Effect of Li+ Ions Doping on Microstructure and Upconversion Emission of Y2Ti2O7:Er3+/Yb3+ Nanophosphors Synthesized Via a Sol–Gel Method

Er3+/Yb3+/Li+-tridoped Y2Ti2O7 nanophosphors were synthesized via a facile sol–gel process. The samples were characterized by the inductively coupled plasma atomic emission spectrometer (ICP-AES), X-ray diffraction (XRD), transmission electron microscopy (TEM), and infrared-to-visible upconversion (UC) luminescence spectra. XRD analysis showed that the crystallization temperature of pyrochore-type Y2Ti2O7 was reduced due to the flux effect of Li+ ions, whereas TEM measurements confirmed that the particles size of (Y0.815Er0.01Yb0.075Li0.10)2Ti2O7 was about 30–40 nm when calcining at 800°C for 1.0 h. The calcining temperature and Li+ ion concentration dependence on UC luminescence spectra were investigated. It was found that, when incorporating 10.0 mol% Li+ ion, the UC red and green emission intensity was drastically increased by a factor of 18.6 and 8.3, respectively. The enhancement of UC emission may be mainly attributed to the modification of local symmetry around Er3+ ions by tridoping Li+ ions. And also, the pump power dependence of the emission intensity was investigated to understand the fundamental UC mechanism.