Comparative analysis of the Cr³⁺ centre spectroscopic properties in LiNbO₃ crystals from congruent to nearly stoichiometric compositions

¹ Laboratoire Matériaux Optiques, Photonique et Systèmes (CNRS-FRE 2304) , CLOES, Université de Metz et Supelec, 2 rue Belin, 57070 Metz Cedex 3, France
² Physico Chimie des Matériaux Luminescents, LPCML, Université Claude Bernard Lyon 1 (UMR 5620 CNRS) , Bât. A. Kastler, 10 rue Ampère, 69622 Villeurbanne Cedex, France

Corresponding author: georges.boulon@pcml.univ-lyon1.fr

Received: 18 December 2001
Revised: 11 June 2002
Accepted: 13 June 2002
Published online: 1 October 2002

Abstract

The properties of Cr³⁺ in LiNbO₃ single crystals have been investigated by means of several experiments including the recordings of absorption and high resolution laser spectroscopy spectra with dye-laser excitation spectra, emission spectra and fluorescence decays under laser selective pumping. Measurements performed on crystals with composition varying between congruent and close to stoichiometry enabled new features to be revealed which lead us to re-interpret the optical spectra of chromium-doped LN. Three chromium centres are sufficient to explain the main optical features. The main chromium centre labelled γ, giving rise to the broad absorption and emission bands, corresponds to the low-crystal field scheme where the ⁴T₂ level is lower than ²E. The two other chromium centres α and β yield sharp lines in emission and correspond to the high-crystal field scheme. Their dependencies on both the chromium concentration and the composition were studied using emission spectroscopy at low temperature. The main centre γ seems slightly affected by chromium concentration or composition change. The centres α and β are shown to be strongly connected to the presence in their surrounding of intrinsic defects related to the crystal non-stoichiometry. From their behaviour versus Cr concentration, the origin of these centres is discussed in terms of perturbed substitution.