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

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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.