Site-selective spectroscopy of Er3+ and Er3+Yb3+ doped stoichiometric and congruent lithium niobate

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