Eu ^{3 <b>+</b>} complex as an Efficient Luminescent Sensitizer for NIR-Emitting Core–Shell Zn _x Mg _y SnO ₄ :Cr ^{3 <b>+</b>} Persistent Luminescence Materials

This work presents the development of core–shell ZnxMgySnO4:Cr3+ (40 and 80% Mg) persistent luminescent (PersL) materials prepared by the ceramic method and decorated with the [Eu(tta)3(H2O)2] complex via microwave-assisted silanization, with promising optical properties in the near-infrared (NIR) range. The crystal structure of the prepared materials showed overlapping Mg2SnO4 and Zn2SnO4 patterns, along with SnO2, with increasing Mg content. FESEM and TEM microscopy revealed polycrystalline particles with well-defined surfaces and a silica shell in the 5–10 nm range. The optical properties were investigated by UV–vis and synchrotron spectroscopies (VUV, XANES-XEOL, and XRF). The persistent luminescent materials exhibit a noticeable increase in band gap energy with higher Mg content, intense, broadband NIR emission centered at 780 nm from the Cr3+ ion in a weak crystal-field environment, as well as longer PersL decay time with a higher Mg/Zn ratio. Core–shell materials decorated with the Eu3+-complex indicate energy transfer to the Cr3+ ion, resulting in NIR luminescence sensitization by UV and X-ray excitation. Therefore, we demonstrate an effective strategy to sensitize NIR emission by utilizing a highly efficient Eu3+ complex in core–shell persistent luminescent materials, which exhibit notable structural and optical properties and hold promise for optical imaging and photonic applications.