Matrix-dependent high-contrast photochromism in Eu-doped M3MgSi2O8 (M = Ca, Sr, Ba)†

The photochromic properties and charge transfer processes were studied in novel Eu-doped M₃MgSi₂O₈ (M = Ca, Sr, Ba) compounds. These materials exhibit vivid color changes upon irradiation with UV light, resulting in orange, reddish-pink, and green colors. The introduction of europium ions enhances photochromic efficiency and shifts excitation peaks to lower energy ranges. Analysis of diffuse reflectance and electron paramagnetic resonance spectra reveals the formation of both paramagnetic and non-paramagnetic defects, with the dominant signals attributed to electron centers, likely F⁺-type centers. The Eu²⁺ → Eu³⁺ charge transfer during irradiation indicates that Eu²⁺ acts as a hole center. These findings contribute to a better understanding of the mechanisms underlying photochromism in these materials and highlight their potential for practical applications.