Zero-Phonon Transition and Fine Structure in the Phosphorescence of Fe3+ Ions in Ordered and Disordered LiAl5O8

Abstract

Phosphorescence and excitation spectra have been measured in Fe³⁺‐doped ordered and disordered LiAl₅O₈. A good fit with the Tanabe‐Sugano diagram for a high spin d⁵ configuration with B=644 cm⁻¹ and C=2960 cm⁻¹ has been obtained. From the calculated 10 Dq value of 8000 cm⁻¹ and a comparison with the excitation spectra of Fe³⁺ in β‐NaAlO₂ it has been shown that the spectra are due to Fe³⁺ ions in tetrahedral interstices. A sharp zero‐phonon transition has been observed in the low‐temperature phosphorescence and excitation spectra of the ordered phase of LiAl₅O₈ and its occurrence was found to be correlated with an anomalously small Stokes shift of 500 cm⁻¹. X‐ray powder diffraction, phosphorescence, and ESR spectra show that there exist only two phases of LiAl₅O₈, an ordered and a disordered phase. Evidence is given that the previously postulated metastable phase is a phase with incomplete ordering.