Multiband MgAl<sub>0.05</sub>Ge<sub>0.95</sub>O<sub>3</sub>:0.3%Pr<sup>3+</sup> Persistent\nPhosphor as Efficient Tracers\nin Crude Oil Emulsions

The use of fluorescent nanoparticles (NPs) for tracing\npurposes\nin oilfields encounters challenges due to background interferences\nunder constant external excitation caused by organic residues present\nin crude oil. This results in insufficient sensitivity and lower tracer\ndetection limits in the crude oil/water emulsions. In this study,\nwe present the synthesis of persistent luminescent NPs, showcasing\ntheir remarkable application as tracers in crude oil. The multiband\nMgAl<sub>0.05</sub>Ge<sub>0.95</sub>O<sub>3</sub>:0.3%Pr<sup>3+</sup> persistent NPs were synthesized via the sol–gel method. Through\nmeticulous experimentation and analysis, our study unveils a novel\navenue for efficient and lasting traceability in crude oil. The synthesized\nNPs emit light across the visible, near-infrared, and shortwave infrared\nregions, allowing for versatile detection. The unique luminescent\nproperties of these NPs, particularly their ability to persist in\nemitting light without a continuous external excitation, enable their\neffective use as tracers in crude oil/water emulsions where background\nfluorescence typically poses a significant challenge. By employing\nthese persistent NPs in background fluorescence-free conditions, we\nachieve ultrahigh sensitivity in detecting these NPs in crude oil.\nOur research reveals that the doping of Al<sup>3+</sup> ions significantly\nenhances both the afterglow intensity of MgGeO<sub>3</sub>:0.3%Pr<sup>3+</sup> phosphor and the afterglow decay time of Pr<sup>3+</sup> emission. This characteristic enables the re-excitation of MgAl<sub>0.05</sub>G<sub>0.95</sub>O:0.3%Pr<sup>3+</sup> NPs within the emulsion,\nallowing for repeated spectral and imaging acquisition. This high\nsensitivity not only facilitates precise imaging of NPs in crude oil\nbut also enables long-term monitoring in real-time, offering valuable\ninsights for oilfield operations.