Synthesis and characterization of finely dispersed phosphors doped with rare-earth metal ions for enhanced photodynamic therapy of cancer

Abstract

Finely dispersed NaBaPO4:Eu2+, NaGdF4:Eu3+, BaGdF5:Eu3+, GdF3:Yb3+, Er3+ and YF3:Yb3+, Er3+ phosphors are synthesized using a sol–gel procedure and hydrothermal method. A process is developed for obtaining NaBaPO4:Eu2+ phosphors with enhanced dispersion via sol–gel precipitation followed by a high-temperature annealing in molten NaCl. The applied annealing technique provided a 3.8-fold decrease in the phosphor particle size and 11-fold increase in the finely dispersed (less than 1 μm) fraction compared with the phosphors prepared using a conventional sol–gel method. In addition to already known luminescence centers comprising Eu2+ ions located in NaBaPO4 lattice sites with coordination numbers 10 and 12, these phosphors are found to contain two more types of luminescence centers supposedly corresponding to Eu2+ ions in the same positions locating on the phosphor particle surface. According to the obtained data, the energy levels of luminescence centers in the NaBaPO4:Eu2+ phosphor are summarized in a chart. NaGdF4:Eu3+ phosphor is shown to be mostly appropriate for X-ray stimulated photodynamic therapy (PDT), while GdF3:Yb3+, Er3+ phosphor is promising for IR-activated PDT. The efficiency of 980 nm IR laser-induced generation of active oxygen by a medicine involving the YF3:Yb3+, Er3+ phosphor, and Radachlorin photosensitizer is studied. A finely dispersed NaBaPO4:Eu2+ phosphor is synthesized using a modified sol-gel method and studied to make a detailed energy chart of luminescence centers, including specific energy levels of surface sites. A nanosized (particles below 100 nm) YF3:Yb3+,Er3+ phosphor synthesized via hydrothermal technique is found to be useful for photodynamic therapy of abdominal cancer in couple with Radachlorin photosensitizer by generating active oxygen upon IR stimulation.