Luminescence of AlN:Eu ceramics: Properties and mechanisms

Luminescence processes of AlN:Eu ceramics, prepared by high temperature spark plasma sintering method, were studied basing on material spectral characterization by measuring of photoluminescence and excitation spectra at different fixed temperatures within a region from 10 K up to room temperature, together with measurement of luminescence kinetics. In this material the Eu²⁺ ion emission at 530 nm is dominant, besides, a weak Eu³⁺ ion emission also is observed at ∼600 nm. Two main spectral regions for excitation of Eu²⁺ emission are located around 360 nm and 260 nm. Analysis of the results obtained demonstrates a presence of two luminescence mechanisms, which are originating the 530 nm emission. It was found that the 530 nm emission caused by 360 nm excitation represents the intra-center mechanism of Eu²⁺ ion luminescence, whereas the 260 nm exciting light is causing the recombination luminescence. The mechanism of the tunneling recombination luminescence is proposed. Regarding to Eu³⁺ ions, an excitation line at 464 nm was found that together with the 614 nm emission represents the intra-center luminescence. The persistent luminescence caused by Eu ions in AlN lasting within a time scale of hours is revealed.