Hydrothermal synthesis and characterization of nano-sized phosphors based on rare-earth activated yttrium compounds for photodynamic therapy

Finely dispersed Y₂O₃:Eu, Y₂Si₂O₇:Eu, YF₃:Ce and YF₃:Eu luminescent phosphors are synthesized using a hydrothermal method. A process is developed for obtaining Y₂O₃:Eu phosphors with a reduced particle size by hydrothermal precipitation with the addition of an inert finely dispersed filler (Aerosil) followed by rapid thermal annealing (RTA). Another process is suggested for the synthesis of finely dispersed Y₂Si₂O₇:Eu phosphor via hydrothermal precipitation followed by microwave annealing. The effect of the synthesis conditions on the properties of YF₃:Ce and YF₃:Eu nanosized phosphors is studied and hydrothermal processing conditions were determined so as to provide the adjustment of their luminescence spectra due to the variation of the activator valency (Eu³⁺/Eu²⁺ and Ce³⁺/Ce²⁺). Besides earlier defined luminescence centers comprising Eu²⁺ ions in orthorhombic and cubic coordination positions of YF₃ crystal lattice, the studied phosphors involve two additional types of luminescence centers relating to Eu(II), supposedly corresponding to Eu²⁺ in the same coordination positions located on the surface of the phosphor particles. Using the obtained data, an energy chart of Eu(II)-based luminescence centers in YF₃:Eu nanosized phosphors is suggested. The resulting nanoscale particle size and luminescence spectra features of the synthesized phosphors YF₃:Ce and YF₃:Eu make them potentially useful for photodynamic therapy of cancer in combination with the photosensitizer Rose Bengal. The composition involving the synthesized Y₂O₃:Eu phosphor and photosensitizer Photoditazine was shown to provide an effective destruction of tumor cell cultures.