Erbium concentration control and optimization in erbium yttrium chloride silicate single crystal nanowires as a high gain material

Increasing erbium concentration while minimizing the reduction of photoluminescence is an important task for achieving erbium-based high-gain materials for integrated photonics applications. Here, we demonstrate a strategy of controlled variation of Erbium density in the growth of erbium yttrium chloride silicate (EYCS) ((Er_xY_1-x)₃(SiO ₄)₂Cl)) single crystal nanowires by systematically varying x between 0 and 1. We show that, as a trade-off between high Er density and suppressed upconversion, Er composition x = 0.3 provides the best compromise with the strongest photoluminescence. This optimized Er-composition corresponds to an Er density of 5×10²¹ cm^-3, five times larger than the optimized Er density demonstrated previously for other thin film materials. We estimate that this optimized EYCS is promising in achieving optical gain exceeding 100 dB/cm.