Transformation of LaOF into LaF3 owing to Al3+ in luminescent Eu3+-doped crystalline powders

Abstract

Conversion of LaF₃ into LaOF has been demonstrated in the literature through heat treatment of the samples. In this work, we investigated the possibility of converting LaOF into LaF₃ using Al³⁺ in a combustion synthesis technique. The conversion was proposed by taking advantage of the affinity that aluminium has for oxygen. The morphological study via scanning electron microscopy has shown an increase in the porosity of the samples with the inclusion of aluminium. X-ray powder diffraction data analysis demonstrated complete crystallization and conversion of LaOF into LaF₃ due to the presence of aluminium. A small fraction of LaAlO₃ has been detected and it confirms that aluminium bonds with oxygen, as expected. The samples were also doped with the rare-earth ion europium as a luminescence probe. Stokes photoluminescence was produced using UV light (λ = 355 nm) and the spectral analysis of Eu³⁺ 4f–4f electronic transitions has confirmed that LaOF is converted into LaF₃. The measured luminescence lifetimes of reactant and product are characteristic of Eu³⁺ in the compounds LaOF and LaF₃.