Energy Transfer Mechanisms in Yb³⁺-Doped GdVO₄ Near-Infrared Downconversion Nanophosphor

Yb³⁺-doped GdVO₄ nanophosphor was prepared by the co-precipitation method. Under ultraviolet (UV) light excitation, strong near-infrared (NIR) emission of Yb³⁺ (²F_5/2 → ²F_7/2) around 980 nm was observed. Owing to the host absorption of GdVO₄, a broad excitation band ranging from 250 to 350 nm was recorded when the Yb³⁺ emission was monitored, which suggests an efficient energy transfer from the host to the Yb³⁺ ions. The concentration dependence of the visible vanadate emission and the Yb³⁺ emission was investigated. The decay curve of the vanadate emission was measured under the excitation of a 266 nm pulsed laser. The decay time of the vanadate emission at 500 nm was remarkably reduced by introducing Yb³⁺, further verifying that the energy transfer from the vanadate host to the Yb³⁺ ions was very efficient. Cooperative energy transfer (CET) is discussed as the possible energy transfer process. The temperature dependence of the emission intensity and decay time were also investigated for our further discussion.