Synthesis, optical properties, and ROS-generating performance of CdWO₄:Eu nanoparticles in potential photodynamic activity

Abstract

Europium-doped cadmium tungstate (CdWO₄:Eu) nanoparticles were synthesized via chemical precipitation, and their photophysical properties and efficiency in generating reactive oxygen species (ROS) under abiotic conditions were comprehensively investigated for potential photodynamic applications. Nanocrystals with varying Eu molar ratios (0.1–2.0 mol%) were characterized using XRD, SEM, EDX, PL, and UV-Vis spectroscopy. Singlet oxygen (¹O₂) and hydroxyl radical (⋅OH) production were evaluated using anthracene, methylene blue (MB), and rhodamine B chemical probes. The optimal europium doping level for singlet oxygen generation was determined to be 0.5 mol%. Hydroxyl radical photogeneration was further confirmed through the degradation kinetics of MB and rhodamine B under UV irradiation. Notably, the time-dependent photoluminescence decay of the nanoparticles was monitored for over 6,500 s post-excitation to evaluate their emission stability. It is important to emphasize that the present study focuses exclusively on the synthesis, material characterization, and abiotic evaluation of ROS photogeneration using chemical molecular probes. As an initial proof-of-concept investigation, critical biological safety and efficacy evaluations—including cadmium-ion leaching dynamics, cellular uptake, cell viability, dark toxicity, and in vitro/in vivo phototoxicity are beyond the scope of this work and represent essential prerequisites that must be systematically addressed in future biological studies.