Upconversion Luminescence Properties of Er3+ Doped Yb2Ti20 Nanophosphor by Gd3+ Codoping

Er3+ doped Yb2Ti207 nanophosphors by Gd3+ codoping with nominal composition of (Er0.05Yb0.95-xGd3+)2Ti2O7 (x = 0, 0.2, 0.4, 0.6, 0.8, and 0.95) have been prepared by sol-gel method. Er3+-Gd3+ codoped Yb2Ti2O7 was characteristic of a typical face-centered cubic crystal phase, and the unit cell parameter increased linearly with the increase of Gd3+ concentration. Under a 976 nm laser diode excitation, both green and red upconversion emissions were observed and the upconversion emissions were enhanced significantly by Gd3+ codoping, showing the strongest green and red emissions at 80 mol% Gd3+ codoping. The intensity ratio of green to red emissions (Igreen/Ired) increased monotonously with the increase of Gd3+ concentration. The energy transfer between Yb3+ and Er3+ and the variation of local crystal field symmetry of Er3+ by the substitution of Yb3+ by Gd3+ ions led to the improvement of upconversion properties of Er3+-Gd3+ codoped Yb2TiO7 nanophosphors.