Luminescence Tuning of NIR Luminescence Nanophosphor Bi³⁺/Yb³⁺-Doped RE₂MoO₆ (RE = Gd, Y, and Lu) and Gd₂Mo_1–<i>x</i>W_<i>x</i>O₆

Near-infrared nanophosphors have attracted attention due to their wide application fields, including component analysis, bioimaging, and spectral converters of sunlight for crystalline silicon solar cells (c-Si). Yb3+ ions exhibit near-infrared (NIR) luminescence at around 1000 nm, which is consistent with the first biological window and the maximum responsivity range of c-Si. Therefore, we focused on and successfully synthesized Bi3+/Yb3+-doped NIR luminescence nanophosphors, RE2MoO6:Bi3+,Yb3+ (RE=Gd, Y, and Lu) and Gd2Mo1–xWxO6:Bi3+,Yb3+ (x = 0–0.5), utilizing a solvothermal reaction process. All samples exhibit NIR luminescence of Yb3+ ions under ultra-violet (UV) light excitation and broadband excitation due to the charge transfer transition between the O 2p/Bi 6s and Mo 4d or W 5d orbitals, indicated by their optical properties of photoluminescence (PL), PL excitation (PLE), and reflectance spectra. Furthermore, to evaluate the contribution of the Gd2MoO6:Bi,Yb (GMO:Bi,Yb) nanophosphor to the conversion efficiency of c-Si, a phosphor-converted film was made using dimethylpolysiloxane (PDMS) and the GMO:Bi,Yb nanophosphor. The results showed that the conversion efficiency of c-Si with the PDMS/GMO:Bi,Yb film is higher than that of c-Si with the PDMS-only film. Based on these results, the utilization of down-shifting nanophosphors is able to enhance the conversion efficiency of c-Si, which could be beneficial in addressing future energy challenges.