Scintillating and Photoluminescent Ratiometric and Visual Luminescence Thermometry Based on the Ce ³⁺ -Doped Eutectic Structures

A next-generation class of dual-phase, multifunctional photoconversion and thermal sensing materials has been developed using Ce³⁺-doped YAG-YAP eutectic crystals, synthesized via directional solidification at variable rates (0.1-0.9 mm/min) to precisely tailor phase morphology and dopant distribution. Structural and compositional analyses revealed a lamellar microstructure comprising alternating garnet (Y₃Al₅O₁₂, YAG) and perovskite (YAlO₃, YAP) domains, with Ce³⁺ ions preferentially partitioned into the garnet phase at elevated solidification rates. Systematic control of domain sizes was achieved by modulating the growth rate. Slower growth resulted in larger domains that enabled near-complete transmission of blue light through YAP, whereas faster growth produced finer structures that led to increased scattering and absorption of blue light. This morphology-driven optical tunability enabled dynamic control over the correlated color temperature (CCT), ranging from cool to warm white emissions. Beyond structural engineering, the eutectics demonstrated dual-mode thermal sensing via ratiometric luminescence thermometry under both photoluminescence (PL) and X-ray-induced scintillation excitation. Excitation modality significantly affected thermal sensitivity due to distinct charge transport and energy transfer dynamics. Under PL, the relative sensitivity reached 0.47% K^-1, while scintillation-based excitation achieved an enhanced sensitivity up to 1.1% K^-1. Crucially, the scintillation mode permits passive, remote temperature monitoring without external optical excitation, activated solely by ambient ionizing radiation. These capabilities position Ce³⁺-doped YAG-YAP eutectics as promising candidates for advanced thermal sensing in extreme environments, including nuclear reactors, aerospace systems, and high-energy particle detectors.