Insight into Green-Synthesized All-in-One Multifunctional Nanophosphor: Achieving Multicolor Luminescence, Optical Thermometry, Thermoluminescence, Bioimaging, Anticounterfeiting, and X-ray Scintillation Applications

Designing cost-effective, stable, and customizable multifunctional phosphors is pivotal for technological innovation and is a boon for a sustainable society. This article reports green, surfactant-free, low-temperature synthesis of Azadirachta indica-derived Tb3+,Eu3+:CeF3 nanophosphors exhibiting versatile optical functionalities. Pure phase β-CeF3 with well-resolved crystallographic parameters was confirmed by X-ray diffraction and Rietveld refinement. The Tb3+, Eu3+ codoping enabled efficient energy transfer, producing excitation-dependent tunable multicolor emission across visible spectrum. Combined emissions from Tb3+ (5D4→7Fj) and Eu3+ (5D0→7Fj) provide a majorly intense, saturated orange light with emission intensities 5D4→7F4 < 5D0→7F2 < 5D0→7F1 < 5D4→7F6 < 5D4→7F5. The phosphor responds efficiently to X-rays, UV–Vis. radiation, and β-irradiation (90Sr/90Y), highlighting its multifunctionality in diverse optoelectronic domains, including radioluminescence (RL), photoluminescence (PL), thermoluminescence (TL), and optically stimulated luminescence (OSL). TL exhibits three well-resolved peaks centered at 119, 206, and 312 °C with stability under 3–15 Gy doses, confirming its suitability for radiation dosimetry. RL studies on thin films displayed a linear intensity dependence on X-ray tube voltage (40–100 kV at 4 mA) and current (1–5 mA at 100 kV), demonstrating efficient X-ray to visible light conversion. Biological studies via MTT assay reveal selective cytotoxicity toward MCF-7 breast cancer cells over A549 lung cancer cells, while bioimaging at 15.75 μg/mL confirms cellular uptake and nuclear fragmentation, highlighting theranostic and bioimaging potential. UV-excited persistent luminescence demonstrates high-contrast anticounterfeiting marks for security information encryption. Luminescence thermometry based on the fluorescence intensity ratio (FIR) of Tb3+, (5D4→7F5, 541 nm), and Eu3+ (5D0→7F2, 613 nm) follows ln (FIR) = 3.81–962.55/T, and ΔE ∼ 668.97 cm–1, providing maximum relative and absolute sensitivities of 1.049% K–1 (at 303 K) and 0.194% K–1 (at 358 K), respectively. Collectively, Tb3+,Eu3+:CeF3 nanophosphors exhibit thermal stability, multicolor emission tunability, customizability, and promising optical properties significant for lighting, dosimetry, X-ray scintillation, anticounterfeiting, theranostics, bioimaging, and luminescent thermometry.