Phonon-assisted optical bands of nanosized powdery SrAl2O4:Eu2+ crystals: Evidence of a multimode Pekarian

Abstract A stoichiometric powder composed of nanosized grains of SrAl 2 O 4 :Eu 2+ was synthesized by combustion method at 500 °C with the subsequent calcination at 1000 °C. The zero-phonon line position, parameter of the Stokes shift, heat release factor and effective phonon energy were studied experimentally and analyzed in the framework of the multimode Pekar–Huang–Rhys model. Experimental data show that the optical 4 f – 5 d transitions in Eu 2+ ion exhibit a broad asymmetric electron–vibrational bands with a pronounced structure near the maxima. The form-function of the absorption and luminescence bands are theoretically analyzed in the framework of the model of the linear electron–vibrational interaction assuming strong coupling with the local vibration (estimated Pekar–Huang–Rhys parameter a = 2 S = 10 and frequency ℏ ω = 509 cm − 1 ) and relatively weak interaction with the crystal phonons. The last results in an effective temperature dependent broadening of the discrete lines corresponding to the local vibrations and to a specific shape of the whole phonon assisted band (multimode Pekarian). Providing specific interrelation between the key parameters the calculated absorption and luminescence bands exhibit peculiar temperature dependent structured peaks in a qualitative agreement with the experimental data.