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.

Graphic abstract

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.