Cr3+ IONS IN HYDROGENATED AND PROTON EXCHANGED LiNbO3 CRYSTALS

Agata Kaminska 2Luis Arizmendi 1Andrzej Suchocki 

1. Universidad Autonoma de Madrid (UAM), Cantoblanco, Madrid 28034, Spain
2. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland

Abstract

Lithium niobate (LN) crystals remain of the interest for applications as well as for fundamental studies. The Cr3+ ions turned out to be a very good probe of that structure since they substitute for both Li or Nb ions in LN host. Several studies with use of EPR and ENDOR techniques have been performed that helped to identify several Cr3+ centers both in Li (CrLi) and Nb (CrNb) sites. Also high-pressure low-temperature optical spectroscopy was very successful in identification of optically active Cr3+ centers. High-pressure application transforms low-strength crystal field of Cr3+ centers into high-strength crystal field, what increases spectral resolution of the measurements and allows for their easier characterization.
Doping of lithium niobate with trivalent ions requires some charge compensation. Recently on the basis of EPR and ENDOR it has been suggested that interstitial hydrogen ions or additional Li+ ions in structural vacancies in LiNbO3 can provide required charge compensation for chromium ions in niobium sites (CrNb). It is known that LN can accommodate large amount of OH- molecules and their concentration can be controlled either by annealing crystals in water vapor or by proton-exchange in relatively thin surface layer of the crystal.
We studied influence of both annealing in water vapor and proton exchange on high-pressure low-temperature luminescence spectra of near stoichiometric LN:Cr,MgO crystals, containing both CrLi and CrNb centers by using diamond-anvil cell. The observed changes of the spectra of Cr3+ ions are associated with the larger inhomogeneous broadening and increase of of the splitting of the 2E level in one of the CrLi center, so called center γ. This shows that neither increase of hydrogen concentration in LN by almost two orders of magnitude (from 1018 to almost 1020 cm-3) nor proton-exchange procedure do not create any new optically active Cr3+ centers in those crystals.

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Presentation: oral at E-MRS Fall Meeting 2003, Symposium A, by Agata Kamińska
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-27 09:30
Revised:   2009-06-08 12:55
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