Erbium-doped GaN (Er:GaN) quasi-bulk crystals are emerging as a promising novel gain medium for high energy lasers emitting at the retina-safe wavelength window of 1.5 μm. We report the polarization-resolved photoluminescence (PL) emission spectroscopy studies, which revealed that the pumping efficiency with the excitation polarization parallel to the c-axis of GaN (E → ∥ c →) is significantly higher than that with the excitation polarization perpendicular to the c-axis of GaN (E → ⊥ c →). This phenomenon is a direct consequence of the inherent polar wurtzite GaN lattice, giving rise to a net local field, surrounding each Er ion, along the c-axis of GaN. The temperature dependent behaviors of the PL emission spectra were explained in terms of the Boltzmann population distributions among sublevels within the 4I15/2 ground state and the 4I13/2 first excited state of Er3+ in GaN, thereby providing an improved understanding regarding the origin of the dominant emission lines observed near 1.5 μm. The results suggested that the polarization field in GaN can be exploited to enhance the effective Er excitation cross section by manipulating the polarization of the excitation light source.