Luminescence Properties\nof Bi<sup>3+</sup>-Doped Gd<sub>2</sub>O<sub>3</sub> Phosphor under\nUV and X‑ray Excitation

X-ray excited luminescence in scintillators plays a crucial\nrole\nin applications ranging from medical diagnostics to industrial quality\ninspection and scientific research. This study explores the potential\nof Bi<sup>3+</sup>-doped Gd<sub>2</sub>O<sub>3</sub> phosphors as\nnext-generation scintillators, leveraging their broad-spectrum emission\ncharacteristics to achieve higher light yields. We synthesized Gd<sub>2</sub>O<sub>3</sub>:Bi<sup>3+</sup> phosphors in two crystalline\nphasescubic and monoclinicusing a high-temperature\nsolid-phase method. These phosphors demonstrate varied applications,\nfrom backlighting displays to X-ray imaging of opaque and biological\nsamples. Under UV light excitation, each phase exhibits distinct luminescence\nproperties due to different Bi<sup>3+</sup> occupancy environments.\nThe monoclinic phase, excited at λ<sub>ex</sub> = 370 nm, showed\nstronger luminescence and a broader emission peak (fwhm = 70 nm) with\na higher photoluminescence quantum yield (67.94%), compared to the\ncubic phase, which under optimal conditions (λ<sub>ex</sub> =\n377 nm) exhibited narrower peaks (fwhm = 40 nm) and a lower yield\n(44.41%). Notably, under X-ray excitation, the cubic phase outperformed\nwith a higher light yield (48,900 photons/MeV) and lower detection\nlimits (380 nGy·s<sup>–1</sup> at λ<sub>em</sub> = 430 nm and 285 nGy·s<sup>–1</sup> at λ<sub>em</sub> = 520 nm). Both phosphors were also embedded in PMMA to create thin\nfilms for X-ray imaging, achieving high-resolution outputs (14 lp·mm<sup>–1</sup>).