The doped nonlinear optical (NLO) crystal Yb:GdCa4O(BO3)3 (Yb:GdCOB) has been grown by using the Czochralski method, with large sizes and good optical quality. The polarized absorption and fluorescence spectra have been measured and analyzed according to the Judd–Ofelt theory. The ground-state energy-level splitting is 1002 cm−1. The spectral parameters of the crystal such as the emission lifetime, the absorption cross-section, and the peak emission cross-section have been calculated. In comparison with established laser crystals the results suggest that this crystal has potential as an efficient self-frequency-doubling (SFD) laser operation in the green.