Investigation to Understand the Role of Phase Variation in Red Emitting Eu³⁺-Doped Calcium Magnesium Silicate Phosphor for In Vitro Bioimaging

Eu³⁺-doped silicate phosphors are gaining significant attention for bioimaging and scaffold development due to their narrow red emission, high color purity, quantum yield (QY), and large Stokes shift. These phosphors offer several advantages over conventional imaging techniques, such as good selectivity and sensitivity, simpler operation, reduced data acquisition time, cost-effectiveness, and nondestructive imaging. The luminescence properties of these phosphors can be enhanced by modifying synthesis methods, annealing conditions, and hosts and introducing multiple dopants. This study explores a novel approach for improving luminescence by modifying the crystal structures of Eu³⁺ doped calcium magnesium silicate (CMS:Eu³⁺) phosphors for in vitro bioimaging and potential scaffold development. The synthesized diopside (CaMgSi₂O₆:<i>x</i>Eu³⁺; <i>x</i> = 10, 15, and 20 mol %), merwinite (Ca₃MgSi₂O₈:15 mol % Eu³⁺), and akermanite (Ca₂MgSi₂O₇:15 mol % Eu³⁺) phases of CMS:Eu³⁺ exhibit distinct coordination environments for Eu³⁺, leading to unique excitation wavelength tunability from ultraviolet (UV) to the visible region, high emission intensity, decay time, QY > 40%, and color purity >83%. A comparative analysis of their structural and photoluminescence properties reveals the impact of phase modifications on luminescence for in vitro bioimaging by optimizing the dopant concentration. The results indicate that CaMgSi₂O₆: 15 mol % Eu³⁺ is the most efficient phosphor for in vitro bioimaging, with the highest relative emission intensity in the red region, decay time ∼2 ms, QY ∼ 77%, and color purity ∼86%. The unique morphology of Ca₃MgSi₂O₈:15 mol %Eu³⁺ and Ca₂MgSi₂O₇:15 mol % Eu³⁺ also supports cell adhesion, suggesting their potential in scaffold development. In brief, the study highlights the potential of CMS:Eu³⁺ phosphors for in vitro bioimaging and scaffold development by modifying phases and dopant concentrations.