Assignment of Photoluminescence Spectra of MgO Powders: TD-DFT Cluster Calculations Combined to Experiments. Part I: Structure Effects on Dehydroxylated Surfaces

Abstract

Photoluminescence excitation spectra of dehydroxylated MgO powders are assigned from a combined theoretical and experimental approach. Experimentally, a set of five species is identified, among which are two new species, by recording the spectra with enhanced resolution and at 77 K so as to minimize energy transfer along the surface. Performed on various clusters modeling terraces, edges, monatomic steps, corners, kinks, and divacancies, TD-DFT calculations show that the excitation energy depends not only on the coordination of surface ions, but also on the local topology (kinks versus corners for example). This, together with the fact that a single defect can be excited at several wavelengths, explains the complexity of the experimental spectra and the difficulty encountered so far for their assignment. Several groups of calculated excitation energies can be identified which enable to rationalize the assignment of the experimental spectra.

Optical and fluorescence properties of MgO nanoparticles in micellar solution of hydroxyethyl laurdimonium chloride

“…It has been shown that the cubic-MgO is a wide-band gap energy material and normally does not demonstrate the fluorescence characteristic [13,25,7]. In the MgO crystalline structure, some structural defects are present, such as magnesium vacancies (3 and 4-coordinated Mg 2+ ) and oxygen vacancies (3 and 4-coordinated O 2− ) [10,26]. There are three active sites or surface anions (oxygen, O 2− ) present; (i) 3-coordinated at the corner (ii) 4-coordinated at edges, and (iii) 5-coordinated at the planar site in the MgO nanoparticles, which belong to surface defects at the stepped and kinked surfaces [27][28][29][30].…”

Effects of surface stability on the morphological transformation of metals and metal oxides as investigated by first-principles calculations

“…The crystal habits are principally determined by relative energies of the exposed planes, and entropy terms normally do not affect this ordering [68]. The entropic and pV contributions to the free energies change slightly throughout the condensedphase species and in this type of calculation the entropic term is neglected [68][69][70][71][72][73]. Therefore, the difference between the Gibbs free energies can be approximated by the difference between the total energies from first-principles calculations [74][75][76].…”

Insights into the Geometry, Stability and Vibrational Properties of OH Groups on γ-Al2O3, TiO2-Anatase and MgO from DFT Calculations

“…c-Al 2 O 3 , [18,19] TiO 2 -anatase [20,21] and MgO [22] have recently been studied at the same level of theory (Density Functional Theory, periodic boundary conditions and PW91 functional). The models proposed have been extensively compared to experiments (TPD, [22,23] IR, [19,[24][25][26][27] 1 H NMR, [28] photoluminescence [29,30]) and used to describe the interaction of the support with active phases (metals, [12,13,31,32] sulfides, [32][33][34] organometallic complexes [35]). …”