We present our recent achievements in the growth and spectroscopic characterization of KYb(WO4)2 crystals doped with erbium ions ~hereafter KYbW:Er!. We grew single crystals of KYbW:Er at several erbium concentrations with optimal crystalline quality by the top-seeded-solution growth ~TSSG! slow-cooling method. We carried out spectroscopic measurements related to the polarized optical absorption and optical emission at room temperature ~RT! and low temperature ~6 K!. The splitting of the excited energy levels and the ground energy level of erbium in KYbW were determined, derived from the absorption and emission measurements at 6 K, respectively. We determined the near infrared, around 1.5 mm (6667 cm21), emission channels from the emission spectrum, and used the reciprocity method to calculate a maximum emission cross section of 2.7310220 cm2 for the polarization parallel to the Nm principal optical direction for the 1.534 mm (6519 cm21) infrared emission. We measured the lifetime of the 2F5/2→2F7/2 transition of ytterbium and the 4I13/2→4I15/2 transition of erbium at RT for several erbium concentrations. Finally, we present the Judd-Ofelt calculations for the KYbW:Er system.