Luminescence of Free and Relaxed Excitons in MgO

Abstract

The vacuum ultraviolet luminescence of pure and doped MgO crystals excited by 10 keV electrons is studied in the temperature region 80 to 450 K. At 80 K the narrow edge luminescence band at, 7.65 eV due t o radiative decay of free excitons dominates in the emission spectrum of undoped crystals. At thermal quenching of this luminescence with a n activation energy of (0.037 5 0.005) eV, another luminescence band with maximum a t 6.9 eV increases. The activation energy of this increase is (0.039 & 0.005) eV. No relation of the 6.9 eV luminescence band with the presence of impurities and defects could be established and it is suggested to be due to radiative decay of relaxed (self-trapped) excitons. MCCJIeAOBaHa BaKyyMHaR yJIbTpa#MOJIeTOBaH

Low‐temperature (4–295 K) thermoluminescence of pure and Ca‐doped MgO single crystals

“…The MgO and MgO:Ca crystals were grown in a carbon arc furnace with two spectrographic-grade graphite electrodes. The stainless-steel furnace reactor was water-cooled, and the mixed and pressed MgO-CaCO 3 powder was melted during 1 h, using an arc current of up to 300 A and voltage 70 V. In the course of cooling, crystals of up to 15 × 15 × 10 mm 3 were formed. The crystals were relatively fragile and hard to cleave.…”

“…According to one point of view, it arises at the radiative decay of relaxed free excitons [3], according to another [4] -at the decay of small radius excitons bound on a Ca 2+ defect. The last standpoint is supported by the observation that the 6.8 eV luminescence is the strongest in the MgO crystals intentionally doped with Ca.…”

Trapped-hole centers in MgO single crystals

“…Проблема автолокализации дырок в MgO изучается в течение длительного времени. В работе [18] люминес-центная полоса при 6.9 eV в монокристаллах MgO была интерпретирована как люминесценция автолокализован-ных или по крайней мере релаксированных экситонов. С другой стороны, согласно теоретическим расчетам, дырки не могут автолокализоваться в объеме MgO, но процесс автолокализации возможен в менее упорядочен-ных местах (углы, уступы и т.…”

“…Для под-тверждения этого вывода, противоречащего приписыва-нию свечения при ∼ 6.9 eV в номинально чистых мо-нокристаллах MgO автолокализованным экситонам [18], в нашей лаборатории были проведены дополнительные исследования кристаллов MgO : Ca (∼ 200 ppm). Кри-сталл был сначала выращен из исходных компонентов высокого уровня чистоты с применением разновидности метода дуговой плавки, а затем наиболее чистая часть полученного кристалла была использована в качестве сырья для рекристаллизации.…”

49.4: Photon and Electron Excitation Characteristics of MgO Submicron Crystals Made From Precursors

“…We also assume that excitons at 7.6eV, created by the 147nm lamp, or by high energy electrons, are moving through the crystals, until they meet one of these or other defects, resulting in either luminescence or the emission of exo-electrons. [10][11][12][13][14].…”