A recent study has made a breakthrough in the understanding of upconversion luminescent materials, particularly in revealing the energy back transfer (EBT) mechanism between Yb3+ and Er3+ ions. Researchers utilized Er3+-doped Yb3+-self-activated NaYb(MoO4)2 phosphor and crystal, as well as Yb3+/Er3+ codoped NaBi(MoO4)2 crystal as research subjects to investigate the effects of factors such as excitation power density and Yb3+ ion concentration on the EBT process. Through the study of various samples in different states (phosphors and crystals) and different doping conditions, they found that at high power densities, the EBT process induces a transition from green to yellow luminescence in self-activated samples, while the NaBi(MoO4)2 crystal maintains bright green luminescence within the measured power density range. This finding is very important because it provides a deeper understanding of the EBT mechanism, and previous studies have not fully explored the EBT mechanism. They revealed the relationship between the EBT mechanism and factors such as the excitation power density, Yb3+ concentration and the structural order of the sample, which provided a theoretical basis and optimization direction for optical temperature measurement.
The research was led by Prof. Shoujun Ding and his team from Anhui University of Technology. Using a combination of high-temperature solid-state methods and the Czochralski method, the team successfully synthesized the phosphor and crystal samples. They employed advanced techniques such as X-ray diffraction, UV–Vis–IR absorption spectroscopy, and upconversion emission spectroscopy to analyze the samples. The research paper includes high-quality images of the synthesized samples and their luminescence under different power densities. These visual aids effectively demonstrate the differences in luminescence between the phosphor and crystal samples, highlighting the impact of the EBT process. The work entitled " Effect of energy back transfer from Er3+ to Yb3+ ions on the upconversion luminescence of Er:NaYb(MoO4)2 and Yb,Er:NaBi(MoO4)2 " was published on Frontiers of Optoelectronics (published on May 15, 2025).
