A novel photoluminescence theory and design rule based on solution entropy for rare earth ion doped alkaline metal silicates

This paper introduces an innovative theory for customizing photoluminescence (PL) emission wavelengths in rare earth ion (Eu²⁺⁾ doped alkaline earth metals (Ca, Mg) silicates, rooted in the entropy of fusion and configurational entropy of congruent and incongruent silicates, respectively, aiming to reveal dynamic deformation of the tetrahedral SiO₄ ligand within these materials. Using FactSage, we computationally calculate the fusion entropy of congruent silicates in the CaO-MgO-SiO₂ system. Synthesized ternary silicates confirm our theory by highlighting correlations between lower/higher fusion entropy (for congruent) and configurational entropy (for incongruent) silicates, leading to red/blue shifts in PL emission wavelengths. In binary silicate systems, we observe an inverse correlation between PL emission wavelengths and fusion entropy of congruent silicates or pseudo-congruent silicates like MgSiO₃, whose solid-liquid decomposition temperature is close to its melting point. Furthermore, the non-ideal liquid phase entropy of incongruent silicates positioned between congruent CaMgSi₂O₆ (Pyroxene) and congruent Ca₂MgSi₂O₇ (Akermanite) in the MgO-CaO-SiO₂ ternary phase diagram comprehensively explains diverse PL emission wavelengths. Beyond its scholarly impact, this work expands perspectives in lighting and photonic research, opening an exciting frontier in entropy-lighting research and enabling predictions of host chemical composition and tunable PL emission wavelengths, particularly relevant to LED technologies.