Photoluminescence in AlN: Macro-size and nano-powder

Photoluminescence (PL) properties in AlN are studied when size of polycrystalline grains is reduced from macro-size (AlN ceramics and macro-size powder) to nano-size (nano-powder). It was found that in all these materials within the UV-blue spectral region two PL bands are observed at ∼400 nm (caused by the oxygen-related defects) and at 480 nm (with unknown defect structure) but the ratio of their intensities depends on the grain size. Reduction of AlN grain size results in decrease of the 400 nm band and increase of the 480 nm band. It allows the following conclusions: i) reduction of AlN grain size results in decrease of oxygen (the native impurity of AlN) content in the crystalline lattice, and ii) the defects responsible for 480 nm PL band could originate from the material surface.