Combined Excitation Emission Spectroscopy Studies on Erbium Ions in Stoichiometric Lithium Tantalate
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1111-D07-09
Combined Excitation Emission Spectroscopy Studies on Erbium Ions in Stoichiometric Lithium Tantalate N. Woodward, K. Miyahara, A. Toulouse, P. Capek, and V. Dierolf Physics Dept. Lehigh University, Bethlehem, PA 18015,USA ABSTRACT We present our site-selective spectroscopic studies on Er3+ doped nearly stoichiometric lithium tantalate (LiTaO3) and compare the results with earlier studies performed on the same dopant in the isostructural lithium niobate host. We present our results in terms of the number and spectroscopic characteristics of the incorporation sites. Overall, the sites found in LiTaO3 closely resemble in their behavior the ones found in LiNbO3 such that the conclusion about the nature of the site drawn in the latter host can be transferred to LiTaO3 as well. INTRODUCTION Rare earth doping of ferroelectric materials such as lithium niobate (LiNbO3) and the isostructural lithium tantalate (LiTaO3) add to the favorable electro-optical, acousto-optical, and nonlinear properties of the host the ability to add active centers for use in lasers and optical amplifiers. In particular for integrated-optical devices in which waveguides are produced by Tiindiffusion, proton exchange, or by edging of ridge structures, ferroelectric hosts offer a high degree of functionality and great potential. For this reason, extensive studies of the spectroscopic properties of many rare earth ions have been performed for the LiNbO3 host material [1-3]. Much less is known for lithium tantalite (LiTaO3), although it offers better resistance against optical damage making it a more favorable host for high-power lasers in the visible spectral region. We present our site selective spectroscopic studies on Er3+ doped, nearly stoichiometric LiTaO3 samples. While the Er3+ ion is well known for its highly efficient emission in the telecommunication window around 1.5 µm, it offers also emission in the visible at around 550nm and 650nm that can be excited through up-conversion with widely available powerful semiconductor lasers around 980nm. To this end, we focus on the excitation around 980nm and address the following questions: • What are the Er3+ incorporation sites and how do they compare with the ones found in LiNbO3? • How do the different sites participate in the up-conversion processes? • How does the defect distribution change under thermal annealing? EXPERIMENTAL TECHNIQUE We address these questions using combined excitation emission spectroscopy (CEES) in which we record a large number of emission spectra while continuously varying the excitation wavelength. Details of this technique and its potential are described in Ref [3,4]. The nearly stoichiometric LiTaO3 sample was grown by the double crucible technique and was obtained by OXIDE. The dopant level was about 10-2 mol% or about 2*1018at./cm-3. The sample was cut as a z-cut wafer.
Figure 1. Energy level scheme of Er3+ in LiTaO3. The transitions relevant for this work are indicated including the expected polarization properties for C3v point symmetry. In particula
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