Erbium-Doped Lu2O3-MgO and Sc2O3-MgO IR-Transparent Composite Ceramics

Novel IR-transparent ceramics of erbium-doped Lu₂O₃-MgO and Sc₂O₃-MgO composites have been successfully obtained using a combination of glycine-nitrate self-propagating high-temperature synthesis and vacuum hot-pressing methods. Composites have densities greater than 99.5% of those calculated by X-ray diffraction and consist of uniformly distributed submicron grains of magnesium and rare earth oxides. The transmittances of 1.5 mm thick composites are as high as 84.5% and 78.9% at ~5 µm for Er:Lu₂O₃-MgO and Er:Sc₂O₃-MgO, respectively. Both composites are favorable matrices for doping with erbium ions, which exhibit intense luminescence in the visible, near, and mid-IR under relevant excitation. The position of the luminescence bands is similar to Er:Lu₂O₃ and Er:Sc₂O₃ ceramics; the lifetimes of the ⁴I_13/2 state are 8.85 ± 0.1 ms and 5.7 ± 0.2 ms for 3%Er:Lu₂O₃-MgO and 3%Er:Sc₂O₃-MgO, respectively.

General embedded cluster protocol for accurate modeling of oxygen vacancies in metal-oxides

The O vacancy (Ov) formation energy, EOv, is an important property of a metal-oxide, governing its performance in applications such as fuel cells or heterogeneous catalysis. These defects are routinely studied with density functional theory (DFT). However, it is well-recognized that standard DFT formulations (e.g., the generalized gradient approximation) are insufficient for modeling the Ov, requiring higher levels of theory. The embedded cluster method offers a promising approach to compute EOv accurately, giving access to all electronic structure methods. Central to this approach is the construction of quantum(-mechanically treated) clusters placed within suitable embedding environments. Unfortunately, current approaches to constructing the quantum clusters either require large system sizes, preventing application of high-level methods, or require significant manual input, preventing investigations of multiple systems simultaneously. In this work, we present a systematic and general quantum cluster design protocol that can determine small converged quantum clusters for studying the Ov in metal-oxides with accurate methods, such as local coupled cluster with single, double, and perturbative triple excitations. We apply this protocol to study the Ov in the bulk and surface planes of rutile TiO2 and rock salt MgO, producing the first accurate and well-converged determinations of EOv with this method. These reference values are used to benchmark exchange–correlation functionals in DFT, and we find that all the studied functionals underestimate EOv, with the average error decreasing along the rungs of Jacob’s ladder. This protocol is automatable for high-throughput calculations and can be generalized to study other point defects or adsorbates.

Inferring Relative Dose-dependent Color Center Populations in Proton Irradiated Thoria Single Crystals using Optical Spectroscopy

We have utilized photoluminescence spectroscopy and optical ellipsometry to characterize the dose-dependence of the photoluminescence emission intensity and changes in optical absorption of thoria single crystals subject to irradiation with...

A periodic equation-of-motion coupled-cluster implementation applied to F-centers in alkaline earth oxides

We present an implementation of the equation of motion coupled-cluster singles and doubles (EOM-CCSD) theory using periodic boundary conditions and a plane wave basis set. Our implementation of EOM-CCSD theory is applied to study F-centers in alkaline earth oxides employing a periodic supercell approach. The convergence of the calculated electronic excitation energies for neutral color centers in MgO, CaO, and SrO crystals with respect to the orbital basis set and system size is explored. We discuss extrapolation techniques that approximate excitation energies in the complete basis set limit and reduce finite size errors. Our findings demonstrate that EOM-CCSD theory can predict optical absorption energies of F-centers in good agreement with experiment. Furthermore, we discuss calculated emission energies corresponding to the decay from triplet to singlet states responsible for the photoluminescence properties. Our findings are compared to experimental and theoretical results available in the literature.

Pressure-induced photoluminescence of MgO

It is reported in this paper that pressure can promote strong photoluminescence (PL) in MgO. The PL measurements of MgO indicate that it has no obvious luminescence at pressures lower than 13 GPa. PL starts to appear upon further compression and reaches a maximum intensity at about 35 GPa. The center of the emission band shows a red shift at lower pressures and turns to a blue shift as pressure exceeds 25 GPa. The PL is preserved upon complete decompression. The defects and micro-strain due to the plastic deformation of MgO are likely responsible for the origin of the luminescence.

Defects induced changes in the electronic structures of MgO and their correlation with the optical properties: a special case of electron–hole recombination from the conduction band

Defect induced tunable emission in MgO is investigated using photoluminescence and DFT calculations.

First-principles optical spectra for F centers in MgO

The study of the oxygen vacancy (F center) in MgO has been aggravated by the fact that the positively charged and the neutral vacancy (F+ and F0, respectively) absorb at practically identical energies. Here we apply many-body perturbation theory in the G0W0 approximation and the Bethe-Salpeter approach to calculate the optical absorption and emission spectrum of the oxygen vacancy in all three charge states. We observe unprecedented agreement between the calculated and the experimental optical absorption spectra for the F0 and F+ center. Our calculations reveal that not only the absorption but also the emission spectra of different charge states peak at nearly the same energy, which leads to a reinterpretation of the F center's optical properties.

Hartree-Fock Cluster Computations for Ionic Crystals

The ICECAP code is applied to charged and uncharged color centers in alkali halides and alkaline-earth oxides, to test the usefulness of complete-cation pseudopotentials for reproducing the cluster boundary conditions. The physical model includes consistency up to electrostatic octupole order between the Hartree-Fock cluster and the surrounding infinite shell-model lattice. The total energy of the system is determined variationally, including distortion and polarization of the cluster and lattice, and LCAO-MO gaussian-localized cluster wave functions. Electronic states with the lattice unrelaxed are also analysed, yielding color-center optical transition energies. Furthermore, consistency between quantum (cluster) and classical (shell-model) descriptions of the perfect lattice is tested.

On refractory oxide crystals for continuous-wave tunable lasers

It is demonstrated that trapped-hole centers can be a detriment to continuous-wave tunable-laser action in irradiated oxide crystals operating in or near the visible region. Thermochemically reduced oxide crystals appear to be more promising.

Tunable visible lasers using F(+) centers in oxides

Continuous-wave laser action using F(+) centers in CaO crystals is reported in the blue range of the visible spectrum. These centers may be pumped by using either Ar(+) or N(2) laser lines. The laser is tunable in the range 357-420 nm with an output power of approximately 15 mW at the band center for an input power of 100 mW.