Abstract
The investigation of electrical properties in alexandrite (BeAl2O4:Cr3+) in synthetic and natural forms is presented in this paper. Alexandrite is a rare and precious mineral that changes color according to the light incident on it. In the synthetic form, it is used technologically as an active laser medium. The electrical characterization was obtained using the Thermally Stimulated Depolarization Current (TSDC) technique, an interesting tool to study the behavior of impurities in insulators. Alexandrite presented the electric dipole relaxation phenomenon, both in natural and in synthetic samples. It was possible to observe TSDC bands for the synthetic sample at around 170 K, and at around 175 K for the natural sample. Besides, photo-induced TSDC measurements were performed through the excitement of the samples by using a continuous wave argon laser. In addition, photoluminescence measurements were performed to verify in advance whether the laser light would be absorbed by the sample, and in order to complement the photo-induced TSDC measurements analysis. The results of photo-induced TSDC experiments have contributed to the understanding of the TSDC bands behavior: the results obtained with the technique suggest that there is an effective participation of Cr3+ ions in the formation of TSDC bands because they were more intense when the sample was exposed to the argon laser beam.
Highlights
Alexandrite is a variety of chrysoberyl crystal that contains chromium in its structure and presents the following chemical composition: BeAl2O4:Cr3+ [1] [2]
The results of photo-induced Thermally Stimulated Depolarization Current (TSDC) experiments have contributed to the understanding of the TSDC bands behavior: the results obtained with the technique suggest that there is an effective participation of Cr3+ ions in the formation of TSDC bands because they were more intense when the sample was exposed to the argon laser beam
According to Weber et al [17], based on chemical and geometric arguments, it is assumed that, in alexandrite originated from Russia, the Fe3+ ion replaces Al in octahedral sites in the structure once the tetrahedron Be site is too small for such replacement
Summary
Alexandrite is a variety of chrysoberyl crystal that contains chromium in its structure and presents the following chemical composition: BeAl2O4:Cr3+ [1] [2]. The technological importance of alexandrite has increased after 1974, when it was possible to use it in synthetic form as an active laser medium, with superior characteristics when compared to other types of media, with emission in the range between 700 and 800 nm [4]. The first scientists who suggested the possibility of application of synthetic alexandrite as laser crystals were Farrel in 1963 [5], but they were not successful in obtaining it in practice [6]. Bukin et al first reported the alexandrite laser in 1978 [7]. The Q-switched alexandrite laser operates in the range of 755 nm, near infrared emission spectrum. There are many recent works showing applications of the alexandrite laser in medicine as in the treatment of facial and labial lentigines associated with Peutz-Jeghers syndrome [9], café au lait macules [10], seborrheic keratoses [11], hirsutism [12], trichostasis spinulosa [13] and other applications such as hair removal [14] and tattoos removal [15]
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