Search forF-Center Luminescence

Measurements have been made on the quantum efficiency of luminescence from $F$ centers in x-rayed LiF and additively colored KCl at 4°K. In the wavelength range from 3000A to 20 000A an upper limit of 3 percent efficiency is found for the LiF $F$-band emission, if it exists. At 25 000A the upper limit is 10 percent. Similar results are found for $F$ centers in KCl in the wavelength range from 6500A to 25 000A. These results are in disagreement with theoretical predictions that the $F$ center should luminesce with high efficiency in the wavelength region near 10 000A.