Upconversion Luminescence Properties of Er³⁺ Doped Yb₂Ti₂O₇ Nanophosphor by Gd³⁺ Codoping

Er³⁺ doped Yb₂Ti₂O₇ nanophosphors by Gd³⁺ codoping with nominal composition of (Er_0.05Yb_0.95−x Gd _x )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 Yb₂Ti₂O₇ nanophosphors.