Tunable Broadband NIR-II Emission via Cr⁴⁺-Er³⁺ Energy Transfer in CaMgGeO₄:Cr⁴⁺,Er³⁺ Phosphors for Nondestructive Analysis

Although there have been numerous reports on broadband near-infrared (NIR) emitting phosphors, their emissions are mainly concentrated in the range of 700-1000 nm (NIR-I). Herein, we successfully synthesized a broadband near-infrared phosphor CaMgGeO₄:Cr⁴⁺(CMG:Cr⁴⁺) with an emission in the range of 1000-1600 nm (NIR-II). The introduction of Er³⁺ ions into CMG:Cr⁴⁺ resulted in a wider near-infrared emission phosphor CaMgGeO₄:Cr⁴⁺,Er³⁺ (fwhm = 361 nm), compensating for the luminescence of 1500-1600 nm. More importantly, an energy transfer from Cr⁴⁺ to Er³⁺ ions has been discovered. Furthermore, a NIR pc-LED was fabricated by combining the CMG:Cr⁴⁺,Er³⁺ phosphor with a 590 nm chip. The changes in intensity and profile of the transmission spectra of light passing through different liquids reveal its potential application in organic compound recognition. This work opens a direction for the development of NIR-II phosphors.