Tunable Highly Efficient Photochromism and Multimodal Luminescence in (Ca,Sr)3MgSi2O8:Eu2+Solid Solutions

Abstract

Inorganic photochromic materials have been extensively studied for their potential applications in various fields such as anticounterfeiting, optical information storage, and smart windows. In this study, the tunable photochromic properties of (Ca,Sr)3MgSi2O8:Eu2+compounds, which exhibit a composition-dependent photochromic effect varying from reddish-pink to yellow, are analyzed. All investigated materials exhibit excellent photochromic efficiency, ranging from 60% in Sr3MgSi2O8to 66–69% in (Ca,Sr)3MgSi2O8:Eu2+solid solutions, reaching an unusually high value of 85% in Ca3MgSi2O8:Eu2+– exceeding values reported for other currently known wide bandgap materials. Two dominant defect-related absorbance bands centered in the blue-green and near-infrared (NIR) spectral ranges are detected using diffuse reflectance spectroscopy (DRS). Thermostimulated luminescence (TSL) analysis reveals that the dominant TSL signal, with an activation energy of 1.45 eV, shows similar excitation and bleaching behavior to the photochromic effect and is likely associated with nonparamagnetic charge trap centers. Comparison of electron paramagnetic resonance (EPR) spectroscopy and DRS measurements indicates that the photochromism in (Ca,Sr)3MgSi2O8:Eu2+is attributed primarily to the formation of F+centers, i.e., electrons trapped in oxygen vacancies, and suggests tunneling between defects. Among the investigated materials, Ca3MgSi2O8:Eu2+demonstrates the best performance by combining superior color contrast, efficient optical and thermal stimulation, and unusually deep charge traps, making it a promising candidate for practical applications.