Color Origins in Langatate Crystals

  • Maroua Allani FEMTO-ST Institute
  • Narjès Batis INSAT, Université de Carthage, BP 676, 1080 Tunis cedex, Tunisia
  • Abdeldjelil Nehari ILM Institute, UCBL, 69000 Lyon, France
  • Hugues Cabane Cristal Innov, 73800 Sainte-Hélène du Lac, France
  • Kheirreddine Lebbou ILM Institute, UCBL, 69000 Lyon, France
  • Christophe Pecheyran LCABIE - IPREM –Université de Pau - 64053 Pau Cedex 9, France
  • Corine Reibel Institut Charles Gerhard, Université de Montpellier, 34000 Montpellier, France
  • Jean-Jacques Boy FEMTO-ST Institute, UFC, CNRS, ENSMM, UTBM, 25000 Besançon, France

Abstract

Langatate La3Ga5.5Ta0.5O14 is piezoelectric crystal from langasite family, commonly grown by Czochralski method from Ir crucible. Langatate crystals of different colors (colorless, orange, green) have been studied by optical spectroscopy in UV-Visible (200 – 800 nm) and IR (7000 – 1000 cm-1) ranges. Furthermore, the effects of irradiation by ultraviolet laser source (λ=266 nm) and post-growth annealing in N2+O2 atmosphere have been investigated. The yellow-orange is mainly due to an absorption centered in the ultraviolet that extends into the blue of the visible spectrum (250-500 nm). The IR optical absorption spectra of Langatate crystals exhibit an absorption band at 5370 cm-1. It seems linked to a point defect responsible for color. The intensity of the absorption band at 3430 cm-1 increases after annealing in oxygen containing atmosphere. We have discussed phenomenon that can occur simultaneously in langatate crystals and produce very similar colors which are related to structural defects. First, metal ions impurities (as Iron, Titanium…), whose presence is previously confirmed by femtosecond laser ablation coupled with ICP-MS spectroscopy, can contribute to langatate color. Second, ultraviolet absorption leads us to think about charge transfer phenomenon such as O2- → Fe3+ and/or Fe3+-Fe3+ pair transitions. Third, the irradiation by ultraviolet (λ=266 nm) laser source locally color the langatate sample by the creation of color centers. Origins of color centers, particularly those related to oxygen vacancies, ( , 2e′)x, are discussed. And, finally, point defects changes the band gap of langatate, leading to extend the absorption to visible light regions.

Keywords: color, color centers, charge transfer, ESR spectrum, fs LA-ICP-MS coupling, impurities, langasite family crystals, optical spectrometry.

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Published
2017-06-30
How to Cite
[1]
M. Allani, “Color Origins in Langatate Crystals”, Int. Ann. Sci., vol. 2, no. 1, pp. 12-19, Jun. 2017.
Section
Research Article