Unveiling The Distribution and Dynamic Behavior of Multi-Valent Chromium Ions in Li(Sc_1−xIn_x)O₂:Cr Phosphors via In-Depth X-Ray Characterization

Cr³⁺-doped inorganic compounds have played an important role in the development of near-infrared optical materials. However, the presence and distribution of multi-valent Cr ions remains unclear. In this study, we examined a series of Li(Sc_1−xIn_x)O₂ phosphors doped with Cr³⁺ using X-ray techniques from National Synchrotron Radiation Research Center. Through high-resolution synchrotron X-ray diffraction, we identified two closely related phases within Li(Sc_1−xIn_x)O₂. Raman spectra also confirmed distinctive scattering patterns for the two end-members of the compositional range, consistent with our XRD results. Further investigation using Cr K-edge X-ray absorption near edge structure and extended X-ray absorption fine structure techniques revealed the prevalence of Cr⁶⁺ ions in the initial samples. However, a significant shift occurred towards Cr³⁺ dominance upon water washing. We also used X-ray fluorescence and X-ray excited optical luminescence methods to analyze the source and spatial distribution of Cr³⁺ and Cr⁶⁺ ions in both as-prepared and washed samples. Our analysis indicated that Cr⁶⁺ ions aggregate within the material, while Cr³⁺ ions exhibit a more uniform dispersion. By utilizing photoluminescence, decay curve, and lineshape analyses, we were able to understand the electron-lattice interactions responsible for the optical properties. Our study explains the multi-valent, low-concentration ion distribution in solid-state materials and provides valuable insights into precise methodologies for discerning subtle alterations in crystal structures, contributing to the development of tailored optical materials.