Enabling Yb³⁺ Luminescence with Visible Light Response in Mg₂GeO₄ via Energy Transfer

The growing demand for spectroscopy applications in the areas of bioimaging, food quality analysis, and temperature sensing has led to extensive research on infrared light sources. It is crucial for the design of cost-effective and high-performance systems that phosphors possess the ability to absorb blue light from commercial LEDs and convert the excitation energy to long-wavelength infrared luminescence. In this work, we obtained Yb³⁺ luminescence with visible light response by utilizing the energy transfer from Cr³⁺ to Yb³⁺ in Mg₂GeO₄. After the introduction of Yb³⁺, intense NIR luminescence peaking at 974 nm can be achieved with an increasing intensity. The local structure analysis was performed to investigate the preferential occupation of Yb³⁺ ions and the energy transfer process in Mg₂GeO₄. Considering the properties of thermally coupled anti-Stokes and Stokes emissions of Yb³⁺ and the sensitive variation of the emission intensity, the potential application of Mg₂GeO₄:Cr³⁺, Yb³⁺ as thermometers was demonstrated.