F+↔FCenter Conversions in Magnesium Oxide

Sol–gel synthesis of highly luminescent magnesium oxide nanocrystallites

“…The oxygen vacancies in MgO are usually produced by two methods, viz., irradiation with energetic particles such as neutrons, electrons, or ions, and thermo-chemical reduction (TCR) performed under very severe environmental conditions [10][11][12][13][14][15][16]. But, the thermal decomposition process of magnesium oxalate dihydrate can itself generate oxygen vacancies.…”

“…The nature of various F centres in MgO depends on the synthesis process, treatment conditions, etc. For example, neutron or ion irradiation generates F + centres, thermo-chemical reduction leads to neutral F centres, and electron-irradiation gives rise to both the F and F + centres [10][11][12][13][14][15][16]. If the concentration of F (or F + ) centres becomes high, aggregates/dimmers, i.e., FF, FF + , and F + F + type centres (termed as F 2 , F 2 + and F 2 2 + , centres, respectively) may possibly be formed as well.…”

Blue luminescence at room temperature in defective MgO films

“…Based on a broad number of theoretical and experimental studies on defects in MgO crystals, the 420, 440 and 530 nm bands can be assigned to F-type centers [20][21][22]. The emission feature at about 480 nm is ascribed to recombination processes resulting from the formation of higher-order vacancy complexes, probably associated to hydroxyl groups in a state of low coordination [23].…”

Photoconversion ofF-type centers in thermochemically reduced MgO single crystals

“…When a TCR sample is placed on a hot plate (Ͼ450 K͒, any F ϩ centers present become exclusively F centers. 7 Since these vacancies are produced nonstoichiometrically, there are no interstitials to annihilate the vacancies. Therefore the F centers are stable even at very high temperatures, ϳ1100 K. 6,8 However, the production of anion vacancies by TCR is normally also attended by the H Ϫ ion, 9 which is a proton trapped at a double-negative anion vacancy site and is therefore positively charged.…”