in x-ray colored CsF crystals. Similar calculations have been made for $F$-band peaks in LiF, NaF, KF, and RbF and numerical results are presented. Comparison of existing experimental data on the alkali fluorides and the present theoretical results lends credence to the suggestion made by Hughes and Rabin that the triplet absorption at 1.95, 1.86, and 1.75 eV in CsF is due to the $F$ center. The absorption peak observed at 2.18 eV in CsF could not be considered as a candidate for the $F$-band, since it is 21.5% higher than the calculated value.