A NaBiF4:Gd/Tb nanoscintillator for high-resolution X-ray imaging

Abstract

Lanthanide doped fluoride nanoscintillators have received tremendous attention due to their high photochemical stability and tunable X-ray excited optical luminescence compared to traditional inorganic scintillators. Advancement in this field requires design strategies for the development of nanoscintillators that offer tailorable excitation dynamics through nanostructuring, thus enabling high luminescence in a suitable host. However, selection of an appropriate host matrix with low phonon energy and a nanoarchitecture that mitigates surface quenching due to the large surface-to-volume ratio of nanoparticles is still a challenge. Herein, we introduce NaBiF₄:Gd,Tb (NBF) nanoparticles as highly efficient nanoscintillators with reduced afterglow to minimize interference in radioimaging, which utilizes the high X-ray attenuation coefficient of bismuth (5.74 cm² g⁻¹ at about 100 keV). The host NaBiF₄ has a high refractive index and low phonon energy, which reduces the multiphonon non-radiative relaxation rates and enhances the radiative emission probability, thus yielding a long-life time for luminescence. Furthermore, by varying the composition of the nanoparticles and the relative concentrations of Gd and Tb, luminescence at multiple wavelengths in changing relative intensities can be achieved to enable multiplexed imaging. We show that NaBiF₄:Gd/Tb can be easily synthesized using the co-precipitation method at room temperature within 1 min. Furthermore, we succeeded in fabricating organic–inorganic nanocomposite self-standing films of NaBiF₄:Gd,Tb in high loading, uniformly dispersed in poly(methyl methacrylate) (PMMA) polymer. Their application in radiography is demonstrated by recording X-ray images using a commercially available charge-coupled device camera. We attained a resolution comparable to the non-flexible commercial CsI (TI) scintillator and significantly superior to the commercial Gd₂O₂S:Tb, GOS:Tb scintillators commonly used for screens.