Developing near-infrared long-lasting phosphorescence of Yb3+ through a medium: insights into energy transfer in the novel material Zn1.98Li0.02P2O7:Yb3+

Abstract

Near-infrared (NIR) long-lasting phosphorescence (LLP) phosphors have potential applications in biological and military fields. However, the properties of these phosphors are insufficient to satisfy the demands. Herein, we report a series of novel LLP phosphors Zn_1.98−xLi_0.02P₂O₇:xYb³⁺ with strong NIR LLP. By investigating the O–Yb³⁺ charge transfer (CT) band and host thoroughly, it can be confirmed that distinct photoluminescence (PL) of the two can be realized by selecting an appropriate excitation. For NIR emission, considering that the emission of Yb³⁺ originates from the characteristic 4f–4f transition between ⁴F_5/2 and ⁴F_7/2 levels and the difference between these two levels is too small to be excited by UV light, it is practicable to use the energy transfer of the host rather than that of the O–Yb³⁺ CT band as its energy level does not match with that of Yb³⁺. LLP is different from PL of the O–Yb³⁺ CT band, host or Yb³⁺, and it is strongly dependent on the appropriate depths of the traps; therefore, the selection and regulation of the traps are crucial. Considering the practicability and the demand of NIR LLP materials, we focus on how to excite Yb³⁺ and obtain LLP.