Spectroscopy and X-ray Storage Capability of Rare-Earth Ions Doped and Undoped BaLiF3

Abstract

Storage phosphors have found widespread applications in dosimetry and computed radiography. To date, BaFBr(I):Eu2+ is the most commercially successful phosphor used in computed radiography. Due to their limited signal to noise ratio and erasure of stored information, investigations of alternative phosphor materials are crucial and BaLiF3 has emerged as a potential candidate. This thesis focuses on a thorough understanding of the luminescence phenomena and X-ray storage capability of single- doped (BaLiF3:Eu3+, BaLiF3:Sm3+ and BaLiF3:Tm3+), co-doped (BaLiF3:Yb3+, Er3+), and undoped BaLiF3. The doped and undoped BaLiF3 powder were prepared by ball milling and characterized using powder X-ray diffraction, transmission and scanning electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Their optical properties were characterized by photoluminescence, upconversion luminescence and photoluminescence excitation spectroscopy in external magnetic field (9 T). Photoluminescence properties of nanocrystalline BaLiF3:Eu3+, BaLiF3:Sm3+ and BaLiF3:Tm3+ before and after X-irradiation was studied to quantify their X-ray storage capability of such host-activator systems. It is demonstrated that BaLiF3 is a potential host which can enable luminescence within a broad optical range (UV–infrared) depending on the activator. In addition, upconversion luminescence in BaLiF3:Yb3+, Er3+ was investigated and shown to increase by 2 orders of magnitude upon treatment by annealing at higher temperatures. Furthermore, the reduction of Er3+ upconversion luminescence as well as Yb3+ and Er3+ photoluminescence in BaLiF3:Yb3+, Er3+ as a function of increasing X-ray doses were explored in detail. It is demonstrated that Yb3+ and Er3+ co-doped BaLiF3 exhibits desirable sensitivity to X-ray radiation. 2D X-ray images were recorded based on the observed upconversion luminescence which demonstrated their potential for X-ray imaging along with dosimetry. Finally, a F3+ colour centre is reported in undoped BaLiF3 upon annealing, which display a zero-phonon line at 764.8 nm. The zero-phonon line exhibited Zeeman effects in large magnetic fields due to a triplet ground state. This is the first observation of singlet to triplet luminescence of colour centre. The photoluminescence properties and X-ray storage capability of the F3+ centre was rigorously explored. Significantly, this thesis advances the understanding of luminescent properties of activated and pure BaLiF3 and sheds light on the utilization of these nanocrystals for practical implementations.