VACUUM-ULTRAVIOLET CHARACTERIZATION OF SAPPHIRE, ALON, AND SPINEL NEAR THE BAND-GAP

Ultraviolet optical properties near the edge of transparency (just abo ve and below the band gap) of polycrystalline ALON (aluminum oxynitrid e, Al23O27N5) and spinel are not well characterized. The edge of trans parency is commonly found to obey Urbach's rule, and this is the case for single-crystal sapphire and polycrystalline ALON and spinel as wel l. Room-temperature transmission and reflection measurements are made from 2500 to 1150 angstrom on these materials and the corresponding ab sorption coefficient at the band gap is represented by Urbach's rule.