Ultraviolet and visible upconversion emissions in Er^3+-Yb^3 + doped titanium dioxide nanopowder under the 980 nm laser diode excitation

Er^3 +-Yb^3 + co-doped titanium dioxide upconversion nanoparticles were synthesized by sol-gel method. White upconversion emissions were observed after excitation of nanoparticles with 980 nm Near-Infrared laser diode. Upconversion emissions consist of red (640-690 nm), green (520-570 nm), and blue (408 nm) emissions. Ultraviolet upconversion emissions were also detected with wavelength about 210 nm. Ultraviolet emissions are probably the results of relaxation from 2Ii3/2 (220 nm) and 2Li5/2 (210 nm) states to 4Ii5/2- Visible and ultraviolet emissions of these nanoparticles can be used in photodynamic therapy. High penetration of Near-Infrared light into the body tissue makes these nanoparticles appropriate for aiming tumors in deeper tissues in comparison with older methods of photodynamic therapy.