Monitoring the t → m Martensitic Phase Transformation by Photoluminescence Emission in Eu³⁺-Doped Zirconia Powders

Abstract

In this work, we demonstrate that the martensitic t → m phase transformation of ZrO₂ powder stabilized with Eu³⁺ and Eu³⁺/Y³⁺ ions, can be effectively monitored by photoluminescence (PL) spectroscopy. As the luminescent properties of Eu³⁺ from within a host lattice are strongly influenced by the coordination geometry of the ion, we used the emission spectrum to monitor structural changes of ZrO₂. We synthesized Eu³⁺-doped and Eu³⁺/Y³⁺-codoped samples via the coprecipitation method, followed by calcination. We promoted the martensitic transformation by applying mechanical compression cycles with an increasing pressure, and deduced the consequential structural changes from the relative intensities of the ⁵D₀ → ⁷F₂ hypersensitive transitions, centered, respectively, at 606 and 613 nm whether the Eu³⁺ is in the eightfold coordinated site of the tetragonal phase or in the sevenfold coordinated site of the monoclinic phase. We suggest that the unique emission profile for Eu³⁺ ions in different symmetry sites can be exploited as a simple analytical tool for remote testing of mechanical components that are already mounted and in use. The structural changes observed by PL spectroscopy were corroborated by X-ray powder diffraction (XRPD), with the phase compositions and volume fractions being determined by Rietveld analysis.