desorption spectroscopy. Potassium iodide Apker followed up his work on the photoelectric effect with an investigation of the photoelectric properties of the alkali halides, particularly potassium iodide. In potassium iodide, an ionic crystal, some iodide ions can be removed and their vacant places will be filled by electrons. Called "F-Centers," these defects absorb visible and ultraviolet light, coloring the crystals at photon energies where they are usually transparent. Additionally, the absorption of visible radiation can free trapped electrons inside the crystal and produce photoconductivity. Apker found that in addition to visible radiation, near-ultraviolet radiation also produces photoconductitivty. Deeper into the ultraviolet spectrum, however, potassium iodide has a strong absorption line due to the formation of chargeless particles called excitons. These excitons transfer energy to the electrons in the F-Centers with remarkably high efficiency, and these excited electrons are excited from the crystals in exciton-induced photoemission. Apker observed the same sort of behavior in other crystals such as barium oxide. Legacy In 1978, Apker's wife and colleague Jean Dickey Apker established the LeRoy Apker Award of the American Physical Society in memory of Apker. The award is presented to two college undergraduates each year. Bibliography References 1915 births 1970 suicides Experimental physicists Scientists from Rochester, New York University of Rochester alumni Oliver E. Buckley Condensed Matter Prize winners Suicides by firearm in New York (state)