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Aqueous solutions of La1−xPrxPO4 nanoparticles: microwave‑assisted hydrothermal synthesis, X‑ray excited UV‑C luminescence, and colloidal properties
Nanoparticles (NPs) exhibiting X-ray excited UV-C luminescence can be used in radia tion therapy to deactivate cancer cells through pho tochemical reactions of DNA with UV-C quanta. Colloidal solutions of monoclinic La1−xPrxPO4 NPs (x = 0.01–0.3), luminescent in the UV-C range (220–280 nm), with different morphologies, from nanofiber (diameter and length not larger than 15 and 600 nm, respectively) to short nanorod (diameter and length not larger than 8 and 35 nm, respectively), were obtained by a microwave-assisted hydrothermal method. For possible biomedical use, the synthe sis parameters (pH = 8, anion excess coefficient = 2) were determined, at which nanorods of suitable sizes (diameter and length not larger than 10 and 80 nm, respectively) with the brightest UV-C luminescence among all synthesized nanorods were obtained. A gradual increase in the optimal concentration of Pr3+ ions with maximum luminescence brightness from 4 mol-% for nanofibers to 6 mol-% for short nanorods was established. The shift of the intensity ratio of UV-C transitions toward the long-wave 4f15d1→3H6 transition was shown for nanofibers, whereas for nanorods all 4f15d1→3H4,5,6 transition intensities were approximately equal. A new laser ultramicros copy method based on the detection of elastically scattered light with subsequent nanoparticle tracking analysis was used to calculate the hydrodynamic radii and to monitor the colloidal behavior of NPs in pH modified aqueous media. The highest sedimentation and aggregation stability of NPs was found in an acidic medium (pH = 4), and temporary stability was also found in alkaline media (pH = 8, 10).