Gadolinium oxide Single crystals: Optical properties and radiation resistance

Gadolinium oxide (Gd2O3) is used in medical diagnostics as a contrast agent for ultrasound and magnetic resonance imaging, computed tomography, radiation therapy and gadolinium neutron capture for cancer treatment, and in biomedicine for cell labelling, fluorescence microscopy and spintronics.Gd2O3 also has promising applications as a protective and corrosion-resistant coating, a catalyst, a grain-growth inhibitor, and phase stabiliser, as well as in optical applications, X-ray imaging systems, sensors and nuclear engineering. Gd2O3 is also expected to be used in protective and corrosion-resistant coatings, catalysts, grain growth inhibitors, phase stabilisers, as well as optical applications, X-ray imaging systems, sensors and nuclear engineering. Therefore, in order to fully exploit its applications, it is important to have a good understanding of its properties.

Large-size high optical quality Gd2O3 single crystals were grown from solution at T = 1145 °C by Czochralski method. XRD analysis showed that the crystal structure is characterized by a single cubic phase (С-phase). Absorption spectra and luminescence properties of Gd2O3 doped with impurity Tb3+ ion were studied. The absorption spectrum is determined by electronic transitions in Gd3+ ion (spectral region of 245–315 nm) and interband electron transitions below 240 nm. Intraconfigurational radiative f-f transitions from 5D4 level in Tb3+ ion are clearly manifested upon both UV- and X-ray excitation. At the same time, 6PJ → 8S7/2 radiative transitions in Gd3+ ions are completely absent. This fact indicates high efficiency of nonradiative energy transfer from Gd3+ to Tb3+ ions. Thermo-luminescent spectroscopy shows the absence of charge carrier trapping centers, which proves the perfection of its crystal structure. The crystal under study shows high radiation resistance to high-energy (E = 10 MeV, D = 105 kGy) electron beam. However, the effects of irradiation appear only in the photoluminescence excitation spectra and thermally stimulated luminescence.

Structural motifs for diferent phases of Gadolinium oxide

Structural motifs for diferent phases of Gd2O3. a–d Hexagonal, monoclinic, cubic and tetragonal phases, respectively. The pink and red spheres indicate gadolinium (Gd) and oxygen (O) atoms, respectively.

At room temperature and atmospheric pressure, the C-phase Gd2O3 exhibits thermodynamically stable cubic bixbyite structure with space group Ia? 3. The conventional unit cell of the C-phase has one formula unit containing 32 Gd atoms and 48 O atoms. The A-phase having a hexagonal primitive unit cell follows the space group P? 3m1, the B-phase of Gd2O3 is monoclinic with space group C2/m and the tetragonal D-phase follows the space group P? 4 m2.

First-principles calculations based on density functional theory (DFT) were used to study the structural, elastic and mechanical properties of gadolinium oxide (Gd2O3) at the level of generalized gradient approximations in diferent polymorphic phases. All calculations were performed with the projectoraugmented wave method within the framework of DFT in cubic (bixbyite), hexagonal, monoclinic as well as tetragonal phases. The results of lattice constants and diferent elastic moduli with generalized gradient approximation are found to be reliable. This study also reveals that the bulk modulus for all the phases of Gd2O3 lies around 100 GPa suggesting that the considered phases are soft in nature and can simply be deposited as better quality thin flms, which is important for thin-flm based applications. Elastic properties such as bulk and shear elastic moduli, mechanical stability and elastic anisotropy were calculated that is not available in the literature. In this observation, Gd2O3 exhibited ductile nature and mechanically stable behavior in all polymorphic phases.

References:

[1] V.A. PUSTOVAROV . Gadolinium oxide single crystals: Optical properties and radiation resistance[J]. Optical Materials, 2023. DOI:10.1016/j.optmat.2023.113966.

[2] MAHABUL ISLAM  S. B  P Rajak. Ab initio calculation insights into the structural, elastic and mechanical properties of high-k dielectric gadolinium oxide (Gd2O3)[J]. Applied Physics A, 2019. DOI:10.1007/s00339-019-3060-4.