The Influence of Mg Doping in α-Al2O3 Crystals Investigated with First-Principles Calculations and Experiment

The influence of Mg doping in α-Al2O3 crystals is investigated in this article by first-principles calculations and formation energies, density of states, and computed absorption spectra. Three models related to Mg2+ substituting for Al3+ doping structures were constructed, as well as spinel structure models with varying aluminum-magnesium ratios. The formation energy calculations confirmed the rationality of the MgAlVO model, which means that Mg substitutional doping incorporating oxygen vacancies is most likely to form in crystals. The combined action of magnesium and oxygen vacancies introduced new defect energy levels in the bandgap. The calculated absorption spectra of the MgAlVO and Mg-rich spinel structures exhibited various color centers. The experimental absorption spectra and thermoluminescence characteristics of α-Al2O3:Mg and alumina-magnesium (Al-Mg) spinel crystal samples were tested. The thermoluminescence peak of the Al-Mg spinel was significantly stronger than that of the α-Al2O3:Mg crystal. The consistency between the model-calculated absorption spectra and the experimental results confirmed the theoretical predictions. Based on the experimental and computational results, the influence of Mg2+ substitutional doping in α-Al2O3 and the impact of the locally Mg-rich spinel on the optical and radiation performance of α-Al2O3:Mg crystals are elucidated.