<p>The structural characteristics, optical properties and growing features of laser LiNbO₃:Er(0.16–3.1 wt%) crystals were studied by IR absorption spectroscopy, X-ray diffraction analysis, photoluminescence, and optical microscopy. It was established that the shape of MeO₆ (Me–Li⁺, Nb⁵⁺, structural vacancy <i>V</i>) octahedra significantly depended on dopant concentration which exceeding the «threshold» value ([Er]≈2.5 wt%). At [Er] = 3.1 wt% the MeO₆ octahedra shape tended toward to regular one, and the composition of the crystal approached the stoichiometric one. It has also been established that the structure of LiNbO₃:Er crystals ([Er] ≥ 2.8 wt%) significantly reduces the number of deep electron traps, such as Nb_Li point defects, which can cause optical damage to LiNbO₃ crystals. It was first discovered that some of the Er³⁺ emission lines were absent from the luminescence spectrum of "post-threshold" LiNbO₃:Er(3.1 wt.%) crystal. It was caused by interaction between Er_Li and Er_okt defects and it led to quenching some Stark components of emission transitions of Er³⁺ ions. According to the results of optical microscopy it was shown that the crystallization mechanisms for the crystals grown at high ([Er] ≥ 2.8 wt%) and lower ([Er] ≤ 2.8 wt%) dopant concentration differed significantly. A connection was determined between the macrodefects of LiNbO₃:Er crystals and subtle features of their structure.</p>