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Abstract
This study focuses on the spectroscopic characteristics of novel optical impurity sites oflithium tantalate synthesized via the sol gel process. The intrinsic Li+ decit of the congruentcrystal, due to the thermodynamic phase boundaries of the melt, results in the occupationof these defect sites by the Cr3+ dopant ions. The phase boundaries are avoided with sol gelprocessing. As a result, crystals produced by the sol gel process have a composition closerto stoichiometry. Like the congruently grown crystals, these crystals also show a preferentialsubstitution of the Li+ sites for the dopant Cr3+ ions. The spectroscopic characteristics ofsol gel processed ceramic are similar to the congruently grown crystal. The indication of thesol gel synthesized samples' higher quality crystals are given by their longer radiative decay.The assignment of the majority impurity center in the singly doped congruent and sol gelsamples is the Cr3+ ion residing in a Li+ vacancy, Cr[Li].Codoping lithium tantalate with a secondary ion, Mg2+, is found to change the spec-troscopy center from the Cr[Li]. At a Mg2+ 1% concentration and greater, two novel centersare found. An emission from Cr3+ in the high crystal eld strength environment is observedin the R line region and assigned to Cr3+ occupying the octahedral void, Cr[Void]. Theradiative lifetime of this emission is 1.2 ms. A second main center is observed emitting abroad NIR band centered at 840 nm. The lifetime of this emission is 40.8 s, and is assignedto the low crystal eld center of Cr3+ substituting for Ta5+, Cr[Ta].