Surface exciton emission of MgO crystals

• Published in: Journal of physics. D, Applied physics Vol. 46; no. 36; pp. 365501 - 1-6
• Main Authors: Kuang, Wen-Jian, Li, Qing, Chen, Yu-Xiang, Hu, Kai, Wang, Ning-Hui, Xing, Fang-Li, Yan, Qun, Sun, Shuai-Shuai, Huang, Yan, Tao, Ye, Tolner, Harm
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 11.09.2013; Institute of Physics
• Subjects: Broadband; Collective excitations (including excitons, polarons, plasmons and other charge-density excitations); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Crystals; Diffusion in nanoscale solids; Diffusion in solids; Doping; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Emission; Emittance; Exact sciences and technology; Excitation; Magnesium oxide; Materials science; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Physics; Surface and interface electron states; Terraces; Transport properties of condensed matter (nonelectronic); Magnesium oxide; Doping; Fluorine additions; Surface excitons; Energy gap; Ultraviolet radiation; Impurities; Wide band; Calcium nitride; Visible radiation; Scandium; Silicon; Diffusion; Extreme ultraviolet radiation; Nanostructured materials; Surface energy; Synchrotron radiation
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/46/36/365501

MgO crystals have been exposed to vacuum ultraviolet (VUV) radiation from a synchrotron, with energies up to 9 eV, and the emitted light, at wavelengths above 200 nm, was observed. It is concluded that bulk excitons, play an important role in the diffusion of energy inside MgO crystals, resulting in 5.85 eV (212 nm) emission from the MgO terraces of large (0.2-2 µm) MgO : F crystals. In the case of aliovalent impurity doping, then the bulk exciton energy is also transferred to the Vk centres and 5.3 eV (235 nm) light is emitted. Both fluorine and silicon doping appear to promote UV surface emission, acting similarly to an ns2 ion inside MgO, while strong scandium doping is killing the surface emission completely. The 212 nm surface UV emission and the 235 nm bulk UV emission can be excited only at the bandgap edge. Broadband visible light, centred around 400 nm, is also emitted. Contrary to the UV emission, this is not generated when excited at the bandgap edge; instead, we find that it is only excited at sub-bandgap energies, with a maximum at the 5C surface excitation energy of 5.71 eV (217 nm) for the MgO terraces.