Blue and Orange Photoluminescence and Surface Band-Gap Narrowing in Lithium-Doped MgO Microcrystals

Abstract

Structure and properties of Li-doped MgO have been extensively studied during the past decades in view of the effect of aliovalent doping on the catalytic, optical absorption and magnetic properties. However, the photoluminescence (PL) properties of Li-doped MgO have not been systematically investigated previously. In this work, we prepared micrometer-sized Li-doped MgO crystals using solid-phase redox reaction between B2O3 and metals of Mg and Li under argon atmosphere. The resulting Li-doped MgO microcrystals exhibit blue (2.8 eV or 440 nm) and orange PL (2.1 eV or 580 nm) emissions under excitation with photons of energies of ∼5 and ∼3 eV, respectively. The blue PL is attributed to the bulk oxygen vacancies, or F-type centers, whose emission energy levels are modified by the Li ions incorporated into the MgO structure. On the other hand, the orange PL presumably results from the oxygen vacancies at the near surface regions where a substantial bandgap narrowing down to visible range of ∼3 eV occurs. It is also found that the photoexcited electrons generated by surface interband transition can be transferred to the surface emission states via thermal activation, resulting in temperature antiquenching of the orange PL emission. Hence, the present method provides a simple and effective way to prepare visible luminescent Li-doped MgO microcrystals with an intriguing effect of aliovalent doping both on the bulk and surface electronic structures.

Bioactivity Performance of Pure Mg after Plasma Electrolytic Oxidation in Silicate-Based Solutions

“…MgO nanostructures showed emission in the UV-Vis-NIR range [ 29 , 30 , 31 , 32 , 33 , 34 ]. The observed emission can be explained by structural defects [ 29 ].…”

“…The observed emission can be explained by structural defects [ 29 ]. PL peaks, observed in the range 380–520 nm, are associated with F/F+ centers (alkali ions/atoms) and oxygen vacancies [ 29 , 30 , 31 , 32 , 33 , 34 ]. The observed PL emission in the range of 600–800 nm is attributed to surface structural defects, such as oxygen vacancies and interstitials [ 29 , 30 , 31 , 32 , 33 ].…”

“…Mg PEO samples showed four characteristic emission peaks, centered at 360-380, 450, 500 and 660 nm. MgO nanostructures showed emission in the UV-Vis-NIR range [29][30][31][32][33][34]. The observed emission can be explained by structural defects [29].…”

Facile one-pot green synthesis of almond gum coated MgO nanoparticles for Biological applications

“…It is used in the various biomedical sectors and to treat many ailments such as antibacterial, anti-bio lm, anticancer, antiin ammatory, molecular diagnostics, and tissue engineering. Magnesium-based nanomaterials are involved in targeted drug delivery, antibiotics, and in vivo imaging purposes [9][10][11][12][13][14][15]. As mentioned before, magnesium nanoparticles as a killer particle to destroy speci cally targeted cells.…”

Synthesis, Properties, and Selected Technical Applications of Magnesium Oxide Nanoparticles: A Review

“…For this purpose, absorbance spectra and Tauc plots are used. The photoluminescence method (PL) [ 44 , 45 ] is also frequently used to determine the bandgap width.…”