Abstract
In the present work, the optical properties of Er and Er/Yb doped stoichiometric and congruent lithium niobate crystals have been investigated. Low temperature (LHeT) absorption spectra show the appearance of at least six non-equivalent optical centres, with similar structure in Er and Er/Yb co-doped congruent and stoichiometric crystals. In Er/Yb co-doped crystals new centres are also detected. Site-selective spectroscopy reveals differences in up-conversion efficiency and lifetimes between the different centres. An efficient energy transfer from Yb3+ to Er3+ is observed after Yb3+ pumping. Using the rate equations formalism it is shown that population inversion of the Er3+ uper laser level is attainable at sufficiently low pumping levels, making this material suitable for laser applications.
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