Incorporation of the Ce3+ activator ions in LaAlO3 crystals: EPR and NMR study

TL;DR

This study investigates how Ce3+ ions incorporate into LaAlO3 crystals using EPR and NMR techniques, revealing local structural changes and interactions that influence the material's optical properties.

Contribution

It provides detailed EPR and NMR characterization of Ce3+ incorporation in LaAlO3, highlighting local symmetry lowering and Fermi contact interactions affecting optical behavior.

Findings

Ce3+ g tensor has orthorhombic symmetry even in trigonal phase.

139La chemical shift increases linearly with Ce concentration.

Crystal structure near Ce ions is modified, affecting optical properties.

Abstract

This work reports the results of EPR and NMR study of the Ce3+ incorporation in LaAlO3 single crystals grown by the micro-pulling-down method in the range of the Ce concentrations from x=0.1 at.% up to 100 at.%. From EPR measurements, Ce3+ g tensor parameters were obtained as function of Ce concentration. The g tensor has orthorhombic symmetry even in the trigonal phase (x < 10 at.%) suggesting that the incorporation of Ce at La site lowers lattice symmetry near this ion. The local properties of the La1-xCexAlO3 crystals were further studied by 27Al and 139La high-resolution NMR measurements. It was found that 139La chemical shift has the Fermi contact interaction origin. It linearly increases with Ce concentration up to 165 ppm at x = 0.5. Due to this strong Fermi contact interaction, separated peaks corresponding to different Ce-O-La spin transfer passways are resolved in the 139La NMR spectra. On the other hand, no Fermi contact interaction is visible in 27Al NMR spectra. However, these spectra contain satellite peak which intensity linearly increases with increase of Ce concentration leaving position of this peak unchanged. This was interpreted as manifestation of crystal structure modification in vicinity of Ce ions in agreement with EPR data. Thus, optical properties of Ce3+ in LaAlO3 will be namely determined by the local crystal structure near this ion.