Enhanced energy transfer and near-infrared luminescence by crystal field regulation in Zn3Ga2GeO8:Cr3+,Yb3+

Abstract

Near-infrared (NIR)-emitting phosphors with broadband absorption from ultraviolet to visible light have been considered significant spectral converter materials for solar cells. In this work, NIR phosphor Zn₃Ga₂GeO₈ (ZGGO):Cr³⁺,Yb³⁺ spinel solid solutions were synthesized using the classical high-temperature solid-state method. With an increase in the doping concentration of Cr³⁺ ions in ZGGO:Cr³⁺,Yb³⁺, a more distorted octahedron appeared around Cr³⁺ ions, which increased crystal field splitting. This process was accompanied with a broadening of NIR emission from Cr^{3+ 4}T₂ → ⁴A₂ transition and enlarged the overlap area between the absorption spectrum of Yb³⁺ and the emission spectrum of Cr³⁺, resulting in an efficient energy transfer between Cr³⁺ and Yb³⁺. In the case of high-concentration Cr³⁺ doping, the near-infrared luminescence intensity of Yb³⁺ was more than 8 times that of low-concentration doped Cr³⁺. Therefore, it is proposed that the Cr³⁺,Yb³⁺ co-doped ZGGO phosphor is a potential spectral convert materials for silicon-based solar cells and thereby improves photovoltaic conversion efficiency.