Opposite pressure impact on electron–phonon coupling in Eu2+ and Ce3+ doped AlN

Abstract

This paper analyzes the influence of pressure on electron–lattice interactions in the 5d excited states of Ce³⁺ and Eu²⁺ in the AlN host based on pressure-dependent photoluminescence and photoluminescence excitation spectra. High-pressure measurements on AlN samples doped with Eu²⁺ and Ce³⁺ ions reveal that the Stokes shift increases with pressure for Eu²⁺ dopants and decreases for Ce³⁺ dopants. Within the interstitial sites of AlN occupied by lanthanide dopants, the effect of crystal field strength on the behavior of luminescent ions can be strongly reduced. Therefore, the observed changes in optical properties under pressure can be interpreted as occurring mainly due to electron–lattice interactions. Based on the experimental data, one can conclude that the barycenter energy of Eu²⁺ exhibits virtually no pressure-induced shift (within the experimental error), unlike Ce³⁺, which shows a pressure-dependent redshift. Our findings demonstrate the significance of the specific central ion in the lattice relaxation process.