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

Finely dispersed Y 2 O 3 :Eu, Y 2 Si 2 O 7 :Eu, YF 3 :Ce and YF 3 :Eu luminescent phosphors are synthesized using a hydrothermal method. A process is developed for obtaining Y 2 O 3 :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 Y 2 Si 2 O 7 :Eu phosphor via hydrothermal precipitation followed by microwave annealing. The effect of the synthesis conditions on the properties of YF 3 :Ce and YF 3 :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 (Eu 3+ /Eu 2+ and Ce 3+ /Ce 2+ ). Besides earlier defined luminescence centers comprising Eu 2+ ions in orthorhombic and cubic coordination positions of YF 3 crystal lattice, the studied phosphors involve two additional types of luminescence centers relating to Eu(II), supposedly corresponding to Eu 2+ 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 YF 3 :Eu nanosized phosphors is suggested. The resulting nanoscale particle size and luminescence spectra features of the synthesized phosphors YF 3 :Ce and YF 3 :Eu make them potentially useful for photodynamic therapy of cancer in combination with the photosensitizer Rose Bengal. The composition involving the synthesized Y 2 O 3 :Eu phosphor and photosensitizer Photoditazine was shown to provide an effective destruction of tumor cell cultures. Graphical abstract A hydrothermal procedure is developed for obtaining YF 3 :Eu nanosized phosphors with adjustable luminescence spectra due to the activator valence variation (Eu 3+ /Eu 2+ ). An energy chart for Eu 2+ -based luminescence centers is suggested for the considered phosphors.